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.

For advice on CIE Publications contact Note the CIE Helpdesk cannot assist with technical enquiries.


bi-directional reflectance distribution function


function describing the change with direction of irradiation, (θi,ϕi), and direction of view, (θr,ϕr), of the radiance of a surface element (xr,yr) in a given direction of view at a given wavelength λ, , with respect to the irradiance incident on the medium from the given direction of irradiation at the given wavelength, :

Note 1 to entry: The bi-directional reflectance distribution function is expressed in steradian to the power minus one (sr−1).

Note 2 to entry: See also "radiance coefficient".

Note 3 to entry: This entry was numbered 17-87 and 17-109 in CIE S 017:2011.

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