Outdoor Lighting Glossary

Come across a lighting word you aren't sure of? Completely new to the world of lighting? We feel your pain! Here you will find a collection of terms and concepts that should help to make your life easier.

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Select the first letter of the word from the list above to jump to appropriate section of the glossary.

Candela (cd) - The unit of measurement of luminous intensity of a light source in a given direction

Candlepower - Luminous intensity expressed in candelas.

Candlepower Distribution Curve - A graphic presentation of the distribution of light intensity in a given plane of a lamp or luminaire. It is determined by photometric tests. The curve is generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.

Ceiling Cavity Ratio - A numerical relationship of the vertical distance between luminaire mounting height and ceiling height to room width and length. It is used with the Zonal Cavity method of calculating average illumination levels.

Chromaticity - Refers to the dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together.

Circuit Breaker - Resettable safety device to prevent excess current flow.

Class "P" Ballast - Contains a thermal protective device which deactivates the ballast when the case reaches a certain critical temperature. The device resets automatically when the case temperature drops to a lower temperature

Coefficient of Utilization (CU) - A ratio representing the portion of light emitted by a luminaire in any particular installation that actually gets down to the work plane. The coefficient of utilization thus indicates the combined efficiency of the luminaire, room proportions and room finish reflectances. The ratio of the luminous flux (lumens) from a luminaire is calculated as received on the work-plane to the luminous flux emitted by the luminaire's lamps alone

Cold Cathode Lamp - An electric-discharge lamp whose mode of operation is that of a glow discharge

Color Corrected - Refers to a lamp with a special phosphor or coating (applied internally or externally) to give it a color rendering profile more like that of natural daylight.

Color Rendering Index (CRI) - Measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature; a quality of the light. It is a measure of the lamp's ability to `'render" colors accurately.

Color Spectrum - Same as the "visible light" spectrum: electromagnetic energy between 380 (violet) and 770 (red) nanometers, which can be seen by the human eye.

Color Temperature - The absolute temperature of a blackbody having a chromaticity equal to that of the light source. Expressed in degrees Kelvin, color temperature indicates the color of a light source.

Compact Fluorescent - A small fluorescent lamp that is often used as an alternative to incandescent lighting. The lamp life is about 1O times longer than incandescent lamps and is 3-4 times more efficacious. Also referred to as PLI DL, CFL or BIAX lamps.

Cone - In the eye, a retinal receptor that dominates the retinal response when the luminance level is high and provides the basis for the perception of color.

Cone Reflector - Parabolic reflector that directs light downward thereby eliminating brightness at high angles

Contrast - The difference in brightness (luminance) of an object and its background.

Contrast Rendition Factor (CRF) - The ratio of visual task contrast with a given lighting environment to the contrast with sphere illumination. Contrast measured under sphere illumination is defined as 1.00.

Cool Beam Lamps - Incandescent PAR lamps that use a special coating (dichronic interference filter) on the reflectorized portion of the bulb to allow heat to pass out the back while reflecting only visible energy to the task, thereby providing a "cool beam" of light.

Correlated Color Temperature (CCT) - the "color" of the light given off by a lamp.

Cosine Law - The law that the illuminance on any surface varies as the cosine of the angle of incidence. (The angle of incidence is the angle between the normal to the surface and the direction of the incident light.)

Cove Lighting - Refers to light sources mounted above a ledge or in a recess (usually around the perimeter of a room) that distribute light upward for ambient lighting.

Cutoff Angle (of a luminaire) - The angle from the vertical at which a reflector, louver, or other shielding device cuts off direct visibility of a light source. It is the complementary angle of the shielding angle. In the case of reflector-type lightshields it is also important to ascertain the cutoff angle to the reflected image of the light source as this is often almost as bright as the source itself.

Cutoff Luminaires - Outdoor luminaires that restrict all light output to below 85° from vertical.