AskDefine | Define transmittance

Dictionary Definition

transmittance n : the fraction of radiant energy that passes through a substance [syn: transmission]

User Contributed Dictionary



  1. a transmission
  2. the fraction of incident light, or other radiation, that passes through a substance


fraction of incident radiation
  • German: Transmissionsgrad
  • Italian: trasmittanza
  • Korean: 투과율

Extensive Definition

In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample.
\mathcal =
where I_0 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_\mathcal\ = - \log_\left(\right)
or, using the natural logarithm
A = - \ln\mathcal\ = - \ln\left(\right)
From the above equation and the Beer-Lambert law, the transmittance is thus given by
\mathcal = e^,
where \alpha 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.
transmittance in Czech: Transmitance
transmittance in German: Transmission (Physik)
transmittance in Spanish: Transmitancia
transmittance in French: Transmittance
transmittance in Italian: Trasmittanza
transmittance in Portuguese: Transmissão (física)
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