High-intensity discharge (HID) lighting provides the second highest efficacy and longest service life of any lighting type. Both HIDs and LEDs can save 75%–90% of lighting energy when they replace incandescent lighting. In a high-intensity discharge lamp, electricity arcs between two electrodes, creating an intensely bright light. Mercury, sodium, or metal halide gas acts as the conductor.
|In a high-intensity discharge lamp, electricity arcs
between two electrodes, creating an intensely
bright light. Mercury, sodium, or metal halide gas
act as the conductor.
HID lamps use an electric arc to produce intense light. Like fluorescent lamps, they require ballasts. They also take up to 10 minutes to produce light when first turned on because the ballast needs time to establish the electric arc. Because of the intense light they produce at a high efficacy, HID lamps are commonly used for outdoor lighting and in large indoor arenas. Because the lamps take awhile to establish, they are most suitable for applications in which they stay on for hours at a time.
HID ballast technology is very old and often highly inefficient. Interfacing HID with advanced controls is difficult and dimming is not practical. LEDs are rapidly displacing many traditional HID lighting markets, such as stadium and roadway lighting, because they turn on instantly and are easily dimmed and controlled.
The three most common types of high-intensity discharge lamps are:
Mercury Vapor Lamps
Mercury vapor lamps—the oldest types of high-intensity discharge lighting—were formerly used for street lighting, but are now only rarely used for that purpose. Nearly all new lamps sold in North America today for street lighting are either metal halide or LEDs, which have also displaced mercury vapor lamps in sports arenas and gymnasiums. Mercury vapor lamps provide about 50 lumens per watt, but ballast loss can reduce the system efficacy to about 30 lumens per watt, which is not competitive with LEDs.
Metal Halide Lamps
Metal halide lamps produce a bright, white light with the best color rendition among high-intensity lighting types. They are used to light large indoor areas, such as gymnasiums and sports arenas, and outdoor areas, such as car lots.
Metal halide lamps are similar in construction and appearance to mercury vapor lamps. The addition of metal halide gases to mercury gas within the lamp results in higher light output, more lumens per watt, and better color rendition than from mercury gas alone.
High-Pressure Sodium Lamps
High-pressure sodium (HPS) lighting—a type of high-intensity discharge lighting—are rarely used in North America. Other, more efficacious and higher quality lamp types have displaced HPS lamps from nearly all of their traditional markets. The only remaining significant application of HSP lamps is in parking garages, but LEDs are also displacing them from that application.