Hemispherical Reflectance, Absorptance, and Transmittance:
Hemispherical reflectance () is defined as the dimensionless ratio of the
radiant flux reflected from a surface to the radiant flux incident to it:
Hemispherical transmittance () is defined as the dimensionless ratio of the radiant
flux transmitted through a surface to the radiant flux incident to it:
Hemispherical absorptance () is defined by the dimensionless ratio of the radiant
flux absorbed by a surface to the radiant flux incident to it :
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i
reflected
i
transmittde
i
absorbed