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    Question ID:   6046         Current Version: 1
Question: What is high-intensity discharge lighting?
Category: Home Maintenance & Repairs > Electrical & Lighting
Keywords: high, pressure, intensity, discharge, lighting, mercury, vapor, metal, halide, sodium, lamp, HID
Type: what
Rating:(0 ratings)    Views: 203    Discussions: 0   In Watch Lists: 1  

 
    Answer:

High-intensity discharge (HID) lamps provide the highest efficacy and longest service life of any lighting type. They can save 75%-90% of lighting energy when they replace incandescent lamps.

HID lamps use an electric arc to produce intense light. Like fluorescent lamps, they require 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.

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 establish, they are most suitable for applications where they stay on for hours at a time. They are not suitable for use with motion detectors.

In a high-intensity discharge lamp, electricity arcs between two electrodes, creating an intensely bright light. Mercury, sodium, or metal halide gases act as the conductor. 

Types of High-Intensity Discharge Lamps

These are the three most common types of HID lamps:

  • Mercury vapor lamps

Mercury vapor lamps-the oldest types of high-intensity discharge lighting-are used primarily for street lighting.

Mercury vapor lamps provide about 50 lumens per watt. They cast a very cool blue/green white light. Most indoor mercury vapor lamps in arenas and gymnasiums have been replaced by metal halide lamps. Metal halide lamps have better color rendering> and a higher efficacy. However, like high-pressure sodium lamps, mercury vapor lamps have longer lifetimes (16,000-24,000 hours) than metal halide lamps.

Significant energy savings are also possible by replacing old mercury vapor lamps with newer high-pressure sodium lamps.

  • Metal halide lamps

Metal halide lamps produce a bright, white light with the best color rendition among high-intensity lighting types. They are used to light large indoor areas, such as gymnasiums and sports arenas, and outdoor areas, such as car lots.

Metal halide lamps are similar in construction and appearance to mercury vapor lamps. The addition of metal halide gases to mercury gas within the lamp results in higher light output, more lumens per watt, and better color rendition than from mercury gas alone.

Metal halide lamps have shorter lifetimes (5,000-20,000 hours) compared to both mercury vapor and high-pressure sodium lamps.

  • High-pressure sodium lamps

High-pressure sodium lighting-a type of high-intensity discharge lighting-is becoming the most common type of outdoor lighting.

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 than metal halide lamps but longer lifetimes (16,000-24,000 hours).

You can use the chart below to compare these types of lamps. If you don't already, it helps to understand basic lighting principles and terms before making comparisons.

High-Intensity Discharge Lighting Type Efficacy
(lumens/watt)
Lifetime
(hours)
Color Rendition Index
(CRI)
Color Temperature
(K)
Indoors / Outdoors
Mercury vapor 25–60 16,000–24,000 50 (poor to fair) 3200–7000 (warm to cold) Outdoors
Metal halide 70–115 5000–20,000 70 (fair) 3700 (cold) Indoors/outdoors
High-pressure sodium 50–140 16,000–24,000 25 (poor) 2100 (warm) Outdoors

Source: Energy Efficiency and Renewable Energy, U.S. Department of Energy

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