Transmittance
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In the fields of optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. The transmittance T (usually given as a percentage) of a sample is defined as
- <math>T% = I / I_0 * 100%<math>,
where <math>I_0<math> is the intensity of the incident light and I is the intensity of the light coming out of the sample. Transmittance is related to absorbance A as
- <math>A = 2 - \log_{10} T% = - \log_{10}T\,<math>
where T% is the percent transmittance and T is "per one" transmittance.
Note that the term transmission refers to the physical process of light passing through a sample, whereas transmittance refers to the mathematical quantity.