High Intensity Discharge (HID) lighting is the technology where light is created from electrical current passing through metal vapor. In HID bulbs, a tube of glass is filled with gas and has two electrodes on either side. When an arc of electrical current is established between the electrodes, the metallic vapor releases energy in the form of light. HID lightinghas several advantages over fluorescent or halogen lighting and is starting to be used more as a replacement for halogen lights as automobile headlights.