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That light which when incident on a material is neither reflected nor transmitted.
Described as having no color (or hue) for example a neutral white, grey or black color.
Additive Primary Color
The additive primary colors are Red, Green & Blue. When equal amounts of light of the three additive primary colors is combined, white light is generated. Combining two additive primaries in equal amounts creates a subtractive primary color. See also: Subtractive Primary Color.
A unit of wavelength of light. One Angstrøm (Å) is 0.1 nm (or 10-10 m).
Multiples of light-sensitive elements in cameras, detectors or scanning devices. 
Average (Luminous) Intensity 
Applies to LEDs. The near-field luminous intensity for a non point source. Defined in CIE document 127 as being the intensity (luminous flux per unit solid angle) measured by a photodetector with an input area of 100 mm2 positioned at either 316mm (condition A) or 100 mm (condition B) from the tip of the LED source, measured on the mechanical axis of the LED. Average luminous intensity has units of candela (cd).


See: Linewidth.
The (near) complete absorption of light as a result of no (low) reflectance. In colorimetry, describes a color of low saturation and low luminance.
Blackbody Radiation
Radiation that is full or complete, containing all wavelengths. The spectral power distribution of light emitted from a blackbody is a function of its temperature only and is described by Planck’s law. See also: Color Temperature.
Blackbody Radiator
A source that emits blackbody radiation.
That attribute of visual perception that describes the degree to which an object emits or reflects light. In colorimetry, brightness is used in the HSB color model – Hue, Saturation and Brightness. Describes the lightness of the color, on a scale ranging from black to white. Can be confused with saturation hence its use is discouraged. Can also be used instead of luminance – again its use is not recommended.


The SI base unit used in photometry. The candela is the unit of luminous intensity. The candela is one of the seven base units of the SI system. Since 1979, the candela has been defined as: “the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 Hertz and has a radiant intensity in that direction of 1/683 Watts per steradian” (where the steradian is the unit of solid angle).
Candle Power
The luminous intensity of a light source having units of candelas.
Catadioptric Imaging System
A system that uses both reflection and refraction to achieve its focal power. While the relative powers of the lenses and mirrors vary from system to system, the use of the reflective surfaces to achieve most of the power, in combination with refractive surfaces of little or zero power, produces an image that has improved aberrational characteristics.
Color Balancing Filter Sets
Stands for Charge Coupled Device. A monolithic, two-dimensional semiconductor (silicon-based) detector array. When illuminated by optical radiation in the range between approximately 300 and 1100 nm, produces a photocurrent, the magnitude of which is proportional to the level of light received. Each detector in the array is called a pixel.
Stands for Compact Fluorescent Lamp. See also: Fluorescent Lamp.
Color Glass Filter Set
The lightness of a color, denotes the degree of lightness or darkness. See also: Lightness.
Described as having color (or hue) – not white, grey or black.
In colorimetry, describes the intensity or level of saturation of a color (hue) defined as the distance in the particular color space of a color from the neutral grey color with the same value.
Chromaticity Coordinates (CIE)
A numeric descriptor of color. Defined as the ratio of the three tristimulus values XYZ in relation to the sum of the three, designated by xyz respectively. It is normal to assume that the chromaticity coordinates refer to the CIE 28 observer (1931). For reflected color, it is assumed to be calculated for standard illuminant C unless specified differently. See also: x, y, u’, v’.
Chromaticity Diagram (CIE)
The two-dimensional graph which plots the chromaticity coordinates. For the CIE 28 observer (1931) x is plotted as the abscissa, y as the ordinate. The color space plots the spectrum locus of monochromatic radiation in the spectral range 380-770 nm.
The International Commission on Illumination (Commission Internationale de l’Eclairage). Formed in 1924, the primary international body responsible for the science of photometry and colorimetry.
CIE 1976 L*a*b* Color Space
A uniform color space adopted by CIE in 1976 that is used in the measurement of small (normally reflected or transmitted) color differences.
CIE 1976 L*u*v* Color Space
A uniform color space adopted by CIE in 1976 that is used when measuring the color as a result of additive mixing from emitters of light.
CIE Luminosity Function (Y)
See: Photopic Response.
CIE Standard Illuminant
Standard source spectral power distributions as defined by CIE for four types of light source. See Illuminant A, B, C & D.
CIE Standard Observer Function
See: Photopic Response.
The color space within which L*a*b* color coordinates are plotted using a Cartesian coordinate system. This color space plots equal color differences at approximately equal distances. The L* value denotes the lightness, a* represents the red/green axis, while b* represents the yellow/blue axis. CIELAB is that color space used in relation to the measurement of reflected or transmitted color.
Calibrated Luminous Flux Standards - Set of 3
Acronym standing for Cyan, Magenta, Yellow & Black. See also: Subtractive Primary Color.
Color Temperature
A colorimetric concept related to the apparent visual color of a source (not its temperature). For a blackbody, the color temperature is equal to the temperature in kelvin.
An instrument that measures the color of the light it receives. Applies to instruments that measure reflected (transmitted) light as well as to those that analyze the light emitted by a source. Applies to instruments that use RGB optical filters to mimic as close as possible the tristimulus color response of the human eye. See also: tristimulus.
The science of measuring the color of light (emitted, reflected or transmitted) from an object with a spectral response matching that of the human eye. See also: tristimulus.
Can be described as being one aspect of an object’s appearance. In colorimetry, color is a