transmittance \(T\), \(\tau\)

Also contains definition of: internal transmittance
https://doi.org/10.1351/goldbook.T06484
The ratio of the transmitted @R05046@ (\(P_{\lambda }\)) to that incident on the sample (\(P_{\lambda }^{0}\)): \[T=\frac{P_{\lambda }}{P_{\lambda }^{0}}\] Internal transmittance refers to energy loss by absorption, whereas the total transmittance is that due to absorption, reflection, scatter, etc.
See:
absorbance
,
attenuance
,
Beer–Lambert law
Sources:
Green Book, 2nd ed., p. 32 [Terms] [Book]
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2281 [Terms] [Paper]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 996 [Terms] [Paper]