Editing Absorbance (section)

{{short description|Logarithm of ratio of incident to transmitted radiant power through a sample}}
{{About|a quantitative expression|the process itself|Absorption (electromagnetic radiation)}}
{{Redirect|Optical density|other uses|Refractive index|and|Nucleic acid quantitation|and|Neutral-density filter}}

'''Absorbance''' is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)".<ref name="GoldBook"/> Alternatively, for samples which scatter light, absorbance may be defined as "the negative logarithm of one minus absorptance, as measured on a uniform sample".<ref name=":0">{{GoldBookRef |title=decadic absorbance |file=D01536 }}</ref> The term is used in many technical areas to quantify the results of an experimental measurement. While the term has its origin in quantifying the absorption of light, it is often entangled with quantification of light which is "lost" to a detector system through other mechanisms. What these uses of the term tend to have in common is that they refer to a logarithm of the ratio of a quantity of light incident on a sample or material to that which is detected after the light has interacted with the sample.

The term [[Absorption (electromagnetic radiation)|absorption]] refers to the physical process of absorbing light, while absorbance does not always measure only absorption; it may measure [[attenuation]] (of transmitted radiant power) caused by absorption, as well as reflection, scattering, and other physical processes. Sometimes the term "attenuance" or "experimental absorbance" is used to emphasize that radiation is lost from the beam by processes other than absorption, with the term "internal absorbance" used to emphasize that the necessary corrections have been made to eliminate the effects of phenomena other than absorption.<ref name=":1" />