High Intensity Discharge (HIDs)
HIDs produces light when an arc passes between cathodes in a pressurized tube, causing metallic additives to vaporize. They are similar to fluorescents in that an arc is generated between two electrodes. Some types of HIDs are high-pressure sodium lamp(HPS), low-pressure sodium lamp(LPS), metal halide, and mercury vapor. Except for metal halides, this light bulb does not produce any colours. Most parking lots, shopping centers and sports arenas now use HIDs or LPS lamps, since they are especially useful for outdoor security lighting and area lighting. They can also be considered for indoor use, particularly rooms with very high ceilings. Some advantages to it is that they have long lives, relatively high lumen output per watt, and small in size. The sodium lamps are among the most efficient lamps in the world, and they are powerful within large areas, and the lumen output doesn’t drop with age, unlike some other light bulbs. There are some disadvantages too. HIDs require time to warm up, which is inconvenient, and sometimes they would have a momentary interruption of current or a voltage drop too low to maintain, and the arc will extinguish the lamp. LPS have bad colour rendering too.