High-Intensity Discharge: High-intensity discharge (HID) lamps provide the highest efficacy and longest service life of any lighting type. They are commonly used for outdoor lighting and in large indoor arenas.

HID lamps use an electric arc to produce intense light. They also require ballasts, and they take a few seconds to produce light when first turned on because the ballast needs time to establish the electric arc.

The three most common types of HID lamps are mercury vapor, metal halide, and high-pressure sodium. HID lamps and fixtures can save 75% to 90% of lighting energy when they replace incandescent lamps and fixtures. Significant energy savings are also possible by replacing old mercury vapor lamps with newer metal halide or high-pressure sodium lamps.

Mercury vapor-the oldest type of HID lighting-is 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 Most indoor mercury vapor lighting in arenas and gymnasiums has been replaced by metal halide lighting, which has better color rendering and efficiency.

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 are used to light large indoor areas such as gymnasiums and sports arenas, and for outdoor areas such as car lots or anywhere that color rendition is important.

High-pressure sodium lighting is becoming the most common type of outdoor lighting. It provides 90 to 150 lumens per watt-an efficiency exceeded only by low-pressure sodium lighting. High-pressure sodium lamps are also reliable and have long service lives. Their color is a warm white, and their color rendition ranges from poor to fairly good depending on design and intended use.

Low-Pressure Sodium: Low-pressure sodium lamps work somewhat like fluorescent lamps. They are the most efficient artificial lighting, have the longest service life, and maintain their light output better than any other lamp type. Low-pressure sodium lighting is used where color is not important because it renders all colors as tones of yellow or gray. Typical applications include highway and security lighting.

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Figure 109: Lights listed in order as seen above: Incandescent, Mercury, Fluorescent, Metal Halide, High-pressure Sodium, and Low-pressure Sodium


Energy Efficiency with Lighting: Lighting accounts for 20% to 25% of all electricity consumed in the United States. An average household dedicates 5% to 10% of its energy budget to lighting, while commercial establishments consume 20% to 30% of their total energy just for lighting.

In a typical residential or commercial lighting installation, 50% or more of the energy is wasted by obsolete equipment, inadequate maintenance, or inefficient use.

Saving lighting energy requires either reducing electricity consumed by the light source or reducing the length of time the light source is on. This can be accomplished by:

  • Lowering wattage, which involves replacing lamps or entire fixtures

  • Reducing the light source's on-time, which means improving lighting controls and educating users to turn off unneeded lights

  • Using daylighting, which reduces energy consumption by replacing electric lights with natural light

  • Performing simple maintenance, which preserves illumination and light quality and allows lower initial illumination levels.

Replacing Lamps and Fixtures: "Relamping" means substituting one lamp for another to save energy. You can decide to make illumination higher or lower when relamping. But be sure that the new lamp's lumen output fits the tasks performed in the space and conforms to the fixture's specifications. When relamping an entire store or office, first test the new lamps in a small area to ensure adequate illumination, occupant satisfaction, and compatibility of the new lamp and the old fixture.

Matching replacement lamps to existing fixtures and ballasts can be tricky, especially with older fixtures. Buying new fixtures made for new lamps produces superior energy savings, reliability, and longevity compared with relamping.

Relamping incandescent fixtures: Much has been learned about fixture design since the energy crises of the 1970s. Many indoor fixtures trap a significant portion of light inside the fixture, while many outdoor fixtures tend to disperse much of their light beyond the intended area, which causes light pollution.  New incandescent fixtures are designed to push all their light out into the room. Others use smaller tungsten halogen lamps. Advances in indoor fixture design include brighter reflectors and better reflecting geometry.

Many incandescent lamps are mismatched to their tasks. Some have excessive wattages and therefore create unnecessarily high illumination. This can be corrected by using lamps with smaller wattage. Some existing incandescent lamps may not be the best type of lamp for their application. A-type light bulbs can often be replaced with improved lamp designs, such as reflectors or tungsten halogen lamps. And, for energy savings of 60% to 75%, many incandescent lamps can be replaced by CFLs.

When used in recessed fixtures, standard A-type lamps and reflector lamps waste energy because their light gets trapped. To save energy, you could replace a 150-watt standard reflector with a 75-watt ellipsoidal reflector (ER). Remember, though, that ER lamps are less efficient at delivering light from shallow fixtures, so use reflectors or parabolic reflectors for these purposes.

You can also replace standard A-type lamps with CFLs in spaces where lights are needed for long periods of time. A standard 18-watt CFL replaces a 75-watt A-type lamp. CFLs are also packaged in the same glass reflector lamps as incandescent lamps. Use CFLs packaged as ellipsoidal reflectors (type-ER) in recessed fixtures. Use reflector (R) or parabolic reflector (PAR) CFLs for flood and spotlighting. New CFL fixtures have built-in electronic ballasts and polished metal reflectors.

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