HID Track Lights
Track lights provide directable beams of high-quality light for use in retail displays, galleries, museums and high-end residences. They are useful in locations where lights need to be aimed at different angles and where the position of the light may be changed frequently. Until recently, the only light sources that could provide the right kind of illumination for track lighting were inefficient incandescent lamps. The introduction of low-wattage, high-intensity discharge (HID) lamps in the mid-1990s, however, gave designers and specifiers an energy-efficient alternative. These lamps not only reduce energy use but last several times longer than incandescents, thus leading to reduced lamp-replacement costs as well. However, lamp and fixture costs for HIDs are significantly higher than those for incandescent units so HID products are most cost-effective in applications with long burn hours and where changing lamps is difficult.
What are the options?
Lamp types. Two kinds of lamps are available for HID track lights: metal halide (MH) and high-pressure sodium (HPS). Both offer increased efficacies and longer life in comparison with incandescent options—albeit at a higher price (see Table 1).
| Table 1: Comparing halogen, metal halide and high-pressure sodium (HPS) lamps | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| For track lighting, metal halide lamps offer the best combination of efficacy, lamp life and colour quality, but at a higher price than the halogen lamps most often used. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Halogen | Metal halide | White HPS | General-purpose HPS | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lamp efficacy (lumens/watt) | 15-35 | 50-100 | 30-50 | 50-90 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lamp life (hours) 2,000- | 2,000-4,000 | 7,500-20,000 | 7,500-16,000 | 16,000-24,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Colour rendering index (CRI) | 100 | 65-93 | 80-85 | 60-65 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lamp cost ($) | 10 | 50 | 120 | 20 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fixture cost ($) | 60 | 300 | 300 | 300 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Source: E Source; manufacturers' literature | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MH lamps, in which certain iodides of metals are added to the old-style mercury vapour lamp, use one-fifth to one-tenth as much energy as their halogen counterparts and last three to five times as long. However, their colour quality is not quite as good.
HPS lamps, which contain a sodium amalgam that is vapourized to generate light, are available in three grades. The highest grade, "white" HPS lamps, provide colour quality that is better than most metal halide lamps, but not quite as good as an incandescent. However, this colour quality is gained with some sacrifice in efficacy and life: These lamps typically use about half as much energy as an incandescent lamp, but significantly more energy than an MH lamp. General-purpose HPS lamps put out a lower-quality light, but they're almost as efficient as MH lamps. Low-grade HPS lamps are never used in track lights—they offer very long life and high efficacy, but their poor colour characteristics limit their use to outdoor and industrial applications.
For most track lighting applications, MH lamps offer a better combination of efficacy, lamp life and colour quality than HPS lamps. The longer life of some HPS products may make them suitable for applications in which fixtures are especially difficult to access for lamp replacement.
Fixture types. Track lights for HID lamps are similar to track lights for incandescents (see Figure 1). The track can be recessed into the ceiling, mounted to the surface of the ceiling or suspended from the ceiling in a configuration known as a pendant mount. The track head—which includes the lamp housing, lamp, socket and a reflector cone—moves along the track and may be integrated into the track or suspended in a pendant mount. In addition, some individual track lights can be connected directly to a junction box. Ballasts are typically housed in the track head, although ballasts may also be recessed into the ceiling plenum. Track lights also offer options for switching individual lamps or groups of lamps.
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Figure 1: HID track lighting fixture Track lights for HID lamps are similar to those for incandescents, but they typically house the ballasts for the lamp in the track head. Source: E Source |
Accessories available for track lights include lenses that alter the beam shape, louvers and tubular shields that cut down on glare and filters that change the colour of the light. Some products also offer a ballast fuse that prevents damage from voltage surges.
How to make the best choice
Compare the cost-effectiveness of HID and incandescent alternatives. The cost-effectiveness of HID track lights depends on the intensity of their use and local electricity costs. HID lamps' energy efficiency and long life make up for higher first costs most quickly in areas where electricity costs are highest, and in applications where maintenance costs are high and usage is most intense. Use the online calculator below as a screening tool to compare the costs of halogen, MH and HPS alternatives for a given application.
HID Track Lighting Savings Calculator
Try before you buy. HID lamps produce different colour effects than incandescents, so test the lighting before any major conversion to be sure that the results are acceptable. In addition, because ballasted fixtures (unlike incandescent fixtures) are designed to work with only one lamp wattage, it is important to specify the right lamp size to begin with. If a 70-watt lamp turns out to provide too much light, substituting a lower-wattage HID lamp will only produce more rapid lamp burnout because the ballast will continue to send 70 W into the new lamp.
Account for lumen depreciation when specifying an HID system. HID lamps lose 10% to 40% of their rated output after 40% of their rated life; halogen lamps lose less than 5%. This phenomenon can shorten the lamp's effective life if output becomes too dim for the application or it can force designers to overlight the application to begin with.
If ultraviolet (UV) radiation could cause problems, take steps to minimize UV output. The high levels of UV put out by MH lamps can damage sensitive fabrics, papers and artifacts. Special filtering can help prevent damage: some metal MH track lights are available with special attachments to hold the filters. HPS lamps, which produce little UV radiation, are also an option.
Use HID lamps where heat is a problem. HID lamps emit much less infrared radiation than incandescents do, which keeps the illuminated subject cooler. This feature can reduce fading and drying of objects and may increase the lifetimes of some displayed objects, such as food.
Do not use HID lamps where warm-up and restrike delays could cause problems. HID lamps require a warm-up period, which can be troublesome after power interruptions or in applications where lights are frequently turned on and off. The problem is worse for MH lamps, for which start-up takes three to five minutes and restrike (after a shutdown or power interruption) takes 10 to 20 minutes. Start-up for an HPS lamp takes three to four minutes, but restrike takes less than a minute.
Do not use HID track lights if tight beam spreads are required. HID lamps are available in both flood and spot-lamp configurations, but use halogen reflector lamps, such as the MR 16, for tight-beam spreads of less than seven degrees.
What's on the horizon?
Dimming has been difficult to accomplish with HID lamps and has mostly been available on 150 watts and larger lamps. When HID lamps are dimmed, light output decreases far more than power input so lamp efficacy decreases. Lamp life may also decrease and the rate of lumen depreciation increases, if lamps are operated at low light levels for prolonged periods. Most dimming systems to date have been two-step systems that provide 100% and 50% of output. However, new electronic ballasts are being developed that solve some of the dimming challenges. In the next few years, look for better continuous-dimming systems that dim down to 30%.
New light-emitting diode (LED) technology, which can be applied to track lighting, is under development. The technology uses microprocessors to combine red, green and blue LEDs to produce a wide array of colours. LED lamps are more efficient than those that use filtered incandescent light and they are safer for illuminating sensitive items, such as fabrics and paintings in art galleries.
Copyright © 2006 E Source Companies LLC
Last Modified: May 9, 2009
