High Intensity Discharge Lamps - Mainly Commercial Use

High intensity discharge (HID) lamps provide the highest efficacy (greatest amount of light or lumens per watt)and are longer lasting than any other lighting.

Replacing incandescent lamps with HIDs can save 75%–90% of lighting energy. Because of the intense light they produce at a high efficacy, HID lamps are commonly used for outdoor lighting and in large indoor arenas. Since the lamps take awhile to reach brightness, they are most suitable for applications where they stay on for hours at a time.

How They Work
High intensity discharge lamps use an electric arc between tungsten electrodes housed inside a translucent or transparent tube to produce intense light. This tube is filled with both gas and metal salts.

The gas facilitates the arc's initial strike which then heats and evaporates the metal salts forming a gas cloud or plasma. This plasma greatly increases the intensity of light produced by the arc and reduces its power consumption.

Like fluorescent lamps, they need ballasts. They also take up to ten minutes to produce light when first turned on, because the ballast needs time to establish the electric arc. They are best in areas where lights need to stay on for long periods of time. They are not suitable for use with motion detectors.

Types of High Intensity Discharge Lamps
Varieties of HID lamp include:

• Mercury vapor lamps - The oldest type of high-intensity discharge lighting and used mainly for street lighting. The new styles are much more energy efficient and give off about 50 lumens/watt
• Metal halide (MH) lamps - Used to light large indoor areas, such as gymnasiums and sports arenas, and outdoor areas, such as car parking lots. Metal halide lamps have shorter lifetimes (5,000–20,000 hours) compared to both mercury vapor and high-pressure sodium lamps.
• Sodium vapor lamps - The most common type of outdoor lighting today. High-pressure sodium lamps have an efficacy of 50–140 lumens per watt—an efficiency exceeded only by low-pressure sodium lamps.

  They produce a warm white light. Like mercury vapor lamps, high-pressure sodium lamps have poorer color rendition (how the object looks under the light as compared to under sunlight)than metal halide lamps but longer lifetimes (16,000–24,000 hours).

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