Photometry

luminous flux per solid angle in a given direction

science of the measurement of light in terms of perceived brightness

total amount of light energy flowing out of a light source per unit of time

alt=Illuminance diagram with units and terminology.|thumb|372x372px|Illuminance diagram with units and terminology In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance.

thumb|A tea light-type candle, imaged with a luminance camera; [[false colors indicate luminance levels per the bar on the right (cd/m2)]] Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle.

thumb|A photometer A photometer is an instrument for measuring photometric quantities such as luminous flux, illuminance, or luminance.

difference in luminance and/or color that makes objects visually distinguishable

thumb|Decreasing brightness with depth (underwater photo as example)

standard that defines a specific range of colors

measure of how well a light source produces visible light

description in optics of the angular dependency of the radiant intensity of a radiant surface

SI unit of luminance

scalar physical quantity

frame|right|Three hues in the Munsell color model. Each color differs in value from top to bottom in equal perception steps. The right column undergoes a dramatic change in perceived color.

unit of luminance; 10000/π candelas per square metre

unit of measurement; 10⁴ candela per square metre

spectral sensitivity of human visual perception of brightness

technical term

measure of illuminance for a combination of a camera's shutter speed and f-number

right|thumb|250px|The CIE 1931 color space|CIE 1931 xy chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature

Optical component

The apostilb is an obsolete unit of luminance. The SI unit of luminance is the candela per square metre (cd/m2). In 1942 Parry Moon proposed to rename the apostilb the blondel, after the French physicist André Blondel. The symbol for the apostilb is asb.

astronomical measure of the number of stars or galaxies per luminosity interval

model for determining radiant energy reflected off diffuse surfaces

reflectance reference used in photography

light in an optical system unintended by design

flame lamp used in photometry

form of easement in English law

oil lamp with a clockwork pump mechanism

A foot-lambert or footlambert (fL, sometimes fl or ft-L) is a unit of luminance in United States customary units and some other unit systems. A foot-lambert equals 1/ or 0.3183 candela per square foot, or 3.426 candela per square meter (the corresponding SI unit). The foot-lambert is named after Johann Heinrich Lambert (1728–1777), a Swiss-German mathematician, physicist and astronomer. It is rarely used by electrical and lighting engineers, who prefer the candela per square foot or candela per square meter units.

thumb|right|Manual (1), and Eilhard Mitscherlich|Mitscherlich's optical (2) goniometers for use in crystallography, c. 1900 A goniophotometer is a photometer for measuring the directional light distribution characteristics of light sources, luminaires, optical media, and surfaces. A goniophotometer typically incorporates a goniometer that measures direction using spherical coordinates to capture the angular distribution of the transmitted, emitted, or reflected light. A gonioradiometer differs only in that it is a radiometer (i.e., is not specific to human vision), rather than a photometer.

ratiometric definition of luminance

unit of measurement