Term: transmittance, \(T\), \(\tau\)
https://doi.org/10.1351/goldbook.T06484

Definition:
The ratio of the transmitted radiant power (P λ) to that incident on the sample (P λ 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.

Related Terms:
1) radiant power (http://doi.org/10.1351/goldbook.R05046).
2) absorbance (http://doi.org/10.1351/goldbook.A00028).
3) attenuance (http://doi.org/10.1351/goldbook.A00513).
4) beer–lambert law (http://doi.org/10.1351/goldbook.B00626).

Source: Green Book, 2nd ed., p. 32 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

Citation: 'transmittance, \(T\), \(\tau\)' 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

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