bidirectional scatter distribution function (BSDF)

[7.2.2] The general mathematical function or matrix of data that describes the directional scattering of light by a surface or complex glazing system through both reflection and transmission across input […]

visible transmittance

[] VT or Tvis The fraction of incident light that is transmitted through a material.  Also known as visible light transmittance (VLT).

specular reflectance

[] The ratio of the flux leaving a surface or medium by specular reflection to the incident flux. Also called regular reflectance. NOTE: This term and its definition were changed […]

specular reflection

[7.3.1] That process by which incident flux is redirected at the specular angle (see bihemispherical reflectance). Also called regular reflection. NOTE: This term and its definition were changed in RP-16-17 […]

linear polarization

[7.8.2] The process by which the transverse vibrations of light waves are oriented in or parallel to the same plane. Polarization may be obtained by using either transmitting or reflecting […]

luminance factor, β

[7.7] The ratio of the luminance of a surface or medium under specified conditions of incidence, observation, and light source, to the luminance of a completely reflecting or transmitting, perfectly […]


[7.8] The process by which unpolarized radiation becomes polarized. It can be accomplished by reflection and/or transmission processes. (See polarized radiation.)

polarized radiation

[7.8.1] Radiation whose electromagnetic field, which is transverse, is oriented in defined directions. The polarization can be rectilinear, elliptical, or circular.