Editing Absorbance (section)

===Absorbance of a material===
The '''absorbance''' of a material, denoted {{mvar|A}}, is given by<ref name="GoldBook">{{GoldBookRef|title=Absorbance|file=A00028|accessdate=2015-03-15}}</ref>

<math display="block">A = \log_{10} \frac{\Phi_\text{e}^\text{i}}{\Phi_\text{e}^\text{t}} = -\log_{10} T,</math>

where

* <math display="inline">\Phi_\text{e}^\text{t}</math> is the [[radiant flux]] {{em|transmitted}} by that material,
* <math display="inline">\Phi_\text{e}^\text{i}</math> is the [[radiant flux]] {{em|received}} by that material, and
* <math display="inline">T = \Phi_\text{e}^\text{t}/\Phi_\text{e}^\text{i}</math> is the [[transmittance]] of that material.

Absorbance is a [[dimensionless]] quantity. Nevertheless, the '''absorbance unit''' or '''AU''' is commonly used in [[ultraviolet–visible spectroscopy]] and its [[high-performance liquid chromatography]] applications, often in derived units such as the milli-absorbance unit (mAU) or milli-absorbance unit-minutes (mAU×min), a unit of absorbance integrated over time.<ref>{{cite web |author= GE Health Care |title= ÄKTA Laboratory-Scale Chromatography Systems - Instrument Management Handbook |date= 2015 |publisher= GE Healthcare Bio-Sciences AB |location= Uppsala |url= https://cdn.gelifesciences.com/dmm3bwsv3/AssetStream.aspx?mediaformatid=10061&destinationid=10016&assetid=16189 |archive-url= https://web.archive.org/web/20200315013424/https://cdn.gelifesciences.com/dmm3bwsv3/AssetStream.aspx?mediaformatid=10061&destinationid=10016&assetid=16189 |archive-date= 2020-03-15 }}</ref>

Absorbance is related to [[optical depth]] by

<math display="block">A = \frac{\tau}{\ln 10} = \tau \log_{10} e \,,</math>

where {{mvar|τ}} is the optical depth.