C
candela, cd
the SI unit of luminous intensity, equal to one lumen per steradian (lm/sr).
ceiling
area lighting a general lighting system in which the
entire ceiling is, in effect, one large luminaire.
Note Ceiling area lighting
includes luminous ceilings and louvered ceilings.
ceiling
cavity the cavity formed by the ceiling, the plane of the
luminaires, and the wall surfaces between these two planes.
ceiling
cavity ratio (CCR) a number computed by using the distance from
the plane of the luminaire to the ceiling (hc) as Heightcavity in the equations
given for cavity ratio.
ceiling
projector a device designed to produce a well-defined illuminated
spot on the lower portion of a cloud for the purpose of providing a reference
mark for the determination of the height of that part of the cloud.
ceiling
ratio the ratio of the luminous flux reaching the ceiling
directly to the upward component from the luminaire.
channel an
enclosure containing the ballast, starter, lamp holders, and wiring for a
fluorescent lamp. Can also be a similar enclosure on which filament lamps
(usually tubular) are mounted.
chromatic
color perceived color possessing a hue. In everyday speech,
the word color is often used in this sense in contradistinction to white, gray,
or black.
chromatic
contrast threshold (color contrast threshold) a threshold of
chromaticity difference between two patches of color juxtaposed and separated
only by a color contrast border, below which they cannot be perceived as
different in chromaticness or separated by a contrast border. A contrast border
can involve differences both in luminance and in chromaticity between the
sides.
chromaticity
coordinates of a color, x, y, z the ratios of each of
the tristimulus values of the color to the sum of the three tristimulus
values.
chromaticity
diagram a plane diagram formed by plotting one of the three
chromaticity coordinates against another.
chromaticity
difference threshold the smallest difference in chromaticity
between two colors of the same luminance that makes them perceptibly different.
The difference can be a difference in hue or saturation, or a combination of
the two.
chromaticity of
a color 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.
chromaticness†
the attribute of a visual sensation according to which the (perceived) color of
an area appears to be more or less chromatic.
clear
sky
a sky that has less than 30% cloud cover.
cloudy
sky
a sky that has more than 70% cloud cover.
coefficient
of utilization (CU) the ratio of luminous flux (lumens)
calculated as 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. See Chapter 9, Lighting Calculations.
coffer a
recessed panel or dome in the ceiling.
cold-cathode
lamp
an electric-discharge lamp whose mode of operation is that of a glow discharge
and that has electrodes so spaced that most of the light comes from the
positive column between them.
color†
the characteristic of light by which a human observer can distinguish between
two structure-free patches of light of the same size and shape. See light
source color and object color.
color
rendering† 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 improvement (of a light source)† the adjustment of
spectral composition to improve color rendering.
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. See also correlated color temperature and distribution
temperature.
colorfulness of
a perceived color the attribute according to which it appears to exhibit more
or less chromatic color. For a stimulus of a given chromaticity, colorfulness
normally increases as the absolute luminance is increased.
cornice
lighting lighting comprising sources shielded by a panel parallel to the wall
and attached to the ceiling and distributing light over the wall.
correlated
color temperature (of a light source) (CCT) the absolute
temperature of a blackbody whose chromaticity most nearly resembles that of the
light source.
cosine
law
a law stating 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. The inverse square law and
the cosine law can be combined as E = (I cos θ)/d2. See cosinecubed
law and inverse square law.
cove
lighting comprising sources shielded by a ledge or horizontal
recess, and distributing light over the ceiling and upper wall.
cucoloris an
opaque cutout panel mounted between a light source (sun or arc) and a target
surface in order to project a shadow pattern (clouds or leaves are typical)
upon scenery, cyclorama, or acting area.
cutoff
angle (of a luminaire) the angle, measured up from nadir,
between the vertical axis and the first line of sight at which the bare source
is not visible.
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