The e-ILV provides free access to all the terms and definitions contained in the international standard CIE S 017:2020 ILV: International Lighting Vocabulary, 2nd edition.

To search for another term please use  "Back to the list" to return to the main page or the e-ILV.

For the complete set of terms and definitions CIE S 017:2020 can be purchased from the CIE Webshop. Members of a CIE National Committee or Associate National Committee have access to a 66,7 % discount on the purchase price of the standard.


basic law of radiometry and photometry

general principle that, in the absence of losses, the elementary radiant flux or luminous flux, dΦ, between two elementary areas dA and dA′ defining an elementary beam is proportional to the elementary projected areas dAcosθ and dA′cosθ ′ in the direction of the beam and inversely proportional to the squared distance, l, between the areas.

Note 1 to entry: The basic law of radiometry and photometry is expressed by

where the proportionality factor for this geometrical condition is equal to the radiance or luminance, respectively, within the elementary beam.

Note 2 to entry: The basic law of radiometry and photometry is based on the geometric extent.

Note 3 to entry: This entry was numbered 17-78 in CIE S 017:2011.

Publication date: 2020-12
Copyright © CIE 2020. All Rights Reserverd.