1. Field of the Invention
The present invention generally relates to illumination devices. More particularly, it relates to artificial lighting using quantum dots for spaces housing animals.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Artificial lighting is commonly used in the poultry industry, with a number of companies offering lighting solutions, mainly based on light-emitting diodes (LEDs). Studies have shown that poultry production can be greatly improved by the simultaneous management of three conditions:
the color of light;
light intensity; and
illumination time (photoperiod).
In the United Kingdom, animal welfare guidelines state that, when rearing broiler chickens, lighting conditions should meet the following standards:
chickens should be provided with a period of darkness of at least 30 minutes per day;
all chicken houses should have uniform levels of light; and
light intensity should be at least 20 lux at bird eye height.
The photopic response of poultry differs from that of humans, with poultry having the ability to visualise UV light. In addition, poultry have extra-retinal photoreceptors in the brain. Numerous studies have sought to identify the optimum lighting conditions for rearing poultry.
Domestic fowl are quadchromants, with sensitivity to UV (peak at 385 nm), blue (peak at 450 nm), green (peak at 550 nm) and red (peak at 640 nm) light. Their sensitivity to 450-nm and 640-nm light is 12 and 4 times that of humans, respectively. Using a behavioral test to determine the spectral sensitivity of domestic broiler fowl (Gallus g. domesticus), it was found to be highest between 533-577 nm. Two areas of low sensitivity were observed at 415 nm and 600 nm.
In addition to retinal photoreceptors, poultry have extra-retinal photoreceptors in the brain, located in the pineal gland and the hypothalamus. The pineal gland is responsible for controlling a bird's circadian rhythm, while the hypothalamus controls most homeostatic and physiological processes, including reproduction. One study found no significant differences in the effects of different lighting conditions on blind and sighted laying hens, suggesting that light penetrating the skull may influence poultry development.
Lighting for Rearing Broiler Poultry
Broilers are poultry raised for meat production. Studies have shown that the color and/or color temperature of light under which broilers are reared can affect their behavior, body mass and meat quality.
Color of Light
The effects of blue, green, red, and white light on tissue growth and bird behavior in broiler chickens has been investigated. In the study, the birds were able to choose their light environment after 28 days of being in a particular light environment to determine their color preference.
Birds reared in red or white light were more active, displaying greater walking activity in white light and greater floor pecking, wing stretching and aggression in red light. Aggressive behavior was less common in birds reared under green or blue light, and intermediate in birds reared under white light.
After one week of being able to choose their color environment, all birds chose a different color from that of their previous environment. Birds reared in white, red or green light showed a preference for blue light, with green light being their second choice. Birds reared in blue light showed a preference for green light, with blue light being their second choice.
Other studies have investigated the effect of polychromatic light with various green and blue components on the growth and physiology of chicks. Rearing chicks under blue-green light with a depleted blue (30% blue) or a medium blue (50% blue) component resulted in decreased body mass, whereas an enriched blue (70%) component promoted body mass compared to rearing chicks under monochromatic green or blue light. Food intake correlated positively with final body mass.
The effects of monochromatic LED light on meat quality has been reviewed. One study has shown that breast and drumstick muscle from poultry reared under mixed blue-green light has a softer meat structure compared to that of poultry reared under incandescent light. White light has been shown to result in the lowest fat content in breast meat and to improve its amino acid content.
Thus, rearing broilers in blue-enriched blue-green light may potentially offer benefits such as improvements in bird behavior, increased body mass and improved meat quality.
Color Temperature of White Light
A previous study found that when rearing poultry under white light, color temperature influenced bird behavior. Broiler chickens were reared in eight different light environments, comparing four light sources, each at two different illuminances. The light sources tested consisted of:
fluorescent tubes with a correlated color temperature (CCT) of 6500 K;
a spectral sensitivity-matched light source;
incandescent bulbs; and
warm white fluorescent tubes.
Light intensities of 5 chicken lux (or “clx”—a measure that takes into account the spectral sensitivity of chickens) and 100 clx were investigated.
At one week of age, the broilers showed no preference for light source, but by six weeks of age, they showed a preference for 6500 K light or warm white light, the two illumination sources closest to daylight. Light source affected feather-directed behavior and object manipulation. Illuminance was found to have little effect on bird behavior.
When reared in their preferred light environment, broilers displayed more feather-directed behavior (preening and pecking), object manipulation and foraging in 6500 K light than in warm white light.
Taken together with the results from the study wherein birds showed a preference for a blue- or green-light environment, overall, the studies suggest that rearing broilers in either blue-green light or cool white light may have a positive influence on animal welfare.
Lighting for Rearing Laying Hens
Lighting color has been found to influence the sexual development and consequent egg-laying performance of hens.
In a study of the effects of colored light on egg-laying performance, laying hens were kept under white, red (640 nm) or green (520 nm) light for four weeks after two weeks under white LED light. Red light resulted in accelerated sexual development and superior laying performance when compared to hens maintained under white or green light, which showed no differences compared to one another.
The influence of light wavelength on reproduction, growth and stress of laying hens has also been investigated. Cages were fitted with LED strips providing pure green (526 nm), pure red (632 nm), or white (red, green and blue) light, set to 10 lux. Red and white light resulted in higher concentrations of the sex hormone oestradiol in hens, indicating stronger ovarian action. This, in turn, resulted in a significantly lower age at first egg production, compared with green light. Hens reared under red or white light also had a longer and higher peak egg production and higher cumulative egg production than hens reared under green light. The study compared blind to sighted birds, finding no significant differences. This suggests that extra-retinal photoreceptors may be stimulated by longer wavelength (red) light that can more easily penetrate the skull than shorter wavelengths of light.
The results of the studies suggest that rearing laying hens in a red light-enriched environment may be beneficial in terms of stimulating egg production.
The results of the studies concerning artificial poultry lighting suggest that white light may not be optimal for poultry welfare and development, and that it may be of benefit to rear broilers under different conditions than that for laying hens. While cooler white or blue-green light has been found to be of preference and benefit to broilers, sexual development and egg-laying performance is enhanced when laying hens are reared under red light. Given the preference of poultry for blue or green light, a lighting system comprising white or blue-green light with an enhanced red component may provide a balance between egg production and animal welfare for rearing laying hens.
Prior art solutions to animal lighting have used monochromatic light sources, either alone or in combination, as well as sources of white light. Using these methods, the wavelength(s) of light cannot easily be tuned during animal development. Studies have shown that different wavelengths of light provide superior results at different stages of animal development. Thus, there is a need in the art for a tuneable light source that can be manipulated to emit different wavelengths of light during different stages of animal development.
Lighting for Aquariums
Other artificial animal environments may benefit from the color selection ability provided by light sources that comprise quantum dots—for example, aquariums.
Aquariums typically employ either LED lights which use multiple LEDs that emit different colors to provide a range of different overall light colors or fluorescent tubes which produce broad-spectrum light but only last for about six to nine months before beginning to fade (which can lead to algae growth—a real problem for aquarium owners). The use of an appropriately tuned quantum-dot-based light source can both promote photosynthesis and also provide the best display colors for the fish. These features, combined with the superior lifetime and low energy consumption of LEDs, provide an attractive alternative to the current use of fluorescent tubes.