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luminance Dictionary Terms

luminance range
An objective measure of an object's brightness that is derived from the ratio of the luminance of its lightest section to...
binocular threshold
The absolute luminance threshold for detection by the two eyes.
photometric cube
A prism used in a photometer for the adjacent comparison of separate luminance.
negative glow
In a cold-cathode tube, the luminance between the cathode dark space and the Faraday dark space. In a vacuum tube, the...
illumination
The general term for the application of light to a subject. It should not be used in place of the specific quantity...
uniform luminance area
In a cathode-ray tube, the region wherein a display on the tube keeps 70 percent or more of its luminance at the center of...
luma
The luminance portion of a composite video signal, i.e., the portion of the signal that corresponds to the brightness of the...
image brightness
The apparent luminance of the image as seen through an optical system. This brightness of the image is determined by the...
footlambert
Unit of luminance equal to 1/p candela per square foot. (fl).
scotopic vision
Vision by means of retinal rods; vision of the dark-adapted eye. In scotopic vision, the level of luminance is so low that...
photometric equipment
Photocells of various kinds used to measure photometric quantities; i.e., intensity, luminance and illuminance. Meter...
mesopic vision
Vision at intermediate levels of luminance between photopic and scotopic vision, where both retinal cones and retinal rods...
telephotometer
An instrument used to measure the luminance (brightness) of a distant object. The object is viewed through a small...
troland
That level of retinal illuminance resulting when a surface with a luminance of 1 candela/m2 is viewed through a pupil with...
highlight
The portion of a reproduced image having the greatest luminance.
Ferry-Porter law
The law stating that the critical fusion frequency is approximately proportional to the logarithm of the luminance and the...
inverse square law
The law stating that the illuminance (or irradiance) from a point source varies as the inverse square of the distance...
contrast
The apparent difference in brightness between light and dark areas of an image. For a light target against a dark...
flicker photometry
Heterochromatic photometry that depends on the elimination of chromatic flicker at a lower frequency than luminance flicker.
photometer
A device used to compare the luminous intensities of two sources by comparing the illuminance they produce.
receiver primaries
Also known as display primaries. Colors formed by a television receiver that are of constant chromaticity and variable...
Craik-O'Brien effect
Observed when alterations in the luminous sterance at the contour of an object create the illusion of the outer zones...
absolute luminance threshold
The minimum value of luminance for vision. The value may vary with age as well as dark adaption period. (Measured range...
Liebmann effect
The visual perception of contrasting forms is more difficult if the forms have the same luminance but different...
visual photometer
A photometer that permits visual comparison of the luminance of two surfaces.
sine wave object
An object that has a sinusoidal variation of luminance. Its image will have a sinusoidal variation of illuminance and the...
comb filter
A filter that passes a series of wavelength regions that are at equal distances from one another, such that its output...
photochromatic interval
The discrepancy between the absolute luminance threshold and the photochromatic threshold.
colorimetric purity
Ratio, to the luminance of a test color, of the luminance of the spectrum color that matches the test color when mixed with...
photopic vision
Vision by means of retinal cones; color vision. Relatively high levels of luminance are required for photopic vision.
high-gain screen
A screen with a reflected or transmitted light beam that is confined to a much smaller bundle than was received by the...
illuminance
Luminous flux incident per unit area of a surface; luminous incidence. (The use of the term "illumination" for...
luminance factor
Ratio of the luminance of a specimen to that of a perfect reflecting or transmitting diffuser identically illuminated.
nit
Unit of measurement of brightness (luminance) equal to one candela per square meter.
etendue
A product of the area of a light beam (normal to its direction of propagation) and the solid angle that the beam includes;...
composite video
A type of video signal in which the luminance and chrominance portions of the signal, or the luma and chroma, have been...
photon counter
A device used to evaluate the luminance of a surface by determining the number of photons emitted from a sample surface area.
cosine law of illumination
Law relating the illuminance (or irradiance) of a surface to the cosine of the angle, q, between the normal to the surface...
cascade method
A heterochromatic photometric process using successive comparison of similar chromaticities and the calculation of relative...
atmospheric attenuation
The reduction in luminance of a light beam due to absorption and scattering as it passes through the atmosphere.
cathode dark space
The area of low-level luminance lying between the cathode and the negative glow in a glow-discharge, cold-cathode tube.
heterochromatic photometry
Light measurement by comparison of the luminances of unlike chromaticities.
luminance meter
A type of photometer calibrated in luminance units (candles per square unit, or lamberts). In photography an exposure meter...
apparent luminance
The perceived brightness of an object being viewed at some distance, especially through an optical instrument.
footcandle
Unit of illuminance equal to one lumen per square foot. (fc).
nox
Equal to 10-3 lux; used in measuring low values of illumination and luminance.
chrominance
The difference between any color and a reference color having equal luminance and a specified chromaticity.
Strehl ratio
The ratio of the illuminance at the peak of the diffraction pattern of an aberrated point image to that at the peak of an...
background luminance
The intensity of the light in the scene behind an object being viewed.
vignetting
In an optical system, the gradual reduction of image illuminance as the off-axis angle increases, resulting from limitations...
brightness meter
An instrument for measuring the brightness (luminance) of a scene. It may be a spot meter, covering an area of a degree or...
constant luminance encoder
A device used in broadcast CCD cameras to improve definition in heavily saturated colors by band-limiting the color...
Fechner ratio
The differential luminance threshold divided by the luminance.
equiluminous colors
Colors differing only in chromaticity but not in luminance.
dark discharge
In a gas, an electrical discharge that has no luminance.
sine wave testing chart
A test chart whose luminance changes uniformly in one direction according to a sinusoidal rule. These charts carry groups of...
stilb
A unit of luminance that is equal to one candela/cm2. (sb).
microphotometer
An instrument capable of measuring the transmitted or reflected luminance from a very small area seen under a microscope....
luminance
Luminous flux emitted from a surface per unit solid angle per unit of area, projected onto a plane normal to the direction...
lambert
A unit of luminance equal to 1/p candela per square centimeter. (l).
lambertian surface
A perfectly diffusing surface; the intensity of the light emanating in a given direction from any small surface component is...
photographic exposure
The product of exposure time and irradiance or illuminance.
additivity of luminance
The luminance of a mixture of lights is the sum of the luminances of the component lights in the mixture.
apostilb
A unit of luminance equal to 1/p candela per square meter.
Lambert's cosine law
Flux per unit solid angle leaving a surface in any direction is proportional to the cosine of the angle between that...
lux
SI unit of luminous incidence or illuminance, equal to 1 lumen per square meter.

(66 results found)

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