High Intensity Discharge (HID) Lighting
How does it Work?
HID (high intensity discharge) lamps are used when high levels of light are needed to cover large areas such as warehouses, ball parks, theme parks, airport hangers and similar. HID is a type of electrical gas-discharge lamp, which produces light by means of an electric arc between tungsten electrodes. These are housed inside a translucent or transparent fused quartz or fused alumina arc tube. The tube is filled with both gas and metal salts. The gas facilitates the arc’s initial strike. Once the arc is started, it heats and evaporates the metal salts forming a plasma. The plasma increases the intensity of light produced by the arc and reduces its power consumption.
HID lamps make more visible light per unit of electric power consumed than fluorescent and incandescent lamps since the greater proportion of their radiation is visible light in contrast to infrared. The high demand for HID lighting comes from the efficiency of the lamp and the ability to light vast areas.
There are various types of chemistry used in the arc tubes of HID lamps depending on the desired characteristics of light intensity, correlated color temperature, color rendering index (CRI), energy efficiency and lifespan. These include:
The light-producing element of these lamp types is a well-stabilized arc discharge contained within a refractory envelope arc tube with a wall loading in excess of 3 W/cm2 (19.4 W/in2).
Mercury vapor lamps were the first commercially available HID lamps. They originally produced a bluish-green light, but more recent versions can produce light with less pronounced color tint. This said, mercury vapor lamps are not as favorable today and are now being replaced by sodium vapor and metal halide lamps.
Metal halide and ceramic metal halide lamps can be made to give off neutral white light, which is useful for applications where normal color appearance is important such as watching TV, evening indoor sports games and aquarium lighting.
Low-pressure sodium vapor lamps are very efficient. The lamp produces a deep yellowish-orange light and with a color-rendering index of almost zero. Although the color has been corrected with newer versions some efficiency is given up for a better color.