What are they?

HID, orhigh-intensity discharge light bulbs and lamps, are a family of gas-dischargearc lamps which create light by sending an electrical discharge between twoelectrodes and through a plasma, or ionized gas. An additional gas is generallyused, and this gas serves as an easy way to classify the major types of HIDlamps: Mercury, sodium, and metal halide.

Theselamps are known for their high efficiency at turning electricity into light andtheir long rated life. HID lamps require a ballast in order to generate theinitial surge of electricity needed to start them and to regulate their powerduring normal operation.