Luminous coefficient

(optics) A measure of the fraction of the radiant power of a light source which contributes to its luminous properties, equal to the average of the luminosity function at various wavelengths, weighted according to the spectral intensity of the source. Also known as luminous efficiency.

Visual efficacy of visible radiation, a function of the spectral distribution of the source radiation in accordance with the “spectral luminous efficiency curve,” usually for the light-adapted eye or photopic vision, or in some instances for the dark-adapted eye or scotopic vision.

The spectral luminous efficiency of radiant flux is the ratio of luminous efficacy for a given wavelength to the value of maximum luminous efficacy. It is a dimensionless ratio. See also Illumination; Luminous efficacy; Photometry.

The luminous coefficient is a coefficient that measures the integrated fraction of the radiant power that contributes to its luminous properties as evaluated by means of the standard luminosity function.^[1] The luminosity coefficient is

where

y_λ is the standard luminosity function,

J_λ is the spectral power distribution of the radiant intensity.

The luminous coefficient is unity for a narrow band of wavelengths at 555 nanometres.

See also

• Luminous efficiency, the more common name for luminous coefficient
• Photometry

References

1. ^ Van Nostrand's Scientific Encyclopedia, 3rd Edition. Princeton, New Jersey, Toronto, London, New York: D. Van Nostrand Company, Inc.. January 1958. 

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