absorptance, α
[7.6.1] α = Φa/Φi The ratio of the absorbed flux to the incident flux. Note: The sum of the hemispherical reflectance, the hemispherical transmittance, and the absorptance is 1.0.
absorption
[7.6] A general term for the process by which incident flux is converted to another form of energy, usually and ultimately to heat. Note: All of the incident flux is […]
transillumination
[7.5.4] The process whereby a non-opaque surface is illuminated from the side opposite to that from which it is viewed.
bidirectional transmittance distribution function (BTDF)
[7.5.3.16] ft* The ratio of the differential luminance dLt(θt, ϕt) for a ray transmitted in a given direction(θt, ϕt) to the differential luminous flux density dEi(θi, ϕi), incident from a […]
transparent medium
[7.5.3.15.4] A medium in which the transmission is mainly regular and which usually has a high regular transmittance in the spectral range of interest.* Note: Objects may be seen distinctly […]
dichroic filter
[7.5.3.15.1] A filter that transmits certain wavelengths and reflects those not transmitted; the absorption is small over the wavelength band of interest.
filter
[7.5.3.15] A device for changing, by transmission or reflection, the magnitude and/or the spectral composition of the flux incident upon it. Filters are called selective (or colored) or neutral, according […]
opaque medium
[7.5.3.15.2] A medium that transmits no radiation in the spectral range of interest.* * International Lighting Vocabulary, CIE S 017/E:2011. Vienna, Austria: International Commission on Illumination; 2011.
translucent medium
[7.5.3.15.3] A medium that transmits visible radiation largely by diffuse transmission, so that objects are not seen distinctly through it.* * International Lighting Vocabulary, CIE S 017/E:2011. Vienna, Austria: […]
spectral transmittance
[7.5.3.14] τ(λ)=φτλ/φiλ The ratio of the transmitted flux to the incident flux at a particular wavelength, λ, or within a small band of wavelengths, Δλ, about Δ. Note: The various […]