HID

From CPFWiki

High Intensity Discharge (HID)lamps have no filament, contain gas and Halide salts. They are very much more efficient than tungsten filament lamps. They also require a vey high voltage pulse to ignite the arc inside which must be operated by a regulated ballast. They take many seconds of operation to come up to full brightness. They are NOT(!!) similar to xenon short-arc bulbs which do not have halide salts, have much higher surface brightness, are less efficient and start instantly. D2S and D2R HID bulbs are used in car headlights as well as X990 and other super lights. Xenon short-arc discharge bulbs are widely used in motion picture projectors, spotlights, and portable search lights (Maxabeam, Spectrolab). They contain Xenon gas and tungsten electrodes. All of these types of discharge bulbs and ballasts tend to be more expensive than LED and tungsten bulbs. They run at high temperatures and pressures and can be very, very dangerous if not properly enclosed and protected from water while operating. They also have UV in their output so can damage vision if care is not taken to avoid direct exposure.

Simple Carbon discharge lamps have been around far longer than Tom Edison's light bulb. They were very harsh (a lot of UV, not well understood in 1800's) and Edison wanted a softer light for common indoor lighting. Also longer running than carbon arc which required HOURLY maintenance.

Modern HID bulbs run for thousands of hours without maintenance. Mostly in street lights. Modern Xenon Arc lamps are used in theater projectors and other industrial applications.