AQUARIUM LIGHTING, Information including Factors, Types, & Use

By Carl Strohmeyer
Updated 2/10/15

OVERVIEW

When choosing your aquarium lighting, there's much more to consider than just "WATTS PER GALLON".

In fact, the 2-5 Watts Per Gallon is a VERY basic start as this "rule" varies depending upon what is kept, what type of lighting, etc. This is very general rule and quite out-dated due to the variety of available modern lights with varying lumens per watt, different wavelengths, focused lumens, PAR, & especially PUR output, etc.

One cannot simply compare one light to another anymore and use the "WPG" rule, even within the same lighting types as there is often much variance.
As an example, a high PUR LED from using PWM & patented emitter bins only need about 4% to 15% of typical aquarium T8 or T12 lamps.
Even then many LEDs available are not of high useful PAR output (PUR). These often use lower quality emitters & drivers, lesser "current reduction" technology, resulting in poor PUR output and higher wattage requirements.

If you are TRULY interested in the "BEST AQUARIUM LIGHTING", Please read this ENTIRE article to understand ALL parameters necessary for your aquarium light determination.

Products described in this article are primarily used because I and other professionals I trust have many years of experience and research with them.
No one should come away with a feeling of obligation to purchase these products, rather a greater understanding of aquarium lighting and their applications.

As you will read later in this article, a watt is simply a measurement of energy, NOT quality of light output. Even lumen output of the lamp is no longer a good measure of lighting parameter performance due to PAR, PUR, focus, and restrike.

There are other factors affecting lighting for your aquarium.
For example: You cannot compare the output of a 150 watt Metal Halide to a 150 watt outdoor floodlight. Nor an 85 watt standard incandescent to an 85 Watt 6400 K SHO Bulb.
What I am trying to say is often it comes down to comparing apples to oranges.

Other aquarium lighting considerations, besides energy (watts) used are PUR, PAR, Lumens per watt, and even output relative to the size of the light.
For example, a SHO that uses 105 watts but is only 10" and is placed into a reflector will be much more efficient as per wattage and space utilized.
Another example is a T-2 bulb that only takes up a small space of 7 mm diameter. This bulb can be a very productive bulb as per lumens per watt (73 lumens per watt!), PAR and space used.

Water penetration is another consideration. Higher frequency "red" light energy is quickly filtered out in water, and many light energy requiring plants, corals, etc. have adapted to light energies found at certain depths of water they naturally reside in.

This overview is just a brief explanation of aquarium lighting.
Please read further for more in depth discussion.It is important to note that Aquarium Lighting is a complex subject, and this article has both more in depth information as well as some basics.
However this is a subject that, by reading one section, will yield incomplete information. For this reason I recommend reading the whole article (as well as links provided) for a more thorough understanding (it may take more than one reading)
I should also note that while I have years of hands on professional experience (since 1978), this is a fast evolving subject of aquarium keeping requiring my constant research and consulting with many others for their scientific expertise/experience. The result is constant changes/updates to this article.

For cynical readers of this article who claim I have a bias; obviously I do, but then this is based on much research and use.
WHY WOULD I RECOMMEND ANY PRODUCT THAT RESEARCH AND EXPERIENCE SHOWS TO BE INFERIOR TO ANOTHER?
In fact many of the Lighting Products I recommend and admittedly sell were not even available in the earlier drafts of this article, It was my research, consulting, & experience that led me to the products I now recommend!!

As a BRIEF generalization, the five most important criteria in determining the light you need are:
• PUR/Useful Light Energy (Probably the most important factor; this is related to PAR, however many lamps can have reasonable PAR output BUT FAIL CONSIDERABLY in comparison when PUR is considered).
• PAR
• Lumens per watt
• Lumen focus (as well as restrike)
• Wattage used

Finally, it is still worth noting that even our best man made lighting is still far inferior to sunlight. So short of placing our aquarium outdoors, all we can do is attempt to emulate at least the most useful aspects of sunlight energy that we can.

Here are other important factors;

1: KELVIN RATING (such as 10,000K daylight bulb):

What is meant by Kelvin Temperature of Lights is not the classic interpretation of what Kelvin is, however I think is should be considered before I move on to our lighting definition of "Kelvin Temperature".

Here is a brief description of Kelvin:
Kelvin is defined by two points: absolute zero, and the triple point of pure water.
Absolute zero is defined as being precisely 0 K and -273.15 °C. Absolute zero is where all kinetic energy (motion) in the particles comprising matter ceases, and they are at complete rest. At absolute zero there is NO heat energy (the total absence of heat). Water freezes at 273.16 Kelvin, and water boils at 373.1339 or 100C.

The true definition of Kelvin is that it is a unit of measure of temperature on the thermodynamic (absolute) temperature scale.

Kelvins, as applied to color temperature of lights, are derived from the actual temperature of a black body radiator. Which is the concept of color temperature based on the relationship between the temperature and radiation emitted by a theoretical standardized material and termed a "black body radiator". This is where the "classic" definition of Kelvin, and how it relates to light, come together. Hypothetically, at cessation of all molecular motion (the black body state of this hypothetical radiator), the temperature is described as being at absolute zero or 0 Kelvin, which is equal to -273 degrees Celsius.See the picture example below:

An incandescent filament is very dark, and approaches being a black body radiator, so the actual temperature of an incandescent filament is somewhat close to its color temperature in Kelvins.

Incandescent lamps tend to have a color temperature around 3200 K, but this is true only if they are operating with full voltage. When a lamp is dimmed below its full potential, its filament is not as hot, and it produces less light. The reduced temperature of the filament also reduces the color temperature downward. An incandescent light dimmed to 10% is considerably more red in color than one at 100%.

Another consideration of the color temperature as applied to lights; color temperature does not take into consideration the spectral distribution of a visible light source. In cases where a light source, such as a fluorescent lamp, arc-discharge burner, laser, or gas lamp, do not have a spectral distribution similar to that of a black body radiator.

A few notes about Kelvin:

Plant chlorophyll absorbs light at wavelengths of 300 to 700 nm Kelvin rating of about 6400 strikes a good balance here, which is why this is the best Kelvin temperature for freshwater plants (and symbiotic zooxanthellae in corals in shallow, perfect conditions).

The lower the "K", the more yellow, then red the light appears, such as a 4500 K bulb.

The higher the "K", the bluer the light appears, such as a 20,000 K bulb.

Higher Kelvin Color Temperature lights penetrate water more deeply, even more so in saltwater, however there is less of the red "PAR spikes" as well.

The human eye mostly sees light around 5500K.

Candle flame = 1850 – 1900 K

Sunlight (1 hour after dawn) = 3500 K

Typical summer light (sun + sky) = 6500 K

Cool white fluorescent = 4200-5500 K

Different nanometer wavelengths can be used to reach the same Kelvin Temperature; just as 4+5 & 1+8 both equal 9, so can different nanometer wavelengths be used for the same Kelvin Temperature. This is why often comparing one 6500K lamp to another can often be "apples to oranges" as for necessary useful light energy (PUR) needed by plants or corals

What Kelvin rating for Plants & Corals;

Here are some observations made by me and others in the professional aquarium maintenance community, some of these are simple observations, while others were based on more controlled tests. Please understand that these are still generalizations!

The Warm White (3500K) & Cool White (4200-5500K) are typical lighting kelvin ratings used in home lighting and is common of lights sold in hardware stores, etc.
While these sources were used years back for both planted and even reef lighting out of necessity (as there were not many options available), these are poor choices due to little essential PUR energy and many more cool white and especially warm white lights are required to delivery this light energy for photosynthetic life.

Unfortunately many LED manufacturers such as Evergrow, Ocean Revive, even the respected Maxspect, & EcoTech LEDs include these kelvin rated emitters in their lights to achieve Photosynthetic Life PUR via a shotgun approach and/or more human pleasing colors.
If you are looking for the highest output in useful light energy for watt of energy consumed, these kelvin color lights/emitters should be avoided!

The 6500 Kevin lamps have produced the best terrestrial plant growth and generally the better freshwater plant growth (as this Kelvin lamp generally has more of the infrared nm spike needed by "higher" plants, but still has some of the 425-500 nm blue).
This Kelvin Lamp can also work with SPS, LPS placed high in the tank water column (nearest the lights) based on the symbiotic zooxanthellae needs found in these corals.
For more depth penetration, blue actinic can be added, such as AquaBeam Reef/Fiji Blue LEDs to balance out 6500K lamp if used in marine reef tanks.

Please note that saltwater absorbs slightly more light energy than freshwater due to the higher density of the water, so 6500K lights will not penetrate as deeply and are not a good choice for depths over 12 inches.

The 9000-10,000 Kelvin lamps also achieve good growth rates, although slower than the 6500 K bulbs in shallow aquariums. 9000 to 10000K bulbs have produced excellent growth with soft corals and LPS, although slower paced SPS growth.
The 10,000K can be a good choice for achieving PAR for better depth penetration than a 6500K bulb (such as 12-20 inch or even deeper aquarium).

The 14,000K light/lamp, will penetrate even more than the 10,000K light while still providing useful PAR (this would be the highest "Daylight" Kelvin temperature I would recommend and still expect good growth in corals, see PAR section). An excellent daylight color for tanks between 15 and 30 inches in depth.

The 20,000 K light/lamp is more blue yet, and brings out all of the fluorescent pigments in many corals making for a very nice appearance. However the many tests and observations show that when used alone, except in tanks over 24 inches, the growth rate of SPS corals can be slowed or even come to a standstill with 20,000 K lamps.

Here is a quote as per their experience with Kelvin Temperature for a freshwater Planted aquarium:

"I had a 175, 6700K Metal Halide over my 22 gallon cube, and then switched it over to a 14K bulb I had when I used to do saltwater just to see the difference. I didn't like the blue appearance nor how it made the plants look odd. True, my neon tetras glowed more blue as did my beta, but the plants looked weird. I went back to the 6700K last night to make my final decision. Everything looked much better under that light. It is under 6700K that I got explosive growth when I added a good, CO2 reactor.
After I switched back to the 6700K, my plants were pearling away, and they had their true colors and natural look again! If I decide down the road to change to a saltwater fish only with live rock, I can still use the 6700K lights [or shallow reef aquarium]. People need to use the proper spectrum - they shouldn't use what pleases them as so many lights are now sold and presented in forums; they must use what pleases what you are trying to grow/raise be it fish, corals, or plants. You become the shepherd so tend your flock accordingly."
Gary Sanders

Kelvin Summary

The Kelvin rating is another area of comparing apples to apples in lights, not just watts.
Although the above is a simplified explanation of Kelvin as it applies to lights; as such you cannot compare a 6500K T8 light to a 6500 MH light (the MH is going to have much more output as you will read later).

However (using a CFL as an example, this can apply to any light type), a 6400K CFL will have a higher useful energy output than a 3500K CFL of the same wattage, this is why an incandescent filament is very low in Kelvin (dark) as derived from the actual temperature as it is just above a black body radiator.
This does not mean that a certain Kelvin bulb is necessarily "better" as factors such as "lumens per watt", watts of energy used, focused lumens, PAR, and especially PUR MUST be considered as well.

2: THE NANOMETER RANGE (SPECTRUM)

A nanometer scale is used to measure the wave length of light energy from cosmic rays to radio waves.
An actinic bulb will have a Nanometer spike at about 420nm, a UVC bulb about 265nm, and a daylight bulb about multiple spikes from 400 to 700nm.
The difference in the wavelength determines how the wave affects its surroundings. It is this wavelength difference that allows short-wave x-ray to pass through walls, while longer-wave visible light cannot pass though the same material; short-wave ultraviolet and x-ray can destroy DNA in living microorganisms and breakdown organic material while visible light will not. All light energy is measured on a "nanometer" (nm) scale. Nanometer means one-billionth of a meter.

This applies to aquariums when we consider the light spectrum and how it applies to our aquariums individual needs: Red light is the first to be filtered out and can only penetrate a short distance. As light waves penetrate deeper into the water, orange and yellow are lost next. Of all the colors of the spectrum blue light penetrates the deepest. Corals need intense equatorial UVA (actinic) as well as other aspects of PAR.
Most higher plants need a balanced PAR/PUR light range which includes the blue and two red spikes required for photosynthesis (see section about PAR & PUR).
The Nanometer scale and Kelvin temperatures come together when applied to aquarium lighting this way; Natural sunlight on a clear day registers at 5500- 6500 Kelvin degrees. Kelvin temperatures less than 5500K become more red and yellow and the higher the Kelvin temperature the more blue the light is.

Most photosynthetic marine invertebrates should be kept with lamps of a daylight Kelvin temperature from 6400-14,000 K (higher Kelvin with deeper specimen placement, not necessarily tank depth). 20,000K daylight lamps can also be used for deeper tanks (over 22 inches) and/or supplementation with more blue lights (400nm- 490nm).

Photosynthetic invertebrates (many corals, anemones, clams, nudibranch, etc.) also need more blue (400-490nm) than "higher" plants especially as tanks increase in depth, with 465-485 recently being shown the optimum blue. Not only is blue/actinic lighting beneficial to photosynthetic invertebrates, it is also aesthetically pleasing to the eye and the 420 nm blue in particular brings out the colors of many corals/clams.
Osram Oslon now has a "patent pending" LED emitter (the NP Blue) that is the first 'blue' emitter SPECIFICALLY designed for the full PAR spectrum required by marine photosynthetic invertebrates (see LED Section for more)

Freshwater aquarium plants benefit from lighting with a Kelvin temperature in the range of approximately 6500 degrees. Freshwater plants prefer light with more red in the spectrum (see PAR Section).

It is noteworthy that Fluorescent and even more so incandescent lights produce a lot of yellow and green nanometer light, which research indicates is mostly wasted energy in terms of the needs or freshwater plants and SPS Corals. This is where an LED Aquarium Light, Metal Halide, or even (to a lesser degree) T2 Lights excels as there is much less wasted yellow/green light.

See the picture to the left that shows a T8 5500 daylight aquarium light that is commonly sold, this graph clearly shows the wasted green/yellow energy as well as the incorrect spike in orange rather than the correct PAR spike in red 630+ nm

It is also noteworthy that many "terrestrial plant lights" as well as many aquarium plant lights (often of lower in kelvin temperature) have more "red nanometer spikes" than higher kelvin 6500k, 10,000k & higher lamps.
The problem with these lights is that while all plants utilizing photosynthesis require the same essential ABCs of PAR (see the PAR section), the facts of light energy penetrating water requires higher kelvin (6500k +) be added to provide maximum PUR (see Useful light energy/PUR section). Aquatic Plants and corals have adapted/evolved to the natural light energy at certain depth of water and the misguided attempt to adapt these terrestrial plant lights is not going to be 100% effective as a light with more water penetrating blue & slightly lower red nm energy.

3: LUX:

A measure of the intensity of light (referred to the photometry of light), one lux is equal to one lumen per square meter. This is another area of comparing apples to apples in lights, not just watts.
It is noteworthy that a LUX Reading ONLY reports light intensity to which the HUMAN EYE is most sensitive (green light)

While this measurement only includes light visible by humans, this can still be a useful tool for freshwater plants & most corals in marine reef aquariums.
When the Lux is not enough, the zooxanthellae (inside of corals tissues) do not create plentiful oxygen.
The minimum light intensity should be no less than 3,000-lux when it reaches the deepest part of the aquarium. You can over light your coral to a light saturation point (quite hard in my experience, but this should be noted), maximum Lux should be no more than 100,000 to 120,000.
By comparison Lux in tropical reefs has been measured to be between 110,000 and 120,000 Lux at the surface of the reef and 20,000-25,000 Lux one meter below the surface.

4: PAR:

PAR is a good starting point to estimate light energy, but should NOT override the MORE important related Useful Light Energy (aka PUR which literally stands for Photosynthetically Useful Radiation).
I have noticed that PAR is often OVER-RATED by both marine and freshwater plant keeping aquarists, especially many marketing pros and a popular video channel (PUR is MORE important).

PAR is the abbreviation for Photosynthetically Active Radiation which is the spectral range of solar light from 400 to 700 nanometers that is needed by plants & symbiotic zooanthellic algae for photosynthesis (Zooxanthellae are single-celled algae that live in the tissues of animals such as corals, clams, & anemones).
In particular, this is found from actinic UVA to infrared.
UVA to 550 nm contains the absorption bandwidth of chlorophylls a, c˛, and peridinin (the light-harvesting carotenoid, a pigment related to chlorophyll).
Low (near) Infrared is 620-720nm which is the red absorption bandwidth of chlorophylls a and c˛. I should note for the technical "purists" that might read this article, true infrared is beyond 750 nm, but as per my many resources the energy spikes in the red spectrum are generally referred to as near infrared

Photons at shorter wavelengths (UVC) tend to be so energetic that they can be damaging to cells and tissues; fortunately they are mostly filtered out by the ozone layer in the stratosphere. Green light occupies the middle spectrum (550-620nm; what is mostly visible to us) and is partly why chlorophyll is green due to the reflective properties.
Green wavelengths (500 to 525 nanometers) are actually useless for zooanthellic/plant growth. Objects reflect colors that they do not absorb as noted by Oregon State Univ.

Lights that produce light under 500nm will produce a lower PAR reading for a given energy input (wattage), not because less energy is emitted, rather because PAR meters are less accurate below 500nm.Lights that occupy mostly the middle spectrum (500-600/ green-yellow) such as "warm White (2700- 3500K ) will produce LITTLE USEFUL PAR, in other words less PUR (which is discussed in more depth in the next section), unfortunately this FACT is commonly ignored by many, including popular aquarium keeping personalities.However it is the balance of near-infrared and near-UVA that will generally provide your best overall PAR output.

Important Definitions as it applies PAR in plants and zooanthellic algae:
See the graph to the left as it corresponds to each of these definitions.

*A: Phototropic response; having a tendency to move in response to light. Basically this is the Chlorophyll containing plant or algae "moving" to respond to a positive light source to begin the process of photosynthesis (initial growth of plants, zooxanthellae, etc.). This is found in the 410-500nm "blue" spectrum.

*B: Photosynthetic response; the process which begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls.

*C: Chlorophyll synthesis is the chemical reactions and pathways by the plant hormone cytokinin soon after exposure to the correct Nanometers wave length (about 670 NM) of light resulting in the formation of chlorophyll, resulting in continued growth of a plant, algae, zooxanthellae and the ability to "feed" & propagate, and without this aspect PAR (670 NM light energy), zooxanthellae and plants cannot properly "feed" propagate. The results of the lack of this high PAR "spike" would be stunted freshwater plant growth, and eventually poor coral health in reef tanks. This lack of near-red light over 630nm is common to many so-called aquarium lights (such as the diagram at the bottom of the Nanometers section).

* When the amount of energy used (in watts) is considered, this can include 6400 SHO lamps which can generally penetrate most freshwater tanks well and also perform well in marine reef tanks UNDER 18 inches of depth when balanced with blue lights necessary for the higher need of 420-485nm light energy by symbiotic zooanthellic algae).

Further PAR Information;
As the reader here can see, there are three main spikes in the PAR spectrum, with all three being important, and all three are generally incorporated more or less in a daylight bulb of approximately 6500K.
As a light energy penetrates deeper through water, these "red spikes" need to move slightly "left" (lower) on the nanometer graph so as to allow for proper use of PAR (in other words Photosynthetically useful radiation; please see the PUR section).
This means higher kelvin overall lighting color temperatures of 9,000k to as high as 20,000k may need to be employed.This can vary with light type though as not all so-called daylight bulbs are the same, see the Useful Light Energy section of this article.

Besides the obvious depth penetration, it is also noteworthy that most zooanthellic algae need more of the blue spike than "higher plants", hence the popularity of actinic lights for reef aquariums. However the general optimum nanometer range is about 450-485nm.
An advantage of the latest technology LED lights is having a more precise 450-485nm blue as well as some 420-450 nm Fiji/violet lights/emitters for certain deeper reef specimens.
For this reason it is a good idea to have extra actinic for corals/clams that depend upon zooanthellic algae, while at the same time limiting blue/actinic in freshwater aquariums to avoid excessive green algae growth.

As well, a popular trend in LED lighting is to utilize NUV light /emitters that emit light energy between 300-400 nm, HOWEVER as per current known science this light energy is NOT USEFUL for your photosynthetic life and is SIMPLY WASTED LIGHT ENERGY! Part of the reason for this trend is that this makes many corals pop with color since this light range is similar to a black light, but if used, this light energy CANNOT be counted as part of your necessary light energy.As an example, if your Light is 140 watts but has 20 watts as NUV blue, you essentially have a 120 watt light!

Planted Freshwater Aquariums: It is also important to note that freshwater algae also prefer more of the "blue" light so the excessive use of actinic blue lighting should be avoided in planted freshwater aquariums, as well the use of higher Kelvin Daylight (14,000K or especially 20,000K) should also be avoided in all but the deepest tanks since higher Kelvin Daylight lamps produce higher amounts of "blue" light. Otherwise many freshwater plants may not be able to "out compete" against some algae such as hair algae.

More recent studies show that UVB radiation can bleach coral, so the use of blue lighting under 320nm should be avoided!

Measuring PAR
Although Kelvins (as well as LUX conversions using questionable LUX to PAR conversion factors) are ways of getting rough estimates of PAR, only a Specific PAR Meter (also called Quantum Light Meters) can give you the best measurement of this aspect of determining your tanks lighting requirements (both at the surface and under the surface)

Currently accepted numbers measured as µMol•m˛•sec (also referred to as micro mols or mmol) are 50 mmol for most plants or corals such as Nemezophyllia, while Acropora can require higher PAR outputs.
Keep in mind though, that if one light is using a shotgun approach to achieving a high PAR reading with wasted energy in spectrums outside known needed PUR, you may need a higher PAR reading, while the reverse may be true of a very efficient PUR light that might achieve excellent results at 50 mmol compared to the "shotgun" light that might require 200 mmol for the same corals or plants to achieve good results.
It is noteworthy that a study of a Coral Farm in Bali showed no more than 200 PAR from noontime tropical sunlight at the depth the acropora were being grown!
Reference: PUR vs PAR in Aquarium Lighting

HOWEVER, keep in mind that a PAR Meter is NOT accurate in important light energy spikes WITHIN the 400 to 700 nanometer range, so while one light might measure a higher PAR mmol reading, another light might be still superior due to the more important PUR output.This is where I have found the use of a PAR Meter to determine light efficiency VASTLY OVER RATED and why comparing lights based SOLELY on PAR readings is folly!

As an example, just within the same brand of aquarium lights (AquaRay); A 12 Watt Fiji Blue LED fixture has a PAR of 38 at 400mm while the 12 watt Marine White LED has a PAR of 50 at 400mm.
BOTH use the same amount of energy, and in fact the Fiji Blue is actually deeper penetrating, YET the Marine White has a higher PAR reading. This is not to say the Marine White LED is bad, ONLY to show the folly of rating a light based solely on PAR readings!!!!

Some organisms, such as Cyanobacteria, purple bacteria and Heliobacteria, can make use of the unusable light discarded by the plant kingdom, in this case, light outside the PUR range required by plants, which is why Cyanobacteria thrive in lighting conditions that include more yellow light energy.

In the case of Red Slime Cyanobacteria, these Cyanobacteria do not use the PAR spikes at 465nm and 675nm and instead utilize more of the middle yellow and green light spectrum that is most common fluorescent (even so-called aquarium fluorescent lights) and incandescent lighting.

*Fish Health:
Many recent studies have shown the importance of full spectrum lighting (which will generally encompass a high PAR value) as it relates to health in humans & animals, can be extrapolated to fish as well for a disease prevention which is why good lighting should not be restricted to Reef Marine or Planted Freshwater Aquariums, but to fish only salt or freshwater tanks as well.
In fact the medical community is now utilizing 6400K SHO lights (full spectrum lights) due to increasing studies that show better immune function, mental health, and more. Animal studies support similar results as well.

5: Useful Light Energy (PUR):

PUR (Photosynthetically Usable Radiation) also known as "Useful Light Energy" is what concerns us as aquarium keepers even considerably more than PAR in providing correct lighting.
Yet there is a lot of confusion, especially when considering LED Lights as many sellers and aquarium keeping personalities such as "Mr. Saltwater Tank" will hype high PAR values while ignoring PUR.

PUR is that fraction of PAR that is absorbed by plants & zooxanthellae photopigments thereby stimulating photosynthesis. As noted above, PUR are those wavelengths falling between 400-550nm and 620-740nm.
A Spectrograph is an incomplete but still useful method to rate PUR.

The picture above demonstrates how three LED emitters of equal lumen and PAR output can be quite different in PUR and thus more wasted yellow/green energy.

It is noteworthy that whereas higher plants (generally kept in planted freshwater aquariums) require more of the infrared aspect of the PAR Spectrum while the zooxanthellae found inside many sensitive corals require more of the Blue spike 400 -550 (465-485 in particular according to more recent research).
For this reason either/both higher Kelvin Daylight and actinic/blue is required for many reef aquariums while "near-infrared" is less essential and in fact does not penetrate water much anyway.

*As noted in the PAR section the exact nanometer spikes will need to be lower so as to provide the actual PUR, for this reason popular a cool white or "red" 5000-5500k plant light is NOT the best light for any water application except for very shallow water since the spikes are not adjusted for water penetration. Balancing these plant lights such as the "Aqua Flora" with 6500k to 10,000k lights is necessary for best results (such a combination may have the added benefit of certain plants growing more toward the surface).

*It is also noteworthy as per recent head to head studies with Acropora corals that photosynthetic corals found in waters increasing in depth have adapted to PUR of increasingly bluer light spectrums (although not all blue light either) and thus lights with too much red can slow certain coral growth!

The ability of newer technology lights to pin point the exact nanometer spectrums in output results in much less wasted energy and allows for a light of considerably lower wattage to actually out produce another bulb of higher wattage that wastes much of its energy in light bands that are not useful for life processes (this is major reason the "watts per gallon rule" is so useless when applied to modern technology).

Even the best of fluorescent lights that are a Kelvin temperature of 6500K use a percentage of their light energy in the yellow and green light spectrum which is mostly useless for aquarium plants or corals.
One aspect of a higher Kelvin (10,000- 14000K) daylight lamp is more efficient penetration, although Kelvin temperatures much over 14000K loose much of the important 700nm "spike" which deeper water specimens have adapted to.

The picture to the left demonstrates this with two 15 Watt CFL (30 watts total) vs. one 3rd generation 12 Watt Marine White LED (daylight 14,000K).
This picture is taken with a camera that filters out certain wave lengths allowing for a better viewing of the difference which is otherwise not easy to discern, however the picture shows how the LED on the left has less of this wasted yellow and green than the CFL lights on the right.
Otherwise the light output appears the same, although this is still important when you consider that this is achieved with only 12 watts of LED vs 30 watts of Compact Fluorescent lights.

With some LED Lights, new technology LED emitters can be selected for the exact wavelength of light, thus much less useless yellow or green light is emitted, so although the LED may seem less bright than some HO lights with the naked eye (such as T5s or MH) the actual output of light energy in spectrums we cannot see is much higher. This is why gauging a light by what you see is highly inaccurate.

The Picture to above/left shows the light spectrum as seen through a special 3D lens which breaks apart the light spectrum. This provides a dramatic example of how much of the light energy the 4000K CFL is in the useless yellow spectrum (the 4000K is not a terrible bulb either, as many still use this for plants). The TMC Reef White in the picture shows a much more complete light spectrum and much less wasted energy in the useless light spectrums.

IMPORTANT Further/Newer Information as to Useful Light Energy:

As alluded to earlier in this section, EVEN a Spectrograph (which I admittedly use to make certain points) should not be the only determining factor for "Useful Light Energy" as these only rate the light spectrums of a light in air, NOT under water so as to determine PUR.
However when increasing depth of water are thrown into the equation, in particular for photosynthetic marine life, these spectrographs become less accurate as these corals and other photosynthetic marine life have adapted to the wave lengths of light energy that reaches their depths, which the spectrograph cannot show.
Obviously this is more blues and/or "bluer" daylights (such as 14,000k or 20,000k).
For this reason I prefer the less scientific, but in my opinion more accurate term of "Useful Light Energy" over PUR.

Further explanations to hopefully convey the importance of the concept of "Useful Light Energy";

I have noted that a dozen "hardware store" cool white fluorescent lights can provide adequate lighting for a planted aquarium and even basic reefs, however it would only take a few correct kelvin T5 lights to accomplish this same task.
The point is that even a T12 cool white provides some useful light energy, but it takes copious amounts of these lights (& wattage) to work correctly (in other word many more watts of electricity)

In another comparison; one can use one of the many LED panels commonly sold that use 90-120 watts (or more) that all use "Current Reduction" instead of the vastly superior PWM controllers to light a reef or planted aquarium, OR you can use a LED Fixture that utilizes the best technology emitters, PWM Controllers, & drivers available such as only found in a few "higher end" LED Lights which produce more PUR from less emitters & watts.
This is similar to the first example as lower end emitters, controllers, & drivers do NOT pin-point the important light wave lengths (spectrums) that the best patented emitters and Pulse Width Modulation Controllers can do.

One could use nothing but mid range PAR green emitters (which many popular LEDs actually do), versus using an emitter such as the Osram Oslon NP Blue with the same input wattage and actually obtain a higher PAR, YET the Green emitters have basically NO PUR as references already cited here prove!!

As a final comparison, it is important to note as per PUR, that for instance one 6500k light is not the same as another as there is more than one way to mix light "colors" (wave lengths) to achieve a certain kelvin temperature rating.
Think about how mixing all paint colors will produce black, while the mixing of all light energy produces white. We as humans may notice this to some degree, however we do not have the ability to pick out particular colors such as a honey bee can.
As well photosynthetic aquatic life also has differing abilities to pick out the useful light energy it needs for life processes and even though the kelvin temperature or PAR readings may be equal, the light energy that provides this kelvin "color" is NOT.

Below is a picture of a Reef Aquarium (88”x32”x24”) that includes Acropora corals lighted with ONLY VERY high PUR but lower wattage AquaRay NP 1500 & 2000 LED lights (this tank has been running with these lights for 6 months at the time of the picture).

6: LUMENS:

The international unit of luminous flux or quantity of light used as a measure of the total amount of visible light emitted. The higher the lumens, the "brighter" or more "intense" the light looks to the human eye. You can figure lumens per watt by dividing the lumens your lamp lists by the wattage the fixture lists.

Knowing your lumens per watt is just one more small piece of the "aquarium lighting puzzle".
For example a T12 light that is rated at 20 watts with a total lumen output of 800 lumens has a lumen per watt output of 40. While a 13 watt T2 bulb rated at 950 lumens has a lumen output of 73 lumens per watt. This is a clear example that the watts per gallon rule is severely flawed, as the 13 watt T2 (or two of these) is clearly the better choice for a 15 gallon planted aquarium and this does not even take into consideration the PAR/PUR which is also important for plants/corals.

Focused Lumens;
It is also noteworthy that even the lumen output can be deceiving when considering aquarium lights.
The best LED Lights are a good example of this as these newer technology lights have extremely focused light energy with little essential light energy lost (such as by Restrike), unlike almost every other type of aquarium light currently available.
With this focused energy a "high end" LED often requires half the lumens (or often even less) to provide essential light energy to plants, corals, etc. The newer generation LED lights have considerable less loss of lumens at 20 inches than a CFL light (as per tests that show 166% more lumens for the same wattage LED as compared to a common CFL of equal wattage). As another example, think lasers, although not nearly as focused as a laser, the best modern LED emitters are much more focused than other types of commonly used aquarium lights thus requiring less input energy for the same results.

Caution as to using Lumens as a useful measurement of Light Output:
While lumens are a important useful measurement for standard household light bulb comparison, it is only a part of the equation for aquarium use, especially when this measurement is applied to new technology lights employed by aquarium keepers (such as LEDs).
As an example of just one aspect where the lumen measurement falls short is when Kelvin is considered; a cool white lamp emitting 1000 lumens at a color temperature of 5,500K will not emit as much PUR as a lamp emitting 1000 lumens at 6,500K.
More over, when compared to "Useful Light Energy" (PUR), Lumen output falls well short as useful comparison of light output.
This said, I am not saying Lumen output and focused lumens are useless, as these parameters are a piece of the light parameter "pie", but often it is overrated and these parameters should only be taken as a part and a small part at that when compared to PAR and especially PUR.

7: WATTS:

Watts equal one joule of energy per second. For us, it's a measurement of how much energy our light fixture is using NOT of light output!
This is why the old rule: "3-5 watts per gallon" can be deceiving, and this rule is only a starting point at best. This archaic rule was more accurate when all that was used were T12 lamps which is what this rule is based on.

Keeping this in mind the average T12 has a lumens per watt rating of 40, which means you would need half as many watts of a bulb that produces 80 lumens per watt (assuming PUR & other aspects are equal). Another example is the lumens per watt of the CFL when compared to standard incandescent lights.

The term "watts per gallon" is getting more archaic with the newer T-2, T-5, CFL, the SHO, and especially the new reef compatible LED lights.
Even within LED Lights, one 30 watt LED is not equal to another 30 watt LED.
An example, you cannot compare a 30 Watt TMC Ocean Blue to a 130 watt EcoTech Radion. However if you were to use an equal wattage of the TMC Ocean Blue or Reef White, you would have more actual useful light energy (PUR) with these per watt of energy used than the EcoTech (this is not to say the EcoTech Radion isn't reef capable LED).Please read the FULL article to understand why I made this statement such as the fact the EcoTech uses COOL WHITE emitters & "current reduction" technology.

Keeping this in mind; 'watts', when applied to a standard fluorescent tube are spread over longer bulbs as the wattage increases. For instance a standard 30 watt T 8 bulb is 36" while a standard 20 watt T-8 bulb is 24".
Many high output light such as the Metal Halide or the more economical SHO PC bulbs use a lot of 'watts' in a small amount of space. The 110 watt SHO bulb uses 110 watts in 10" or even less if mounted in a pendant.

If PAR (& more importantly PUR) is considered to correspond more or less to the visible region, then a 400 watt metal halide lamp provides about 140 watts of PAR. A 400 watt HPS lamps has less PAR, typically 120 to 128 watts, but because the light is yellow it is rated at higher lumens (for the human eye).
Wattage of lights versus PUR is where the actual watts used when comparing one light to another is simply not at all accurate, such as comparing a MH or LED of say 75 watts to T12 cool white Fluorescents also of 75 watts; these cool white T12s will simply not even be close to "useful light energy" output at 75 watts as the LEDs or MH (of coarse other factors apply to the MH and LED as not all are equal here as well).

The bottom line is 'watts per gallon' can be used when comparisons are "apples to apples" such as one Patented High output LED emitter of the same brand to another, but not when comparing a T8, to a T5 to a T2 , to a Metal Halide and especially to an LED.
An example of an "apples to apples" comparison would be the Patented emitters used by TMC require .8 watt per gallon (or less) under 24 inches of water for high light requiring reef life (.6 watt per gallon or less for planted freshwater aquariums).

8: CRI:

To help indicate how colors will appear under different light sources, a system was devised some years ago that mathematically compares how a light source shifts the location of eight specified pastel colors on a version of the C.I.E. color space as compared to the same colors lighted by a reference source of the same Color Temperature. If there is no change in appearance, the source in question is given a CRI of 100 by definition. From 2000K to 5000K, the reference source is the Black Body Radiator and above 5000K, it is an agreed upon form of daylight.

A CRI of 100 has a heavy red spectrum. The color temperature is 2700 K for incandescent light and 3000 K for halogen light. An incandescent lamp, virtually by definition, has a Color Rendering Index (CRI) close to 100.
This does not mean that an incandescent lamp is a perfect color rendering light source. It is not. It is very weak in blue, as anyone who has tried to sort out navy blues, royal blues and black under low levels of incandescent lighting. On the other hand, outdoor north sky daylight at 7500K is weak in red, so it isn't a "perfect" color rendering source either. Yet, it also has a CRI of 100 by definition.

CRI is useful in specifying color if it is used within its limitations. Originally, CRI was developed to compare continuous spectrum sources whose CRI's were above 90 because below 90 it is possible to have two sources with the same CRI, but which render color very differently. At the same time, the colors lighted by sources whose CRI's differ by 5 points or more may look the same. Colors viewed under sources with line spectra such as mercury, GE Multi-Vapor® metal halide or Lucalox® high pressure sodium lamps, may actually look better than their CRI would indicate. However, some exotic fluorescent lamp colors may have very high CRI's, while substantially distorting some particular object color.

Technically, CRI's can only be compared for sources that have the same Color Temperatures. However, as a general rule "The Higher The Better"; light sources with high (80-100) CRI's tend to make people and things look better than light sources with lower CRI's.
Why use CRI if it has so many drawbacks? It's the only internationally agreed upon color rendering system that provides some guidance. It will be used until the scientific community can develop a better system to describe what we really see. It is an indicator of the relative color rendering ability of a source and should only be used as such.
Source: Color Rendering

To be blunt, CRI is NOT a parameter that is important in determining the best aquarium light, but it is included here since many mistakenly tend to consider it an important parameter, in fact most lights sold with CRI ratings prominently displayed are intended for home or industrial use, NOT aquariums! However many low end aquarium lights such as the Fluval LED Lights still refer to CRI since their PAR and more importantly PUR IS POOR when compared to the true top notch lights now available.

AQUARIUM BULB TYPE:

*T-12;

A standard pin, 1-1/2" wide bulb. The main caution to the use of these bulbs for aquariums, is the use of shop lights as an inexpensive alternative to many aquarium lights. A 4100 K cool white shop light is not going to come close to a 6400 K daylight lamp that is of peak PAR efficiency (even if you match lumens).
This bulb will generally use more watts and have a lower lumens per watt ratio (usually around 40) and is common in shop lights and even some aquarium bulbs. These are generally the least expensive lamps to purchase and even though they may be "old school", some still try to make up for the low technology with the fact you can purchase several for a low price to make up for poor efficiency.

*T-8;

A standard pin, 1" wide bulb. As compared to the T-12, a 48" T-12 will use 40 watts, while a 48" T-8 will often use 32 watts (although not always), making the T-8 a more efficient lamp than the T-12.
The T-8 is the more common bulb/lamp size in many basic aquarium lights.

*T-5;

Generally around 13 mm in diameter. This is a mini pin bulb which generally uses even less watts per lumen than many than T-8 bulbs. A common lumens per watt output for T-5 lamps is around 65.
The T5 became very popular in the early 2000s among both plant keeping freshwater aquarists and reef keepers for good reasons; they are compact, come in MANY varieties and high lumen per watt outputs (as a broad generalization only requiring 2 to 4 watts per gallon for more shallow planted/reef applications depending upon tank depth and other factors). While the T2 is the latest in straight tube fluorescent lights, the T5 still is better suited for aquariums over 20 inches in depth, if only because the T5 is available in much higher wattage per lamp and more varieties.

• One negative with T5s is that the quality control on these lighting fixtures (not the bulbs themselves) is often lacking. This problem tends to be with some of the HO T5 light ballasts/fixtures, and in fact tends to be a problem with VHO Compact Light Fixtures as well. For this reason my recommendation is to avoid the VHO or HO T5 or Power Compact CFLs and stick with the standard output versions.
If higher output is needed consider the newer technology SHO, LED or MH lights instead, in fact when cost per lumen as per lifespan is considered, a LED Aquarium Light Fixtureis now a much better deal (since LEDs can last 50,000 hours vs. the common 8000 lifespan of a HO T5 or VHO Power Compact).

Another consideration for higher output requirements, such as large planted freshwater aquariums, consider the vastly superior in terms of performance and cost SHO light over the T5.

As a final point, the T5 is a good light, but it is often pushed by aquarium keepers that are not aware that technology has passed them by since the T2, SHO, & LED are newer generation lights. For this reason I personally no longer sell nor recommend T5s for those looking for new lights for their aquarium (both fresh & saltwater), as the you can generally find better results depending upon application among the T2, SHO, & high end LEDs (not the cheapie LEDs flooding the market though))

*T-2;

These bulbs are the latest fluorescent technology yet.
They measure only 7 mm and allow for several bulbs in a small space. A 13 watt 20 inch T-2 Bulb (6400 K) produces 950 lumens which is 73 lumens per watt in a very small space with low wasted green/yellow light energy that is often found in other Power Compact Lights!

As little as 1 watts per gallon (low light) to 1.75 watts per gallon (high light) for a planted aquarium is all that is needed from these T2 Lights! (depending upon tank depth, and not for tanks over 18 inches max; consider SHO for tanks over 18 inches).

Quite bluntly, these T2 lamps and fixtures are about the best fluorescent lamps in a small space I have seen! These are very useful for small to medium planted aquariums or Nano Reefs or even shelves for betta breeders (although ONLY as a compliment in larger aquariums over 20 inches in DEPTH for freshwater and 16 inches for marine). The picture to the left displays the remarkable amount of light these fixtures put out for little energy usage. These aquariums are well lit by ONE SINGLE 13 Watt T2 light fixture!

The linkable fixture feature is also a nice aspect of these T2 lights/fixtures (this allows for use in larger aquaria such as 60 gallons).
Some T2s can be linked with small extensions which are available with these T2 fixtures. These allow you the choice of either placing a T2 in series (end to end) or in parallel (which is useful if you desire a higher output yet in a small space or to utilize a daylight and blue/actinic light parallel to each other) with out having to add multiple outlets/plugs.Product Reference: T2 Lights, Fixtures

The newest generation T2 Lights require less watts to provide the same useful light energy (in particular required by plants & coral) than all other lights except for LED.
Speaking of LED Lights, the T2 makes an excellent compliment to LED Lights (for cost savings as well).
The picture to the left displays a newly set up planted freshwater tank that has 4 2nd generation TMC GroBeam 500 LED and 4 6400K T2s as well as a Mylar Reflector.

Please Click the picture to enlarge

When all important parameters are considered (PAR, useful energy, lumens per watt, etc.) the a typical 6400K T2 about 40% of the wattage of a standard T8/T12 aquarium light for the same useful output (a 13 watt T2 will equal 30 watts of most older fluorescent aquarium lights).
The T2 will even exceed a comparable T5 light by about 20% in useful light energy output in up to 20 inches of water.

T-2 lamps especially good choices for smaller planted FW and Nano reef due to their extremely high efficiency and output. (only LED lights are more efficient).

Please click on the picture to the left for a comparison between 2 CFL 15 Watt lights and just one 13 Watt T2).

In fact these lamps are even a good choice for many aquariums such as 60 gallons and larger since each fixture can be linked together forming a larger fixture.
For instance I have used two T2s linked together for some 60 gallon FW aquarium and two sets of two (placed in parallel in the hood) for planted 60 gallon FW aquariums.
T2 Fixtures/lights also work well in Marine Aquariums (particularly pico/nano reef & Refugiums) since these lamps in the 6400 K version have a high output in PAR required for symbiotic algae that live within corals. As well actinic/blue versions of the T2 light are now available to the consumer.

The Aquarium above is a planted 10 gallon with two 11 Watt T2 fixtures

One negative with the first generation T2 as compared to the older T5 is that there are not the selection/variety, however as noted in the previous paragraph, blue/actinic T2 lights are now available to the hobby.
As well, there is not as much need for some of the versatility other lights have, as the T2 has its own versatility such as small space combined with higher lumen per watt output.

I would also counter uninformed aquatic forum comments such as this one: "T2 are still pretty much a niche market that could be easily overwhelmed by the T5 and they could disappear at any time or just become even more expensive".
The answer is both yes and no. The T5 at one time was still a niche market as well, and more importantly the T2 has grown considerably popularity in Asia (possible due to space concerns) and even in small scale Hydroponics/home green house applications in North America.

One other negative with first generation T2s that goes for T5s (especially the expensive HO version of T5) is that the quality control on these lighting fixtures (not the bulbs themselves) was often lacking. From my investigation of looking at defective items, it seems to be difficulties in good solder in the confined spaces of these small micro lighting fixtures.
This problem seems to be a first generation problem of T2, as the newer generation T2s we are now using do not have this problem based on considerable use.

*VHO Power Compact

This stands for "Very High Output". These come in T-5 thru T-12 standard fluorescent tubes and in the newer power compact (usually 4 pin T6) lamps such as the Current USA, Coralife Quad & Via Aqua Helios VHO.

The Helios & other VHO Power Compact Fixtures come in a variety of sizes with outputs up to 180 watts out of lamps under 40 inches in length, which rival many T5. These higher output VHO fixtures/lamps have higher Kelvin and wattage output than previous generation VHO lamps/fixtures of similar size.

Coralife has a quad lamp VHO (such as the 20 inch; 96 watt fixture) that have high output in small space.

However both these before mentioned lighting systems are a bit pricey in my opinion for the "light output" for the price paid. As well the electronic ballasts contained in not just these, but ALL these VHO styles of CFL light fixtures (Current USA, JBJ, etc.) tend to have a short life span of under 3-5 years in my experience. When the ballasts go out, generally the replacement cost is the same as a new fixture.

With this in mind, I would recommend the SHO Lights which only require an inexpensive incandescent fixture and are vastly less expensive the similar high output PAR light.
I should also note that as of my latest update of this section (VHO), I have found their durability in relation to cost, and output in essential lighting parameters is not as good as T2, SHO or especially LED Lights, which the LED in my tests, feedback, research and experience are the future of aquarium lighting, especially as it pertains to freshwater plant and reef aquariums.

More bluntly, I would generally advice aquarium keepers to avoid the often over hyped VHO Power Compacts or HO T5 in lieu of the SHO, LED, or Metal Halide for high end lighting needs or stick with T2 Aquarium Lights for cost effective aquatic lighting needs.

*PC (or CFL);

This stands for "Power Compact" or "Compact Fluorescent Lamp (light)". These bulbs come in straight pin arrangements, square pin arrangements, and the self ballasted standard incandescent fixture "screw in" type. These bulbs are similar to T-5s and have about the same lumen per watt output (generally around 60 lumens per watt).

The standard medium base version of these lamps will fit in a common incandescent light fixture, making these lights about the most economical lights you can purchase with this kind of output. These are an excellent choice for use in planted Freshwater or even Marine.
See: Compact Fluorescent light bulbs, standard screw in base

These can be used in a basic Nano Reef tank under 30 gallons, especially when the hood already contains incandescent fixtures, as you need not purchase special fixtures for these.

See the picture to the left as an example, please click to enlarge

These self ballasted high PAR lamps are inexpensive and make it easy for even an aquarist on a budget (even a freshwater fish only tank) to provide the best possible lighting within a budget for fish, plant, and even basic Nano reef health!

*SHO Power Compact Lights:

A newer Power Compact that in my opinion is awesome for planted aquariums (in fact the best other than some high end LEDs for planted freshwater aquariums). As well the SHO can be used for reef aquariums (as an addition to LED or Metal Halide)
The SHO Light is currently sold in a self ballasted PC bulbs/light. The 105 Watt SHO Daylight bulb puts out 6300 lumens and is comparable to a 525 watt Standard bulb (click on the picture for a link). This comes out to 60 lumens per watt; however this is a deceptive guide, as you can fit many more of these bulbs in a given space and also utilize more efficient reflectors.

The SHO is already VERY popular with Green Houses/hydroponics and is growing in aquarium use popularity, although it is still relatively unknown to many in the aquarium hobby, although many planted FW and some reef keepers (for Refugium use in particular) are well aware of these lights.
In fact the 105 Watt SHOs were in short supply during each Winter is due to companies purchasing 1000 of these for lighting greenhouses & hospitals.

My point is; if a company (greenhouse business) that needs the correct lighting that are price effective to grow plants for a business, all the more reason these should be used in many freshwater plant aquarium applications.

Keep in mind that there is vastly more research $$$ into horticulture than into aquarium keeping (the money generated by the aquarium industry is just a needle in the haystack compared to most other industries), sadly this point is missed while many continue to use older less efficient, yet often more expensive lighting technology for their planted aquariums.

In fact the medical community is now utilizing these SHO bulbs (& similar full spectrum lights, which is also often making the SHO in short supply) due to increasing studies that show better immune function, mental health, and more. Similar animal studies show like results. I learned of this when inquiring as to why the SHO lights were currently unavailable from the North American distributor, and they pointed out that several hospitals and convalescent homes had purchased over 1500 of these lights. They pointed out the simplicity of these Super High Output bulbs are quickly making these a favorite of the medical community for their full spectrum light needs (I now use a few 65 Watt 6400K SHOs in my home after learning this and there is certainly a difference).

While there are few drawbacks to the SHO light for aquarium use; one such drawback is that in any "tube light" some of the light that shines up from each tube just reflects right back into the tube and is lost (this is called "Restrike"). HOWEVER, the spiral design & especially the use of a reflector tends to limit this minor problem and based on extreme plant growth achieved this is obviously not as much a factor as some may claim (this is essentially a problem with ALL compact Fluorescent lights).
As well, while the SHO does not produce nearly as much heat as a Metal Halide, the simple fact of the wattage used by these lights still produces heat, so a well vented hood or the use of a reflector is advised (any light should be placed in a ventilated hood/canopy as trapped moisture can quickly damage any light whether an SHO, T5 or LED).
Finally the only other potential negative is that these SHO lights are more of a DIY lighting application, not an out of the box and place on your aquarium light applications; so those who do not have DIY abilities, time, or simply desire an out of the box light might find this is not the light for them.

Back to the positives of Super High Output lights; quite bluntly there are few equals for super high output aquarium lighting.
This is especially true for planted freshwater aquariums when cost is considered since these lamps do not require expensive ballasts like a MH (SHO are self ballasted) and generally cost $30 and up per lamp.
See also: Aquarium Plant Care, Information

Since the 6400K SHO requires as little as 2 to 2.5 watts per gallon for the most light demanding plants; Four 85 watt SHOs (or 105 watt for even higher output) can easily handle a 6 foot FW 125 gallon planted aquarium (some T2 or T5 can fill in some more dim spots if necessary)
While in Marine Reef Aquariums this same combination (maybe using 105 watt SHOs) along with one or two high output LED Lights (such as TMC Reef Blue) would work in most reef applications for $500 to $800 for a large aquarium (less for smaller aquariums, or in combination with LED). Consider the 65 Watt SHO for smaller tanks of depths under 15 inches.

The SHO can be mounted into your hood using a standard incandescent fixture. I recommend using an aluminum foil or better an easily made mylar reflector to amplify light downward (& reflect heat away from the canopy). I also recommend venting the hood to remove heat and moisture (a small outward direction fan can be helpful too)

The SHO light is most effective hung as a pendant light using reflector similar to how Metal Halides are commonly installed over an open aquarium. These SHO lamps are also an excellent compliment to MH, VHO or other "strip" lamps for use in reef tanks (in part due to their high intensity in small space and PAR output which is important for the symbiotic coral/algae relationship). Research (albeit older research now) has shown that many stony corals, clams, and other sessile species that depend on photosynthesis of zooanthellic algae not only thrive but also propagate when maintained under Power Compact lighting alone, and the SHO power compact has a MUCH higher useful light output over standard CFL.

The picture to the left shows one way of DIY mounting of a SHO light with a reflector by designing your own "rail" system that fits on the aquarium top. Multiple SHO Lights can be added with just such a mounting system
This tank shows just one of many simple ways to install a SHO light which also includes hanging pendent style, or inside of a canopy, but this picture shows my favorite method.

Please click the picture to enlarge

As of the most recent update of this section of the article, the SHO is easily one of the lights of the immediate future for aquarium lighting (the others are the premium versions of the LED aquatic light, the T2 and some of the newer T5 lights), in particular for planted freshwater aquariums or some reef aquariums.
This is not to say that MH or VHO are bad, it is just when you consider all the aspects of aquarium lighting parameters (not just the out of date watts per gallon rule), then throw in costs of purchase, reliability (a problem with many VHO & some T5 lights) lower heat output (the main issue with MH); there is simply little comparison at this time.

In summary as to SHO lights for aquarium use, what I find amusing is that the only negative comment I have had from someone who actually used an SHO in his 30 Hexagon is that his plants grew TOO FAST with constant pearling and he could not keep up with them due to his work schedule. Honestly this negative is positive proof of these lamps abilities!

In fact, even with quickly improving LEDs (see later in this article), the SHO may still be your best choice when price is considered (it is still often the most popular choice for Hydroponics or Planted Aquariums).

*Metal Halide (MH);

Metal Halide was generally considered the "Kings" of reef aquarium lighting due to depth penetration, output, spectrum, and over all beauty and amount of coral life they help support making most corals "pop" with life (however the newest HO LEDs are now over taking the MH in many aspects of aquarium lighting).
Aesthetically speaking the Metal Halide is also hard to beat, however the latest technology LED lights are now beginning to surpass MH for Reefs and LEDs have been proven to surpass MH with plant growth in nursery/hydroponics environments (one study/test shows a 12 Watt Full spectrum LED producing better growth than a 175 Watt MH of the same type!).

That said for tanks over 30 inches in specimen placement, the Metal Halide is still generally the best available light, especially when used in light combinations that include 20,000K, with other popular Metal Halide Kelvin Color Temperatures being 10,000K, and 14,000K.
The popular "Radium" 150 Watt 20000K Metal Halide Bulb is still a difficult source of reef lighting to beat by any light, especially for many Acropora corals.

As for other light comparisons to the MH, even the newer T-5 lamps cannot achieve the depth penetration and overall output of these lights. Metal Halides generally have very good lumens per watt ratio (although I have seen a lot of variation and even incorrect ratings here); however it is safe to say that MH are generally found with lumens to watt ratios of 50 to as high as 90 which is among the highest of any aquarium lights available.

Metal Halide work via a gas mixture of halides and other elements, the actual light production comes from the small bubble of gas that is held in place by metal wires and/or supports. The electricity running between them and the small gas bubble, heats them, similar to an incandescent filament. This is one of the reasons that Metal Halide bulbs give off more heat than other bulbs.

MH Lights are generally sold in two basic types for aquarium use: the Mogul base & the HQI Double Ended Metal Halide bulbs.
Mogul base screw in Metal Halide bulbs for Aquarium use come in a variety of color spectrum from 10K to 20K (the bluest) and wattages from 250W - 1000W.
German made (Ushio) metal halides have an excellent reputation for producing the best lighting effects for reef aquariums.

The newer Halogen Quartz Iodide (HQI) lighting systems are used mostly on saltwater reef aquariums. HQI bulbs are commonly offered with spectrums of 10,000K and 20,000K. These high-intensity bulbs help corals thrive, but give off less heat than regular metal halide bulbs. HQI Double Ended Metal Halide bulbs have been used in Europe for many years have gained popularity in the U.S. among aquarium hobbyists in the last several years.
Double Ended MH HQI bulbs offer many of the same features as standard mogul base Metal Halide bulbs but are designed differently. These bulbs are much smaller than mogul base screw in Metal Halides and are double ended.
The benefits of using HQI Metal Halide bulbs are that they offer a more clean color spectrum (useful light energy/responsive wavelength), are more efficient, produce slightly less heat, and last longer than standard Mogul Base metal halide lamps.

The downside is the heat that MH lights produce, often resulting in the need for hood fans and even chillers, although the newer open design units such as the EcoSystems USHIO double end fixture and HQI bulb works well for 10-25 or even larger aquariums when other lights are included in the "mix" without a chiller.

*LED (light-emitting diode):

Pictured above, Reef Aquarium including Acropora Coral at the National Oceanography Centre in London using AquaRay LED Lighting (Click to enlarge)

Quickly becoming the new king of reef and planted aquarium lighting with many high end LED manufacturers such as TMC AquaRay, EcoTech, Aqua Illuminations (among others) leading the way.

These LED lights have the same shimmer effect and "popping" of coral life otherwise found in Metal Halide.

This aquarium light type uses semiconductor technology as its light source.
What is noteworthy is that these are "light emitting diodes" NOT bulbs! What difference does this make?
The answer is a lot, as with any electronic circuit these must have an exact voltage to run correctly.

The difficulty in the past (and where many still misunderstand the complexities of LED) is correct wave length of the emitters, which in part are affected by the drivers/circuitry maintaining correct voltage over all emitters.

The high quality LED lights do not have the heat problems, often last 50,000 hours, can produce less useless yellow/green spectrum light (in high-end aquarium LED adjusted configurations), and are very compact.
In fact this lack of much of the yellow/green light (as a percentage) often makes a "high-end" LED look less bright to the human eye, when in fact the opposite is true as per useful light energy (PUR).

The new reef compatible & freshwater planted tank LED's are likely to take over the market along with the T2, T5, & SHO lights as the top manufacturers of LED fixtures become more readily available as the price comes down, while at the same time PUR (useful light energy, their main advantage) & general aquarium compatibility come up.

Since LEDs emit light only in a very specific direction, the installer has the option to illuminate a precise area by simply rotating the polycarbonate tube casing.
For this reason the LED does not need to produce as many lumens of light as most conventional lights. In conventional lights, many lumens of important light energy are lost due to lack of focus, including all power compacts and fluorescent lights in general, but need higher lumen outputs to achieve the same lighting parameters.

Achieving the correct wavelengths in the correct amount has been the challenge and why a simple LED flashlight has about as much in common to an advanced aquarium LED as a paper glider to an 747 jet airplane. This however is also the advantage as much of the useless green and yellow light spectrums can be omitted with correct emitter bins and proper drivers/circuitry.

An example of a new emitter developed just for photosynthetically sensitive reef inhabitants is the 'Osram Olson NP Blue'. This patent pending emitter primarily targets the FULL spectrum of blue necessary for phototropic response, as well it also contains light energy in the full spectrum of PAR, unlike other blue emitters that have come before it. This emitter provides optimum PUR while limiting undesirable algae growth as per use of these emitters.

In my opinion this is one of the most profound recent developments for aquarium LED lighting of late, as ALL other emitters used are either exact bins used for multiple applications or in the case of many patented Cree emitters are emitter bins that are tweaked for aquarium use.
While this Osram Olson NP Blue is a SPECIFIC emitter designed for the PUR requirements of many if not most light sensitive reef inhabitants.
It is currently used in the TMC Ocean Blue NP 1500, with this emitter now in the more focused TMC Reef White 2000 Fixture

It is noteworthy that optimum emitter PUR technology has been a barrier in the past and continues to be the problem with the plethora of LED fixtures made in the same Chinese factories using the same lower "hardware store LED technology" under multiple brand names and sold at many aquarium stores and online big box sellers.

One problem with many low end LED fixtures is even if the emitters used are of reasonably efficient bins, these LED fixtures "daisy-chain" their LED emitters together rather than provide the expensive drivers/circuity needed to maintain exacting voltage to each emitter.This driver/circuitry is essential in maintaining spectral quality over all emitters without which the important PUR will not be optimal.

As well "pulse width modulation" (PWM) is best used for controlling the output of these emitters so there is no change to the spectral output as opposed to using "current reduction" used by many (most) brands of LED fixtures of which the result again is less than optimal PUR and wasted energy as heat instead of light energy.
The over all result is lesser quality light energy from these LED lights that employ dozens of emitters, poor drivers, and current reduction controllers.

As previously noted, this also results in more heat output and the requirement of fans by these "lower PUR" LEDs. This excess heat being driven away by fans simply equals input energy that is NOT GOING TO LIGHTING YOUR AQUARIUM!
In other words it requires a higher wattage "Current reduction" LED fixture to have the same light output of one utilizing PWM.
The bottom line is, if your Aquarium LED uses cooling fans, even if it an expensive LED, it good bet your LED fixture is either using the vastly inferior "Current Reduction" technology or is simply at the very least wasting energy as heat instead of light energy.
As well, electrical usage with "current reduction" is higher and considerably higher when lights are dimmed such as at night which adds considerably to operating costs of any light not utilizing PWM (which is most)

What is important to consider is that unlike fluorescent, incandescent, and other lighting types; very specific emitters require circuitry/drivers similar to your computer.

Simply put, the more emitters along with more specific light output requirements, the more complex and expensive the circuitry and thus NO LED fixture is going to have specific output light energy with say 100+ emitters AND be even remotely close in price to one using 10 emitters if both are using correct LED driver circuitry.
The TaoTronics is a good example of an LED to avoid for this reason if one seeks the highest output of PUR per watt of energy used, not that these do not work, they just need much more energy for the same results as a high end LED using the best emitters, drivers, & PWM (as well the warranties of ALL LEDs utilizing lower tech drivers and "Current reduction" is considerably shorter).

It is also in the area of emitter development where-by development costs are incurred and where many who do not understand the business aspects of these costs, will then question why one LED manufacturer has or can have exclusive patent rights or similar.
Basically ANY 'high end' developer is going to want to recover development costs as quickly as possible and "off the shelf" sales are NOT the way to do this.
The facts are, TMC, CRee, Bridgelux, Osram Olsam, etc. are no different than any other manufacturers in other businesses.
Think about your prescription medications and why a newer "in patent" medications cost so much more than an out of patent generic, this does not mean these generic out of patent medications or emitters are bad, just not the latest and best!

Controlled Tests with Plants and The Aquatic Life Implications;

In tests for plant nurseries (Green House, Hydroponics) full spectrum LEDs such as the newer generation TMC GroBeam Aquarium Lights, 3-10w LED Grow Lights, or even the older generation LED Grow Lights have been proven to surpass even Metal Halide Lights in both growth and useful output.

The picture to the left is the plant growth results comparing the same Kelvin output LED and Metal Halide Lights as measured by a PAR Meter (please click to enlarge view).

The picture to the left shows the useful PAR light energy of a MH compared to a LED Light (both full spectrum daylight).
Please note that this is an older generation "Full Spectrum Daylight" LED used in this controlled test, not the newest generation GroBeam or higher Kelvin Marine White 14000K.

Implications of these tests:

This controlled test has aquatic implications, as photosynthesis is the same whether it be a terrestrial plant, a freshwater aquatic plant, or symbiotic zooanthellic algae found in corals.
The main difference would be that light energy is quickly absorbed by water, especially red light waves and many modern high-end LED fixtures such as an EcoTech Radion, AI Sol Vega Blue, ZetLight ZT 6600, TMC Fiji Blue, TMC Ocean Blue NP, and TMC Reef White 2000 produce the light energy for deeper aquarium water penetration more comparable to the popular 20k "Radium" Metal Halides.

It is still easy to make assumptions from the raw data based on this study with plants that a 12 Watt High Output LED should easily replace one 175 Watt Metal Halide MH of similar rating for marine applications.

Please click on the pictures above for a better view. The first to the left is of a 40 gallon freshwater aquarium with just ONE "GroBeam 600 12 Watt LED" as an example of what just 12 watts of high end emitter LED light can do!
The second to the right is of a 75 gallon with TWO GroBeam 1000 LEDs which is essentially over kill, but the results were spectacular within just days! It is also noteworthy that this tank has a center brace, yet there is no noticeable shadow

There are mixed reviews on the older generation larger units such as the Solaris and earlier TMC LEDs as well when compared to MH light fixtures. I personally did not find LEDs practical for Reef or Planted Aquarium Lighting until 2008.
However the newer ZetLight, Aqua Illuminations, Ecotech Marine, and especially the 3rd -4th generation TMC AquaBeam are a vast improvement in price and PUR output. In fact at the price of the many of the better LED Aquarium Lights coupled with the 50,000 hour lifespan their actual light cost per hour for comparable output is actually favorable to most T5 aquarium lights (5 year warranty for TMC AquaRay, 1 year warranty for EcoTech and Aqua Illuminations).Product Source: TMC AquaRay LED Aquarium Lighting Systems

As I noted earlier, not all emitters are equal even with the open source Cree emitters, commonly sold for other applications; these are only as good as their correct wavelength output (Kelvin Temperature/Nanometers). One cannot compare a computer that uses an exclusive patented Intel processor to one that uses maybe a similar, but generic version of this processor. As with a computer processor company, an LED emitter manufacturer is going to have exclusive patents as well as generic versions.

The exclusive "patent rights" Cree & Osram Olson Emitter bins used by Tropic Marine Center AquaRay AquaBeam & GroBeam should not be confused with CRee emitters sold for other generic lighting applications, as these do NOT produce the best possible Kelvin/Nanometers of Light energy required for delicate marine reef inhabitants and freshwater plants as the newest generation of Cree emitters.
What is also noteworthy is the latest patented version of even the newest Cree emitters (such as the XT-E, XB-D, & ML-E) are not available over the counter to even to the majority of LED builders (including AI or EcoTech) that do NOT have the patent rights.
This is NOT to say that a cool white XT-E emitter used in say an EcoTech Radion Pro is junk, far from it as this is a newer emitter bin. One of the differences between the generic emitter bins and the patented emitters is that the generic bins are in common light Kelvins used by the lighting industry in general such as "cool white" & "warm white".
As an example, the Cree XT-E Cool White used in the AI Hydra FiftyTwo is a new generation Cree, BUT still a common binned emitter that is used for applications ranging from kitchen lighting to industrial light to your aquarium LED; in other words NOT SPECIFICALLY designed for aquarium reef use!
The exclusive patented bins of the XT-E include one that is specifically altered to 10K and therefore is more efficient at reaching required PUR (not PAR) than using a shotgun approach of generic emitter bins (albeit the newer bins).

Far worse yet would be the cheaper no name emitters used by manufacturers such as BaiSheng, Epistar & others and sold under a plethora of other names for so-called aquarium use; these use daylight emitters that can vary widely in Kelvin Color output from only 2000K to 6500K and are in reality totally useless for aquarium use other than just plain light!
Think about why a CFL 10,000K daylight is so much different and more expensive than a common household CFL sold in hardware stores, or the many decorative LED aquarium lights or even those for home or flashlight use; try using one of these to grow your delicate coral or plants (the answer is they will not). This is the reason most earlier LED aquarium lights were not adequate for supporting life properly until about 2008.

Based on email I get, forums I regularly read, & YouTube videos (for DIY LED Aquarium Lights), many seem to make this very INCORRECT assumption about emitters, drivers, PWM, wasted heat energy, etc.
This has resulted in a plethora LED lights flooding the market that are non reef capable, marginally reef capable or very reef capable, BUT often requiring 3-4 times the input wattage for = PUR!
It is not that many of these LEDs cannot keep photosynthetic life; these are simply VASTLY less efficient due to wasted heat energy, use of green/yellow and/or less efficient binned emitters, or use of current reduction vs. PWM; QUITE SIMPLE!

These same older generation emitters, controller technology & drivers are the reason I did not recommend LEDs of ANY brand for "higher-end" aquarium applications until 2008 (readers of this VERY constantly evolving article in 2007 would note this too).

As noted earlier, another common LED emitter usage is "cool white", "warm white", and "neutral white" by many LED manufacturers so as to obtain necessary PUR and a pleasing color through a shotgun approach.
These same LED manufacturers then disguise their LEDs using "cool features" to sell these otherwise inferior LEDs as per PUR delivered for wattage used.

Unfortunately good marketing has convinced many that would never place a "warm white" or "cool white" fluorescent or MH over their reef tank that these lights are top notch (which of course simple logic says they are NOT)???
Green, Yellow, and Red emitters are also employed by some LED lights marketed for Reef applications. The important FACT (as noted earlier in this article) is the green light energy is useless for Zooxanthellae photosynthesis and these same photosynthetic marine life have adapted to an environment of much more blue nanometer bands of light energy and little red is required nor does it penetrate!

PAR readings based on high wattage inputs are often used to promote these LEDs, however the VASTLY MORE IMPORTANT PUR parameter is often far worse in these LEDs.

Sadly many otherwise excellent reef forums seem to fall for some of these gimmicks while ignoring the FACT many use warm/cool white emitter bins, as well as not utilizing Pulse Width Modulation for controlling emitters and waste energy as heat.I am also rather confused when these SAME forums that will recommend LEDs with warm white or cool white emitters, would NEVER recommend these kelvin ratings in a T5 or CFL light??

The end result is many of these albeit reef capable LED fixtures require 120 watts of input electricity to produce the SAME PUR as a 30 Watt AquaRay AquaBeam Ultima due to lower output non patented emitters, use of warm white, green, etc. emitters, and the use of "Current Reduction" (rather than PWM) which along with other circuitry design issues expend more heat energy that could be going to light energy.
In electricity alone at the average USA cost of .13 per kWh, run at 12 hours per day this 90 watt difference equals a $51 savings in just ONE year!!

Add in the lower lifespan and 1- 2 year warranties compared to 5 years and these are not the bargain that they may seem over the long run.

Another misunderstanding about LED emitters is targeting the responsive wavelength. While exact coral responsiveness wavelengths are unknown, much is known in a more broad sense (and even more knowledge is growing, such as the "blue band" of coral responsiveness). For example, we do know that much of the yellow and green bands are useless for most photosynthetic corals, clams, etc.

This has been a controversial topic in a few fragging circles, when it comes to a few red corals such as Red Acans. I have found little to support the claims that these corals fade to orange under correctly applied LED Lights.
That said, while some have proposed that a lack of lower blue nanometer light output is the problem, since I, nor others I trust in my research have witnessed this phenomenon, I put forth that it is a missing photopigment (phycoerythrin) found in cyanobacteria which is living in symbiosis with the coral host (Ref: Mazel et al., 2004).
Since many over load on blue emitters, and admittedly most "better" LEDs lack as much of the yellow nanometer light cyanobacteria need to thrive, I feel this (along with specimen placement) is the possible cause and why those who use a good mix of LEDs or even LEDs with T2s or T5s have not observed this phenomenon.

It is noteworthy that many other LED lights now on the market such as the Marineland Double Bright, SkyLED, or "Ecoxotic Stunner" are only for adding highlights and supplemental lighting, NOT as a primary lighting source other than the most basic of fish aquarium.
This also is the case for the many submersible LED lights that are also available in stores or the internet.

The graph on the left shows the daylight emitter output of the popular Marineland Double Bright 1 Watt 6000K emitter versus a 2012 Marine White XR-E emitter fixture (please click on the picture to enlarge).
This graph is very clear that there are little of the near infrared spikes required for PAR/PUR, only blue and more wasted green/yellow visible light when compared to the NOW OLDER generation Marine White XR-E.

The bottom line is the results of top notch emitters such as the patented Cree & Osram Olson emitters speak for themselves by professional Reef Aquarium Maintenance companies, the National Oceanography Centre, Quality Marine and others.

Use of LED to prevent Red Slime
Another positive attribute of LED Aquarium lights as per s recent study (August of 2009) is that LED used in marine aquariums that suffer with Marine Red Slime Algae (Cyanobacteria) can immediately eradicate Red Slime algae when used in a full spectrum lighting configuration. These "immediate" results were just two weeks.
Reference: Red Slime Algae, Cyanobacteria

*PAR LED Lights are another newer innovation. These high PAR 6500K LED lights come in many different configurations of varying number of emitters.

This LED was originally developed for the Hydroponics/ Plant Nursery Industry but has now crossed over for aquarium use. This LED produces very high amounts of useful lumens in the peak PAR with almost no wasted yellow or green light, making this an excellent and more economical choice for planted freshwater aquariums (& even marine aquariums too, especially those under 24 inches).
This light is very focused with little spread, making it ideal for intense bright spots, but less than ideal for lighting vast areas of an aquarium. The other unique feature is this light is simple to install via a common household incandescent fixture.The picture above/left shows a PAR 38 6500K Daylight over half of a 40 gallon aquarium, demonstrating the high lighting capabilities of this more affordable, yet high output LED.

*LED Summary;
The bottom line is when you compare an LED Aquarium light to the many popular CFLs and even T5s in terms of lumens per watt, focused lumens, PAR, PUR, lower wasted yellow/green light energy, low heat output, energy consumption, long life (25,000 to 50,000 hours vs. 8000 hours), the modern recent generations of LED Fixtures are generally the best available aquarium light.
This includes the patented emitter ultra premium high PUR per watt AquaRay AquaBeam or GroBeam LEDs as well as the still VERY capable Aqua Illuminations, EcoTech Radion, ZetLight (aka Maxspect), and few others.
Most premium LEDs are a better light even in long term cost since (as an example) a 12 Watt Aqua Ray GroBeam 6500K daylight (either #600 Strip or Mini #400 Tile) can easily replace a up to a 80 Watt power compact (also daylight) when you compare ALL aspects of lighting as presented in this article.

When compared to even older T8/T12 aquarium lights, a forth generation TMC AquaBeam & GroBeam High End LEDs require only 15% (or less) of the wattage for the required light energy of a planted or reef aquarium.
This is as little as .6 watt per gallon for high light planted aquariums and .8 watt per gallon for Reef for the TMC AquaRay and 1.25 -1.5 watt per gallon for the ZetLight, EcoTech & Aqua Illuminations, and 1.75 -2.25 for many other LEDs such as the Ocean Revive, Taotronics, etc. (Acroporas may require a higher wattage input per gallon)

Any flaws of LED aquarium lights are quickly disappearing and based on the energy savings for the premium high PUR LEDs with PWM technology as compared to MH.
In fact for Planted Freshwater the top LED Lights (with the highest PUR) have few limits in their applications.

Retrofit is also not all that difficult with most better LED systems sold with hardware that makes DIY mounting options quite varied.
TMC has an optional mounting system of rails and other parts that expands these mounting capabilities even further while the ZetLight & Maxspect come with a built in mounting system for aquarium rim mounting.

LED Light systems are easily complimented with T5 Fixtures, T2 fixture for smaller applications, or even the SHO self ballasted high output CFL for large tank applications.

Finally;, I should note to newer readers of this constantly evolving article that may think there is bias toward high end LED lights, you would only be 1/4 correct, as first I do not recommend the plethora of junk LEDs commonly sold and as well if you were to read this same article circa 2007, I did not recommend ANY LED Light, however technology had increased considerably in this arena of aquarium lighting.

*Lunar (Moonlights)

Often LED as noted above are used as lunar or moonlights. This is an area where anecdotal information seems to be the main information available.

This includes the common belief that moonlight should be "blue" when in truth all the moon does is reflect diffused sunlight back to the earth (more during full moons, less during other phases). Dust or moisture can affect the color spectrum seen by the human eye as well (which often makes the light appear blue).
This means that a dimmed/diffused daylight is a more accurate production of moonlight. This can be done by fading a Reef White AquaBeam LED as an example.

Essentially these are very popular for marine reef aquariums for both a low level "night light" and for simulating moonlight for corals and coral propagation.
Where some of the misinformation comes into play is that many will state that fish need these lights, of which there absolutely no scientific proof and also that corals need these for proper growth which also has no scientific evidence to back this up.
Aquarium Moon lights (lunar lights) do nothing to aid in this.

What lunar lights (moonlights) could do with correct programming for the marine reef aquarium is to simulate marine lunar cycles which are necessary for some fish and coral reproduction/propagation, as Corals in the Great Barrier reef spawn 3-7 days following the first 2 Full moons in late spring and early summer. Even here there is still a lot of controversy as to what cycle is best and how much light is best.

From what I personally have observed combined with the opinions of other aquarium professionals is the use of gray nylon filter placed over standard daylights (T2, T5, T8 CFL, etc.) can work as a moonlight; even low level "white" lights such as nightlight bulbs, or even the Rio Mini Sun LED lights can work just fine for this since this has shown to be a more of a low level light issue and timing issue.

Adding or subtracting the amount/intensity seems to be the secret of simulating these cycles which can be accomplish easily either manually or with electronic timers (that can be set to more accurate monthly 29.5 day lunar cycles of lighting). Strategically placing these lights also shows evidence as to properly simulating this effect.

Please click on the picture above/left for a larger animated version of the lunar cycle

If anyone reading this article has good scientific evidence to the contrary (or even to support) what I have just said about the use of lunar lights, please email me on my contact page with these references.

Induction Lighting

Although not a new technology per say, it is new in regards to commercial availability as until recently, new developments have broken down the barriers of costs and technological setbacks, such as EMC interference, lumen depreciation, ability to dim and a useful range of available wattages.

This type of lighting last up to 100,000 hours and is another good candidate to replace Metal Halide Lights. Induction lights do not have the warm up times of MH or similar (20 second warm up vs. 10 minute warm up), use no mercury, have no filaments to burn out, and they produce half the heat (160 F vs. 300 F for a 200 watt Induction Fixture vs. a comparable in output 400 watt MH fixture).

Induction Lights generally have a high CRI of 82 with a high lumen per watt output (surpassing most MH).

Currently the main negative as per Aquarium use is that Induction lighting is only available in 5000 K Daylight vs. a better 5500-6700 K Daylight, although this is still a viable Kelvin temperature as per PAR especially when one considers the high output delivered with half the heat output.

*HID Xenon

HID stands for "High Intensity Discharge", this technology is currently used in high end luxury cars, however there may be aquatic implications here in the future as PAR and other potential issues are worked out. HID lights use an electrical charge to ignite xenon gas (a colorless, heavy, odorless noble gas, which occurs in the Earth's atmosphere in trace amounts) contained in a sealed bulb. The technology of HID automotive lamps is similar to that of common vapor-filled mercury vapor street lamps.

These Xenon HID lights seem to produce much in the lower chlorophyll A segment of PAR, but currently not as much in the higher infrared part of PAR.

Important Parameters to consider when choosing a light for your aquarium (not a complete list):

Watts per gallon,

Lumens per watt,

Lumen focus

PAR (often easiest determined by Kelvin output), although it is important to note that the symbiotic zooxanthellae found in many corals and clams require more of the "blue spike", so high PAR for higher plants is not exactly the same for corals although it is safe to say a PAR reading of 50 mmol will work for most light sensitive corals.

PUR/Useful Light Energy, probably the most important parameter.
Light energy should not wasted in a high percentage of yellow/green light spectrum that green plants and zooanthellic algae reflect

Output in relation to bulb length (this is where LEDs and to a lesser extent T2s and T5s excel).

Lux, I generally only consider this parameter in deeper Reef and occasionally deeper planted freshwater aquarium to determine if I am getting the proper light where it needs to be.

Specimen Placement/ Tank Depth; although not a parameter per say, it still affects lighting decisions and even the few "watts per gallon" generalizations I provide in this article.
For instance any SPS/LPS coral placement deeper than 18-20 inches should rule out most T5 lights and deeper than 24-30 inches rules out many LED lights (24 to 30 inches at least requires the most powerful LEDs such as the AquaBeam 1000 Ultra Reef White or Orphek Nilus Reef LED Light); In these deeper depths the Metal Halide is still king

The watts per gallon is part of the lighting equation as stated above is highly inaccurate when taken by itself, yet may in the aquarium hobby industry still go by this outdated generalization which leaves me scratching my head with all the advances in lighting technology. Taken together, the first FIVE points are the most critical (which does include watts per gallon), but no one of these should be a sole determiner of the lights.

Even a "105 watt Super High Output (SHO) Light" which is an excellent light, especially for planted freshwater or hydroponics applications, when compared apples to apples to the 30 watt GroBeam 1500 Ultima only produces 85% of the same useful light energy despite using more than triple the energy.
This is not to say the 105 SHO is not a good light, far from it, especially when one considers the vastly lower price and that this SHO light still out produces most any T12, T8 and T5 (using 6500K for all comparisons); as a generalization (assuming equal Kelvin) the SHO requires only 2 to 2.5 watts per gallon for a "high light planted aquarium".

Using the high end TMC or similar high PUR LED Lights as a Comparison:

* 20 watt T12 light with a Kelvin temperature of 5000 K,
Compared to a:
*20 Watt LED with an adjusted Kelvin temperature of 6500 K.

The "watts per gallon rule" would certainly require at least four of the 20 Watt T8/T12 grolite while this same 20 gallon freshwater aquarium would only require ONE 12 watt TMC GroBeam 500, this is .15 of the required wattage or about .60 Watts per gallon.

For reef applications using high end LED emitters only, not Marineland Single or Double Bright, Ecoxtic Stunners, etc., I would suggest about .8 to 1 watt per gallon; so two AquaBeam Reef White LEDs would be my suggestion for this 20 gallon aquarium (generally speaking, four high end 12 watt LED Light fixtures such as the AquaBeam Reef White 600 would work well for a 60 gallon reef based on this example).
Of coarse the differences can vary, so even this comparison only works for the described lights and tank, this is also based on the newer Cree and Osram Olson Power LED emitters employed by TMC (and similar proprietary emitter bins developed by Orphek as well as some PAR 38 LEDs) which have a high output of useful energy.

In fact based on raw data from controlled tests, even the modern comparable Kelvin HO T5 lights or Metal Halide which are so popular do not hold up in comparison to a modern LED with the Third Generation AquaRay LED emitters. This data indicates that a modern LED requires 14-28% of wattage for the same useful light energy output.
Even then a T5 or even more so a T2 are vastly superior to the older style aquarium lights when all criteria are applied (SHO as well are also superior).

Note:Regular readers of this article will note that I changed/simplified my above formula. While the previous formula was always intended as an example (not a hard & fast rule/equation) and those that read this entire article in context could easily figure this out; however one of my aquarium/reef professionals who regularly proof reads this article could see how a reader could take this out context if they were to not read this article in full context (as I pointed out to him as per one extremely rude & condescending email).
So as per his suggestion, I removed this formula and replaced it with the above suggested more simplified example of why the "watts per gallon" formula does not apply to most modern aquarium lights.

Lighting Time & Replacement

Here is a summary of lighting requirements for different aquarium types. I recommend timers for any aquarium to provide good daylight/night cycles, however this is even more important with Planted Freshwater and Saltwater Reef or Nano Reef tanks. Turn the actinic lights on about one to 1/2 hour ahead of the daylight bulbs and one to 1/2 hour later in the evening.
I generally have the brightest lights on for about 12 hours per day, with 1-2 hours of less bright or "ramping" up or down of LEDs if used. Sometimes with MH I will have them in a third cycle that is on for only abut 10 hours or less.
For LED moonlight settings, generally just a 1% power setting is sufficient between main lighting cycles. If you have separate moonlights, I would run these 8-16 hours (I have yet to find in benefit from this that can be scientifically proven other than aesthetics).

Replacement;ANY fluorescent light used for aquarium applications such as planted aquariums or reef, slowly burns up phosphors and other rare earth elements that produce the light energy necessary for PUR.
As with a UVC bulb/lamp used for a UV Sterilizer, these lights go through a "half life", meaning that a light that is run 12 hours per day that may last 2 years (as per rated life) should be actually replaced every year otherwise these lamps are running at 50% and less of initial light energy production and then often producing much more yellow light that is inducing to more algae and cyanobacteria growth in particular.Product Resource: Aquarium UVC Bulbs/Lamps

The picture to the left clearly demonstrates the difference we can see with just our human eye between new 6400K Daylight SHO and one nearly two years old.
The color temperature of the old lamp/li

Light (Lamp) Placement:

Pendant vs. Canopy with Reflector (Mirror, Aluminum, Mylar)
The advantage to a pendant reflector over a canopy with reflective backing (mirror, aluminum or mylar reflector) is that it will radiate downward in a slightly more magnified fashion than a pendent reflector, however the reflector/mirror has one advantage over the pendant and that is more wide spread light distribution. A pendent (such as an SHO or Metal Halide) or LEDs hung on rails over an aquarium allows for an open tank which allows for more light energy to reach the tank. The negative is evaporation and possibly aesthetics (which of coarse comes down to opinion).

If lights are placed in a canopy (which in my opinion looks better) it is generally best to keep a lid on the tank to prevent too much moisture from building up inside the canopy which can also damage lights. I recommend venting the canopy and adding a small fan in at least one of the vents aimed to push air out. This will help cool the inside of the canopy/hood and, just as importantly, help expel moisture. With low heat lights such as LED and T2s, this is of less importance especially for heat, but still helps protect lights from moisture damage.

The use of a reflector such as mylar (even heavy aluminum foil can work, although it tends to degrade from salty moisture over time in my experience) protects the canopy wood from heat and is useful for directing light downward, especially if SHO, T2, T5, or Compact Fluorescent lights are used. BTW, my first choice is Mylar for both reflective properties and longevity. Please the picture in the T2 Light section of this article for a canopy using Mylar.

The use of lids (glass in particular) does block light energy and gets buildup quite quickly under the lids (although lights exposed to open tanks need to wiped clean often too), however the choice of lid can minimize energy loss (see the section lower in the article under Marine Light Summary for more about lid choices).

So this choice comes down more to aesthetics, space, personal preferences, tank arrangement of plants or corals and more.

Light Penetration

What is often a bigger issue, especially with deep tanks (over 24 inches) is to allow as much of the blue light (which is found as part of the light spectrum of high PAR Daylight 6400 K lights) as possible through to the tank and often a glass top will block these light rays (over 60%) so using polycarbonate or no lid at all may do more for effectiveness than whether you use a mirror or pendent (see further in this article for more on this subject).

As well for tanks over 24 inches the use of some higher Kelvin in your light "mix" may be necessary for coral tanks or in some cases high light requiring plant tanks (depending upon the environment being replicated, as a high tannin, often shaded Amazon River tanks would not require the light intensity and higher Kelvin output of a Reef Tank).

The use of 14,000 K MH (or even higher Kelvin 20,000K MH) or AquaBeam Reef White 18000K LED in a mix with High PAR 6400 K SHO lights may provide the "mix" necessary for deeper freshwater tanks.

For Marine, even in tanks under 24 inches, the use of actinic blue lights may help provide the correct PAR/PUR to specimens lower in your tanks water column.
As an example, a Reef Blue or Fiji Blue LED may also help provide this.

With the above noted, do not make the mistake of going over board with blue light in a relatively shallow aquarium.
While an aquarium at 20 inches with ANY man made light is not going to compare to an ocean reef at 20 inches with sunlight, adding 2 to one blue to daylight (as some LED brands or users have done) or all 20,000K lights is not the answer.
See: PUR versus PAR in Aquarium Lighting; Including Spectrographs

Here is the general light spectrum absorption of water:

Only 73% of the surface light reaches a depth of 1 centimeter (less than a half inch)

Only 44.5% of the surface light reaches a depth of 1 meter (3.3 feet)

IMPORTANT- Another point about lighting in general is that lower PAR wave lengths of light such as "near" UVA (400-485nm) do not penetrate glass well.
I recommend direct lighting (best), quartz, Plexiglas (acrylic), or polycarbonate (Lexan) to optimize PAR light penetration or in particular where near UVA is important.
Just make sure to clean your bulbs, Plexiglass or polycarbonate tops regularly to prevent build up that will block light. Even though infrared will penetrate glass better, it will not penetrate dirty glass with algae or hard water deposits on it, so keep your aquarium cover clean for any tank where lighting is important such as FW plants or Reef Aquariums.

Here is a very basic breakdown of PAR Spectrum blocking potential:

Glass- about 25% will be blocked

Acrylic- about 10%

Polycarbonate- about 15- 18%

Quartz- about .5-2%

Here are a few light transmission graphs:

The last graph compare 6 different grades of Plexiglas as per UV transmission, with the 'G' being the best candidate for the widest aquarium applications. However my understanding is that the GUVT is used by most acrylic aquarium builders.

Specimen Placement

This is an important consideration that is often missed or not enough weight is given to this part of aquarium lighting and aquascaping

Reef: Another important point that is often missed by many reef keepers (usually newbies) is even with newer technology high output lights (such as a MH, LED, HO T5, T2, or SHO), specimen placement can make or break a good light system.

As per the previous section as to general light absorption of water, you may need to move certain corals or other light sensitive reef inhabitants as high up in the water column as possible, this is especially important with SPS corals (short polyp stony corals) where placement on the rocks directly under your lights is even more essential.
This is not as essential with LPS corals (long polyp stony corals) since they are more commonly found in near the sandy lagoon bottoms.

You may find that you will have to move corals around to find a "sweet spot" in depth, this includes when changing lighting types.

Sometimes in conversations with reef enthusiasts that are questioning different lighting systems/ideas is that it is often missed that the most high light requiring corals (such as SPS) do not grow 50 feet (15 meters) below the surface in the reefs and that these corals will be just below the surface, so regardless of the lights you choose, placement is extremely important.
Even less light demanding tropical reef building corals species are restricted to the euphotic zone, the region in the ocean where light penetrates to a depth of approximately 230 feet or 70 meters (there are cold water corals that grow in deeper water, however these are not the reef building corals kept in aquariums that secrete calcium carbonate).

I should also note that with SPS corals in my own experience, that placement low or even in substrate that I have observed the corals getting "eaten away" by bacteria from the bottom up; while this is an anecdotal observation of mine (as other factors were not tested in a controlled scientific study), it is still consideration in coral specimen placement.
The bottom line is that you can have the best lighting system that money can buy, but poor placement of specimens can make it all for not.

Another thought as marine tanks in general, is to consider what type of environment you attempting to duplicate; for instance a Reef Tank set up to duplicate the Great Barrier Reef would require aquascaping and higher power lighting to best replicate this environment.
While a marine tank set up to replicate the much more turbid waters off the California coast would not require the same aquascaping or as high power of lighting.

Freshwater: If your lights are for Freshwater plants, I would move the high light requiring plants directly under the lights (I generally elevate them with terracing, which can look quite attractive if done well and serve a dual purpose of aesthetics and better light energy absorption).
Reference: Freshwater Aquarium Plant Care, Information

As with marine tanks, consider the environment you are replicating; for instance an Amazon River environment aquarium (with fish such as Discus) are full of tannins and have many shady areas and so one cannot compare the lighting needs of a tropical reef with the Amazon River. More light and dark spots should be utilized so as to provide a more natural and comfortable environment for your aquarium inhabitants, as well the same intense lighting for the same size Tropical Reef tank should not be used for an Amazon River aquarium of the same size and depth.

TANK SET UP LIGHTING SUGGESTIONS:

Please note; the AquaRay LED is used as an example, other 'high end' LEDs such as the ZetLight, EcoTech, AquaIllumination, Maxspect could be substituted, although please note that generally these before mentioned LED usually require about twice the wattage for the same results as noted earlier in this article as per the KNOWN science of PUR, Energy Loss as heat energy, and PWM.
Some economy model LEDs will require even more wattage, such as 2- 2.5 watts per gallon for a Reef Aquarium for the EverGrow LED

Please note that I have received many requests for exact recommendations of lights for certain aquariums. I prefer to not give these as there are too many variables which then will make my advice anecdotal, as with Aquarium Medications, Chemistry, & similar subjects I prefer to give as many tools for the aquarium keeper to make an educated decision on his/her own. As well since Lighting is a fast changing part of aquarium keeping, a recommendation I make today may be less accurate in a year (or less).

As a guide I made a few suggestions in the previous tables based on a 20 Gallon, 60, & 100 aquarium (hopefully readers can extrapolate their aquarium recommendations from the aquarium size that is most similar to theirs.

*With each example I break it down to aquarium keeping types.
*As per "Light Type", I will provide T2, T5, T8, CFL, SHO, MH, & LED (with LEDs, this will ONLY mean high output (HO) LEDs, not the plethora of low end LEDs such as those marketed by E.Shine of China)
*With mixes of lights whether LED with T2 or T5 OR all LEDs with Daylight and Reef Blue, you can stagger on/off times such as blues (actinics) coming on 1/2 to 1 hour before the daylight and off 1/2 to 1 hour after daylight (such as 10-12 hours of daylight and 12-14 hours of blue).

Please take these only as suggestions, NOT something written in stone. In fact, there are so many variations that can come together for the best lighting to fit your aquarium needs (think of how 2+8=10 as well as 4+6=10; in other words there are many options, including mixing and matching to reach the same goal of correct lighting for your aquariums specific needs)

Some will note that some of the LED lighting suggestions are MORE than the .8 or .6 watts per gallon we suggest elsewhere in our articles (Ditto for other lighting types). The reason for this is that while the .8 watts per gallon is enough HO LED light for your tank, it may not cover your tank entirely, leaving some dark areas. This is why you will find more light suggested here versus elsewhere.

Please consider all I have written up to this point, your personal aquarium parameters, exact inhabitants, budget (which is always important), & more when deciding what lighting systems or combinations there of to use.

SUMMARY:

The reader should note from all the information written above, that when deciding what lighting to get for your aquarium that the watts used is only one third or less of the equation in deciding what lights, what size and how many should be used. I will admit that I still will use the watts per gallon as a starting point with SPECIFIC lights comparing apples to apples; however specimen placement or tank depth, lighting type strengths and weaknesses must be considered too.
Do no compare apples to oranges; such as SHO to T12, or High Output LED to low output LED such as Marineland LEDs. Or even comparisons of a super premium high PUR per wattage input LED to other high end LEDs but that still require a higher input wattage for the same results due to energy loss as heat, less than optimum PUR, use of current reduction technology instead of optimum PWM technology (example the AquaRay AquaBeam to the still excellent but higher wattage requiring Maxspect and ZetLight LEDs)

Please note that besides years of personal fresh and saltwater keeping experience, MUCH more of this information I have written here comes from research OUTSIDE the aquarium industry. Much of what I have learned (and I am STILL learning) comes from this constant research of as many lighting tech research as I can read often from horticulture or other outside sources as noted earlier.

Some examples include the lack of information in the aquarium industry/hobby that must be found elsewhere includes the SHO or T2 lights that are often superior to more commonly recommended bulbs in the aquarium hobby, yet in much better funded lighting and horticultural industry literature/information these lights are much better known.

There is also good evidence that correct lighting benefits ALL fish as well, including salt & freshwater fish. I have observed better disease resistance in marine fish in loosely controlled studies when lighting is upgraded to higher intensity, high PAR/PUR lights. Proper lighting may play a role in nutrient assimilation, improved Redox, lower incidence of Brown Diatom Algae. Studies in humans that show an impact of lighting on health, may have strong implications for fish (this may be a factor in my studies that showed higher disease resistance when lighting is improved).
Reference: The Importance of a Balanced Redox on Fish Health

Lighting that as closely duplicates the sun (not necessarily light that is most pleasing to us) is important for ALL life, although more noticeably for corals and plants. Fish too are part of this chain of life. Basically if you take away the sun and the energy it provides, you take away life itself and I do not think if you are trying to achieve the best environment for your fish whether fresh or saltwater, you are doing them a favor by depriving of this source of energy, so duplicating this is one more part of your "aquarium keeping puzzle".
Reference; "Aquarium Disease Prevention".

I should point out that obviously, some fish prefer subdued light, but this is easily handled by hiding places, caves, plants (live or artificial), products such as Peat, Pillow Moss, or Indian Almond Leaves that "color" the water, and simple placement of lights where as some areas of the aquarium are better lit than others with plants/corals placed in way that benefit the most in these areas.

As I noted earlier, I am STILL learning after being in the hobby since the late 60s and professionally employed in the aquarium industry since 1978. BE WARY of anyone who will shoot down the science that is explained here because it does not fit their view and the fact that they are unwilling to learn.
What is amazing to me, is that often many simply confuse what they like with the known facts of science.
Example; just because you might like green and yellow LED emitters, does NOT mean that this light energy, often measured in PAR values actually counts toward much if any of the useful light energy an acropora coral or aquarium plant requires!! If you like this light fine, but this does not change the known facts of lighting that this is mostly useless light.
Another act of scientific malpractice I have often noted is the simple fact that energy lost as heat is energy that is not going to light energy, which all lights are guilty of, but to widely varying degrees, yet many choose to ignore this most basic principle of science when comparing lights.
FINALLY, another example would be moon or lunar lights. I myself prefer blue lights for this, as have most of my clients, but this still does not make moon light blue, as the facts are it is NOT!!

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