High-Intensity Discharge Lamps
High Pressure Sodium (HPS), Metal Halide, Mercury Vapor and Self-Ballasted Mercury Lamps are all high intensity discharge lamps (HID). Auxiliary equipment such as ballasts and starters must be provided for proper starting and operation of each type bulb, with the exception of self-ballasted lamps. HID lamps produce a large quantity of light from a relatively small bulb, compared to fluorescent and incandescent lamps.
Housed inside a specially designed inner glass tube, HID lamps produce light by striking an electrical arc across tungsten electrodes. This tube is filled with both gas and metals. The gas aids in the starting of the lamps. Then, once they are heated to a point of evaporation, the metals produce the light.
Metal Halide Bulb
Though they produce a yellowish light, standard high-pressure sodium lamps have the highest efficiency of all HID lamps. Efficiency is somewhat sacrificed, however, High-pressure sodium lamps that produce a whiter light are now available. Metal halide lamps are less efficient but produce a whiter, more natural light. Colored metal halide lamps are also available. HID lamps are usually used not only when energy efficiency and/or long life are desired, but also when high levels of light are required over large areas. Such areas include gymnasiums, pathways, outdoor activity areas, roadways, large public areas, and parking lots. Recently, metal halide is successfully being used in residential environments.
Low-Pressure Sodium Lamps
Of all commercially available lighting sources, Low-pressure sodium lamps have the highest efficiency. A low-pressure sodium lamp shouldn't be confused with a standard high-pressure sodium lamp, even though they both emit a yellow light. Requiring a ballast, Low-pressure sodium lamps operate much like a fluorescent lamp. There is a brief warm-up period for the lamp to reach full brightness.
Low-pressure sodium lamps are generally used where color rendition is not important but energy efficiency is. They are typically used for outdoor, roadway, parking lot, and pathway lighting.
LED or Light Emitting Diodes
Light Emitting Diodes (LED) are bulbs without a filament, that are low in power consumption and have a long life span. LEDs are just starting to rival conventional lighting, but unfortunately they just don't have the output (lumen) needed to completely replace incandescent, and other type, bulbs just yet. Never the less, technology is advancing everyday, and it will not be long until the LED bulb will be the bulb of choice for most applications in the home and work place.
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