Rods dominate at low luminance levels, but give no significant color perception.Ĭonspicuity: The capacity of a signal to stand out in relation to its background so as to be readily discovered by the eye (as in lettering on a sign, for example).Ĭorrelated Color Temperature (CCT): A measure in degrees Kelvin (°K) of light’s warmness or coolness. Cones dominate the response when the luminance level is high, and provide color perception. Specify both the CCT and CRI when purchasing lamps.Ĭones and rods: Groups of light-sensitive cells in the retinas of animal eyes. It is important not to mix lamps with different CCTs and CRIs. A high CRI provides better illumination with the same or lower lighting levels. Sets most lighting standards.Ĭoefficient of Utilization (CU): Ratio of luminous flux (lumens) from a luminaire received on the “work plane” to the lumens emitted by the luminaire.Ĭolor rendering: Effect of a light source on the color appearance of objects in comparison with their color appearance under normal daylighting.Ĭolor Rendering Index (CRI) A measure of the accuracy with which a light source of a particular CCT renders different colors in comparison to a reference light source with the same CCT. Formerly called the candle.Ĭandlepower distribution curve: A plot of the variation in luminous intensity of a lamp or luminaire.Ĭandlepower: Luminous intensity expressed in candelas.ĬIE: Commission Internationale de l’Eclairage. Lamp often is used to denote the bulb and its housing.Ĭandela (cd): Unit of luminous intensity.
To be distinguished from the whole assembly (see luminaire). Note that some of these definitions are quite subjective, and are offered here as guidance only.Īccent lighting: Lighting used to emphasize or draw attention to a special object or building.Īdaptive Controls: Devices such as motion sensors, timers and dimmers used in concert with outdoor lighting equipment to vary the intensity or duration of operation of lighting.Īmbient light: The general overall level of lighting in an area.Īngstrom: A unit of wavelength often used in astronomy, equal to 10 -10 meter or 0.1 nanometer.īaffle: An opaque or translucent element to shield a light source from direct view.īallast: A device used with a discharge lamp to obtain the necessary voltage, current, and/or wave form for starting and operating the lamp.īeam spread: The angle between the two directions in the plane in which the intensity is equal to a given percentage (usually 10 percent) of the maximum beam intensity.īrightness: Strength of the sensation that results from viewing surfaces from which the light comes to the eye.īulb or lamp: The source of electric light. For further information and formal definitions please see discussions in standard dictionaries, encyclopedias, the IES Lighting Handbook, and other lighting industry books. We include in this glossary definitions for a number of the basic terms and words used in the lighting community.
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