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.

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 […]