(pronounced like the initials: aych-eye-dee)
HID stands for “high-intensity discharge”, as in the type of lighting where gas – usually metal halide, high-pressure sodium or mercury – acts as the conductor of electricity between two electrodes within a lamp, creating an intensely bright light. This powerful light also happens to be incredibly energy efficient. Not only can HID lamps save 75%–90% of the energy over incandescent ones, but they also have the longest service life of any lighting type, save LED. Like fluorescent varieties, HID lamps require ballasts. As ballasts require a little time to establish the electric arc, it can take up to ten minutes for the lamp to reach peak output, making the pairing of motion detectors ineffective. Therefore, HIDs are most commonly used in situation where they will remain on for many hours – e.g., parking lots and garages and other exterior lighting applications, big box retail stores, indoor arenas, etc. Depending on the type of vapor used, color rendering can be less than attractive. More recently, technological advancements in HID xenon gas lamps have allowed them to be used for fog lamps and car headlights because they produce very clear, white light but consume less energy than traditional halogen lamps.