Transmittance
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In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample.
where I0 is the intensity of the incident light and I is the intensity of the light coming out of the sample. The transmittance of a sample is sometimes given as a percentage.
Transmittance is related to absorbance A as
or, using the natural logarithm
From the above equation and the Beer-Lambert law, the transmittance is thus given by
- ,
where α is the attenuation coefficient and x is the path length.
Note that the term "transmission" refers to the physical process of light passing through a sample, whereas transmittance refers to the mathematical quantity.