Light fixtures (i.e., lights) utilizing high intensity discharge (HID) lamps, such as mercury vapor, metal halide, xenon, high pressure sodium (HPS) and low pressure sodium (LPS) lamps are well-known in the lighting field, and are currently in wide use for area and road way lighting applications in a variety of environments. There are literally millions of these lights in operation throughout the world to light streets and parking lots, industrial spaces, aquariums, gymnasiums, arenas, parks, and many other indoor and outdoor areas. Other types of gas discharge lamps, such as fluorescent, and neon also are widely used in commercial, residential and civic environments. Induction and sulfur lamps are other types of lamps similarly generating light from gas excitation.
A clear arc tube (i.e., a refractory envelope made from, for example, glass, quartz, clear ceramic, etc.) is filled with gasses, such as rare gases and metals. Sodium lamps include an amalgam of metallic sodium, and mercury as a buffer gas for color and voltage control. Small amounts of xenon (or, sometimes, argon plus neon) are used as a “starting gas.” A metal halide type lamp is typically filled with argon along with mercury and other metals (e.g., sodium, lithium, thallium, scandium, etc.) in iodine/halogen salt form. A xenon lamp is typically filled with xenon gas. The specific gas mixture used in a particular lamp determines the characteristics of the light emitted therefrom.
The arc tube is often encased within an outer bulb to minimize temperature variations along the arc tube, to reduce oxidation of internal interconnects, to absorb UV light, and to otherwise protect the arc tube. Main (i.e., operating) electrodes, and optional starting electrodes, are enclosed within the arc tube. A starting voltage from a power source is applied from a ballast across the electrodes. The voltage necessary to ignite the arc in the gases is typically derived from a starter circuit connected across an electronic or transformer ballast. Electrons are emitted ionizing one of the fill gasses (e.g., argon) permitting an arc to be established between the main electrodes located across the arc tube. Heat from the arc causes mercury, and/or other materials within the arc tube to vaporize, increasing metal pressures and resulting in color changes until full output equilibrium is reached. Increased metal pressures cause a decrease in the electrical resistance of the lamp up to some point. Further temperature increases will tend to increase electrical resistance. This start-up process can take several minutes to stabilize.
A fluorescent lamp operates in a somewhat similar manner. A glass tube is filled with low pressure gasses (typically argon or argon-krypton with a small amount of mercury added). Electrodes are located across the tube. The inside of the glass tube is coated or composed of phosphors (e.g., calcium tungstenate, zinc sulfide, zinc silicate, etc.). An electrical voltage of sufficient strength is applied across the tube's electrodes causing electrical current (i.e., an arc) to flow between them. The current is composed of moving electrons which interact with the gas atoms (e.g., mercury) causing some of the atoms to move to a higher energy state. However, these excited energy states are not stable and the electrons quickly drop back down to their original energy levels emitting the excess energy as ultra violet (UV) light. UV light is not in the visible light spectrum. The UV light is absorbed by the phosphors and then reemitted at a different frequency (e.g., light in the visible spectrum). This principle is known as florescence, and different types of phosphors emit visible light at different wavelengths (i.e., colors). HID lamps emit visible spectrum light directly and do not need a coating of phosphors in order to produce visible light.
“Neon lamps” are tubes filled with a variety of low pressure gasses such as neon or mercury vapor (with argon), helium, nitrogen, krypton, hydrogen, xenon, and argon. Colored tubes and/or phosphors are combined with a particular gas mixture and concentration to achieve a light emission of the desired color (i.e., spectrum). They otherwise operate similar to fluorescent lamps.
Induction lamps produce light through use of an induction coil to create a high frequency electromagnetic field inside an electron/ion plasma gas enclosed by a glass housing. The field excites the plasma causing atoms (e.g., mercury) to emit UV light. The UV light interacts with phosphors and is converted to visible light in much the same manner as fluorescent lamps. The absence of electrodes is a beneficial feature of this type of lamp.
Sulfur lamps use a small microwave generator (i.e., magnetron) to excite a gas mixture (e.g., argon and sulfur) in a clear quartz enclosure. The argon gas absorbs energy from the microwaves and then kinetically transfers it to the sulfur molecules, which in turn produce to visible light directly. The atoms or molecules of another type of gas discharge lamp are ionized by a radio frequency in proximity to the arc tube.
The lumen (lm) is the SI unit of luminous flux. A standard 100 watt incandescent light bulb emits approximately 1,700 lumens.
Although lamps have a relatively long lifespan, they eventually fail over time. HID and fluorescent lamps exhibit undesirable behaviors as they approach failure, from flickering (e.g., fluorescent, etc.) to exploding (e.g., metal halide, etc.). As certain HID lamps age, their internal resistance increases requiring higher voltages and currents to start, and sustain, the lamp's arc. Electrode depletion and deposition of the electrode material on the interior of the arc tube darkens the tube, resulting in less light emission, increasing heat retention and gas pressure. Internal resistance increases as temperature rises. Eventually the internal resistance exceeds the voltage and current capabilities of its ballast and/or power supply. The lamp can no longer maintain a continuous arc and ceases to operate.
Prior to complete failure the light may cycle on and off repeatedly, igniting and operating until heating increases internal resistance to the point of shut-off, then cooling down until resistance decreases to a point where the lamp can re-ignite. Start-up time, and the required start-up voltage, increases as the lamp ages. The lamp may successfully operate intermittently, continually flash on then off, or continuously attempt to start without success. This repetitive on/off process is known as “drop-out” or “cycling” and occurs over and over until eventually either the lamp is no longer capable of sustaining an arc at the supplied voltage or some other component of the lamp is damaged (e.g., from high or prolonged starting currents and/or voltages). Cycling can be an indication of a lamp's impending end-of-life. As the lamp ages and deteriorates, the “on” time gets progressively shorter. Cycling can be visually distracting or annoying, especially in residential areas. Electromagnetic noise is generated during arc striking, and cycling can result in communication, radio and television frequency interference.
Cycling is not always easy to detect and correct in a quick and cost-effective manner. Failing HID and other lamps waste energy since ballasts remain energized when the lamp is cycled off. A cycling lamp may remain lit for several minutes or more before it heats up, loses its arc and attempts to restart. This may require a service person to visually monitor individual lamps for more then just a brief period of time in order to discover whether cycling is occurring. This is particularly problematic in outdoor applications where lights are widely spaced from one another. Many of these lamps are owned and/or maintained by utilities or governmental entities that have thousands of HID lamps in operation. Manual lamp observation is labor intensive, and thus not a particularly cost-effective means for detecting when lamps are nearing, or in, the cycling phase of a lamp's life cycle. In addition, cycling is often only apparent at night since outdoor lighting normally does not operate during the day. Light owners typically do not have large numbers of service personnel constantly checking lamps at night. As a result, cycling may continue for extended periods of time and often until someone notices the misoperation, is sufficiently inconvenienced by it, and complains to maintenance personnel. Dispatching maintenance personnel in response to the failure of a single lamp is expensive and inefficient, considering that each lamp will ultimately fail and require its own individually-scheduled maintenance visit. Power supply voltage transients and fluctuations also impact lamp cycling too. Service personnel responding to a reported lamp outage may find that the lamp has since cycled on and not be able to accurately locate the “failed” fixture or decide not to replace it.
Cycling is initially correctable by simply replacing a depleted lamp. However, if a cycling condition is allowed to continue over a period of time, it can eventually damage the lamp's starter, ballast and/or other light component(s). As the lamp's internal resistance increases, corresponding higher applied voltage is required for starting and operating the lamp. Ultimately the lamp voltage can no longer maintain a continuous arc. High currents/voltages can damage or degrade a starter, a ballast, or another portion of the light's electrical circuitry. The damaged light cannot operate and the lamp ceases to cycle. When this occurs, the starter, ballast and/or other component(s) must be replaced along with the depleted lamp, resulting in higher overall repair costs. If degradation to the ancillary portions of the light are not detected when a HID lamp is replaced, a second service call may eventually be required when the degraded component ultimately fails. For these reasons, it is desirable to prevent or stop a HID lamp from cycling.
Simply knowing a lamp's calendar age (e.g., calculated from its installation date) and the average life of a particular lamp type, one could schedule a chronologically-determined lamp replacement prior to it reaching the expected cycling phase of the lamp's working life. However, owners/maintenance providers would be required to maintain accurate lamp age records. And the manufacture's estimate of the lamp longevity is only an average expected value. Each lamp's actual longevity will vary from the average expected lifespan. Many lamps will have a useful in-service life that is greater then the manufactures estimated value. Replacing lamps late will not avoid cycling and the accompanying light component stress. Replacing lamps prematurely will result in increased maintenance costs since remaining lamp life is discarded.
Several conventional methods for detecting and/or halting cycling are known. Conventional methods for detecting cycling typically monitor or test an electrical parameter such as voltage, current, power, power factor, and/or resistance magnitude associated with a particular lamp type, ensuring proper values exist for one or more respective magnitude(s). Conventional methods for halting cycling typically provide an electric or mechanical device to interrupt the lamp's power supply subsequent to detection of cycling or abnormal electrical magnitudes. For example, thermal overload protective devices applied to all varieties of electrical equipment are well known. The shut-down light still requires discovery to initiate repair. Other conventional methods provide local (i.e., at the light fixture) indication of likely cycling conditions subsequent to an abnormal voltage/current/resistance magnitude being detected. Another conventional method utilizes a timer energized when the lamp is on, to track the lamp's accumulated operating time as a refinement on the calendar age tracking method. Another conventional method involves temporarily applying an electrical test circuit to the lamp. These conventional methods still rely on someone noticing the light not operating, or its local defect indication, and may also require the failure indication being reported to the owner/maintenance provider. Due to the large quantities of operating HID lights, conventional methods requiring monitoring components added to each light installation may therefore, not yield a cost-effective solution. Likewise, retro-fitting existing light installations with additional monitoring components would entail substantial labor and equipment costs.
Accordingly, there is a need for a more cost-effective and efficient method and apparatus for predicting remaining lamp life, which addresses the aforementioned issues, as well as other related problems.