Absorbance

In the optical absorbance or optical density of the perceptually logarithmic formulated opacity, and therefore a measure of the attenuation of a radiation (e.g., light), after passing through a medium. It is dependent on the wavelength of the radiation.

With the incident radiation and the radiation emerging describes the absorbance as a logarithmic size of the transmittance:

On the attenuation processes absorption, scattering, diffraction and reflection are involved in general. In analytical applications, see Lambert- Beer law, scattering and diffraction are often insignificant and the reflection losses are taken into account by spaces or parallel measurement. Then is spoken instead of absorbance of ( decadic ) absorbance (English absorbance ) or absorptivity, the standard-compliant designation is decadic absorbance.

Especially in physics there is also the definition of absorbance over the natural logarithm. In astronomy, the absorbance is measured in magnitudes.

The related to the path length, substance-specific Amount of attenuation is specified using the extinction coefficient and absorption coefficient.