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Energy-Efficiency Glossary: Lighting

Accent Lighting — Indoor and outdoor illumination that draws attention to special features or enhances aesthetic qualities.

Ambient Lighting — General, everyday indoor illumination and outdoor illumination for safety and security purposes. For illumination required to preform specific tasks, see Task Lighting.

Color Temperature — The color produced by a light bulb. Bulbs that produce yellow-red colors, like incandescent bulbs, are considered to be warm, while blue-green colors are considered cool. Cool light is typically preferred for performing visual tasks since it produces higher contrasts. Warm light is usually preferred for living spaces since its lower contrast is more flattering to skin tones and clothing. Color temperature is measured in degrees Kelvin (K), with cool colors producing higher temperatures (3600–5500 K) and warm colors producing lower temperatures (2700–3000 K). Color temperatures between 2700–3600 K are usually recommended for most indoor and task lighting.

Color Rendition — How colors appear when illuminated by a light bulb. The Color Rendition Index (CRI) is a 1–100 scale that measures a light bulb’s ability to make colors appear naturally, the same way that sunlight does. Color rendition is generally considered more important than color temperature. A CRI of 100 is based on the illumination of a 100-watt incandescent light bulb. A bulb with a CRI of 80 or greater is considered adequate for using indoors at home.

Efficacy — The ratio of light produced (lumens) to energy consumed (watts); a general measurement of the energy efficiency of a light bulb. Efficacy is determined by dividing the number of lumens a bulb produces by the amount of electricity used to operate the bulb (lumens per watt).

Footcandle — The intensity of light emitted by a light bulb. A footcandle describes the intensity of illumination produced by one lumen over a 1-square-foot area. For most home and office lighting, 30–50 footcandles of illumination is adequate. For more detailed work requiring more accuracy and less eyestrain, 200 footcandles of illumination or greater is ideal. For nightlights, 5–20 footcandles may be sufficient.

Glare — The excessive brightness from a direct light source that can make it difficult to see clearly; for example, sunlight shining on a TV or an incandescent light bulb shining on a computer monitor. Incandescent light bulbs generally produce more glare than other kinds of bulbs, but glare is primarily the result of where lighting is placed relative to where objects are being viewed.

Illumination — The distribution of light on a horizontal surface; the basic purpose of all lighting. Not to be confused with the intensity or brightness of light (see Footcandle, Lumen).

Lumen — The brightness of light emitted by a light bulb. For example, a 100-watt incandescent light bulb emits about 1600 lumens, while a 60-watt incandescent light bulb emits about 800 lumens. Not to be confused with the amount of electricity used to power a light bulb (see Watt). An energy-efficient compact fluorescent light bulb will use fewer watts to produce comparable lumens. For example, an energy-efficient 13- watt light bulb that emits 870 lumens might use only 13 watts of electricity, roughly the equivalent of a 60-watt incandescent light bulb(see Efficacy).

Task Lighting — Illumination provided for specific tasks that require more illumination than ambient lighting can provide, such as computer desk lamps and bathroom mirror lights.

Watt — A measurement of the amount of electricity used to power a light bulb. Not to be confused with the brightness of a light bulb (see Lumen). Shoppers often make the mistake of purchasing light blubs based on wattage rather than lumens. However, an energy-efficient light bulb typically uses far fewer watts to produce the same lumens as an incandescent bulb. Consumers should instead compare the lumens of light bulbs when shopping for replacement bulbs. The energy efficiency of a light bulb is measured by its ratio of lumens to watts (see Efficacy).

Sources

U.S. Department of Energy, Energy Efficiency & Renewable Energy, “Lighting Principals and Terms

U.S. Department of Energy, Energy Efficiency & Renewable Energy, “Lumens and the Lighting Facts Label

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