Photometric quantities and units
From ColorWiki
Any radiometric measure can be converted to the corresponding photometric measure by computing the effect of the stimulus defined in radiometric terms on the CIE standard observer. This is defined by the spectral luminous efficiency curve V for photopic vision.
- Luminous Energy is the photometric quantity that corresponds to the radiometric quantity radiant energy
- is denoted by Qv
- its SI unit is the lumen seconds (lm s)
- Luminous Flux is the photometric quantity that corresponds to the radiometric quantity radiant flux
- is denoted by Pv
- its SI unit is the lumen (lm); 1 watt = 683 lumen
- Luminous Exitance is the photometric quantity that corresponds to the radiometric quantity radiant emittance
- is denoted by Mv
- its SI unit is the lux (lx)
- Illuminance is the photometric quantity that corresponds to the radiometric quantity irradiance
- is denoted by Ev
- its SI unit is the lumen per square meter (lm/m2)
- Luminous Intensity is the photometric quantity that corresponds to the radiometric quantity radiant intensity
- is denoted by Iv
- its SI unit is the candela (cd)
- Luminance is the photometric quantity that corresponds to the radiometric quantity radiance
- is denoted byv
- its SI unit is the candela per square meter (cd/m2)
For the purpose to investigating light and color, the most important photometric quantity is the luminance, because it is directly correlated with visual perception.
Bibliography
- G. Wyszecki, W.S. Stiles: Color Science: Concepts and Methods, Quantitative Data and Formulae Wiley 1982 (II ed.)
- CIE: International Lighting Vocabulary 1970 (III ed.)