| Definition: | spectral internal absorptance of a layer of an absorbing material such that the path of the radiation is of dimension length, and under conditions in which the boundary of the material has no influence Note 1 to entry: The unit of the quantity length has to be specified. If a new unit of length is used that is k times the magnitude of the original one, then the value of αi,o(λ)=1−τi,o(λ) will change to α′i,o(λ)=1−[τi,o(λ)]k. Note 2 to entry: The spectral absorptivity has unit one. Note 3 to entry: This entry was numbered 845-04-88 in IEC 60050-845:1987.
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