High-Intensity Discharge (HID) Lighting

Lighting in older facilities typically employs some sort of high-intensity discharge system, particularly in high-bay applications where greater lumen output is needed. The HID family includes mercury vapor, metal halide, and high-pressure sodium lamps.

Mercury vapor lamps, the first to be invented, are not often used because of their poor color rendering and inefficiency. Metal halide have a much better efficacy, meaning the ratio of lumens to watts, and can achieve very accurate color rendering, as measured by the color rendering index (CRI). High-pressure sodium (HPS) lamps have an even higher efficacy, but cast a golden light that distorts colors. For this reason, HPS are often used in outdoors applications. Low-pressure sodium (LPS) lamps, which are not actually HIDs but are often compared with them, have the highest efficacy rating, but the lowest CRI rating, and are used almost exclusively outdoors.

In most cases, HIDs can be cost-effectively replaced with high-output T8 and T5HO fluorescents, even in high-bay applications.