What is HID?
The term HID is used in lamps and the acronym stands for High Intensity Discharge lamp. HID lamp is a kind of lamp that produces high intensity light but in reduced power consumption. HID lamp is actually a type of arc lamp. To produce the high intensity light, an arc tube houses tungsten electrodes. Between the tungsten electrodes is an electric arc. The arc tube is filled with gas and metal salts in which when the arc heats after starting. Once the electric arc heats up, the metal salts evaporate and forms plasma. The plasma makes the light so intense that it appears brighter than ordinary lamps.
When it comes to luminous efficacy, HID lamps have higher rating compared to ordinary incandescent and fluorescent lamps. Luminous efficacy pertains to the output of light per watt of electricity input. The reason why HID lamps have more intense light is for having a greater proportion of visible light as to heat.
Chemistry plays an important role in the construction of HID lamps. There are different types of chemicals used in the construction of HID lamps. The chemical used depends on how much intensity of light is desired. The desired characteristics of the light are CRI or Color Rendering Index, correlated color temperature, lifespan and energy efficiency.
There are different HID lamps in terms of chemical used. There are 6 popular HID lamps commercially available. They are Mercury vapor lamps, Metal Halide or MH lamps, Ceramic Metal Halide lamps, Sodium vapor lamps, UHP of Ultra-High Performance lamps and Xenon short-arc lamps.
The first commercially available HID lamp is the Mercury vapor lamps. This type of HID lamp produces a light that is bluish green. However, the newer versions have lesser color tint. Mercury vapor lamps produce bright lights although people favor the use of metal halide and sodium vapor lamps as of present.
Metal halide or MH lamps are getting more popular over mercury vapor lamps due to neutral white light it gives off. The same goes for ceramic metal halide, in which both type of lamps are used widely on movie production, automotive headlamps, sports games held during night time (indoor or outdoor) and lighting for aquariums.
For photography use, low-pressure sodium vapor lamps are more favorable. These types of lamps are considered extremely efficient as they give off deep yellow orange light. CRI rating is almost zero that subjects viewed under these lamps appear monochromatic. The light given off by this type of lamp is considered to be photographic safe.
HID lamps are used in various applications. Such types of lamps are typically used in areas where high levels of lights are needed. Large venues or areas such as arenas, football stadiums, large gymnasiums, warehouses, roadways parking lots and etc. are some of the examples that require the use of HID lamps.
Although HID lamps are specifically useful in many applications, such lamps produce ultraviolet rays, which are considered harmful. To prevent people from being exposed to UV radiation given off by HID lamps, UV blocking filters are included in the construction of these lamps.