transmittance, T, τ

also contains definition of: internal transmittance
https://doi.org/10.1351/goldbook.T06484
The ratio of the transmitted radiant power (Pλ) to that incident on the sample (Pλ0): T=PλPλ0 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]
Citation: 'transmittance' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.T06484 RIS BibTex EndNote
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