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In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample.

\mathcal{T} = {I\over I_{0}}

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

A = - \log_{10}\mathcal{T}\ = - \log_{10}\left({I\over I_{0}}\right)

or, using the natural logarithm

A = - \ln\mathcal{T}\ = - \ln\left({I\over I_{0}}\right)

From the above equation and the Beer-Lambert law, the transmittance is thus given by

\mathcal{T} = e^{-\alpha \, x},

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.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Transmittance". A list of authors is available in Wikipedia.
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