22 August 2006
Candlepower (cp), I = dφ/dω - luminous intensity expressed in candelas.
Clerestory that part of a building that rises clear of the roofs or other parts and whose
walls contain windows for lighting the interior.
Coefficient of Utilization (CU) the ratio
of luminous flux (lumens) calculated
received on the work plane to the total luminous flux (lumens) emitted by the lamps
alone. It is equal to the product of room utilization factor and luminaire efficiency.
Color Matching the action
a color appear the same
as a given color.
a general expression for the effect
of a light source
on the color
appearance of objects in conscious or subconscious comparison with their color
appearance under a reference light source.
Color Rendering Index (of a light source) (CRI) a measure of the degree of color
shift objects undergo when illuminated by the light source as compared with those same
objects when illuminated by a reference source of comparable color temperature.
Color Temperature (of a light source) the absolute temperature of a blackbody
radiator having a chromaticity equal to that of the light source. Refer to Correlated Color
Contrast see luminance contrast.
Correlated Color Temperature (of a light source) (CCT) the absolute temperature
of a blackbody whose chromaticity most nearly resembles that of the light source.
Daylight Availability the luminous flux from the
sun plus sky
at a specific location,
time, date, and sky condition.
Diffused Lighting lighting provided on the work plane or on an object that is not
incident predominantly from any particular direction.
Dimmer a device used to control the intensity of light emitted by a luminaire by
controlling the voltage or current available to it.
Direct Component that portion of the light from a luminaire that arrives at the work
plane without being reflected by room surfaces.
Direct Glare glare resulting from high luminances or insufficiently shielded light
sources in the field of view. It is usually associated with bright areas, such as
luminaires, ceilings, and windows that are outside the visual task or region being
viewed. A direct glare source can also affect performance by distracting attention.
Direct-Indirect Lighting a variant of general diffuse lighting in which the luminaires
emit little or no light at angles near the horizontal.
Direct Lighting lighting involves luminaires that distribute 90 to 100% of the emitted
light in the general direction of the surface to be illuminated. The term usually refers to
light emitted in a downward direction.
Directional Lighting lighting provided on the workplane or on an object. Light that is
predominantly from a preferred direction.