HID light bulbs are electrical gas-discharge lamps that uses an electric arc that occurs between tungsten electrodes to produce light. These electrodes are housed inside a transparent or translucent fused alumina or fused quartz arc tube that has been filled with gas and metal salts. High intensity discharge (HID) lamps come in various types such as mercury vapor, high and low pressure sodium and metal halide. HID lamps have greater energy efficiency than fluorescent and incandescent lamps, emitting more lumens per watt. High intensity discharge lamps have many uses, particularly where very bright light is required. This includes outdoor lighting, studio and stage lighting, medical lighting, lights for transportation and commercial lighting. HID lights can also be used in downlighting fixtures and as indoor spotlights.