Editing Absorbance (section)

===Spectral absorbance===
'''Spectral absorbance in frequency''' and '''spectral absorbance in wavelength''' of a material, denoted {{math|''A{{sub|ν}}''}} and {{math|''A{{sub|λ}}''}} respectively, are given by<ref name=GoldBook />

<math display="block">\begin{align}
A_\nu &= \log_{10} \frac{\Phi_{\text{e},\nu}^\text{i}}{\Phi_{\text{e},\nu}^\text{t}} = -\log_{10} T_\nu\,, \\
A_\lambda &= \log_{10} \frac{\Phi_{\text{e},\lambda}^\text{i}}{\Phi_{\text{e},\lambda}^\text{t}} = -\log_{10} T_\lambda\,,
\end{align}</math>

where

* <math display="inline">\Phi_{\mathrm{e},\nu}^t</math> is the [[Radiant flux|spectral radiant flux in frequency]] {{em|transmitted}} by that material;
* <math display="inline">\Phi_{\mathrm{e},\nu}^i</math> is the spectral radiant flux in frequency {{em|received}} by that material;
* <math display="inline">T_\nu</math> is the [[Transmittance|spectral transmittance in frequency]] of that material;
* <math display="inline">\Phi_{\mathrm{e},\lambda}^t</math> is the [[Radiant flux|spectral radiant flux in wavelength]] {{em|transmitted}} by that material;
* <math display="inline">\Phi_{\mathrm{e},\lambda}^i</math> is the spectral radiant flux in wavelength {{em|received}} by that material; and
* <math display="inline">T_\lambda</math> is the [[Transmittance|spectral transmittance in wavelength]] of that material.

Spectral absorbance is related to spectral optical depth by

<math display="block">\begin{align}
A_\nu &= \frac{\tau_\nu}{\ln 10} = \tau_\nu \log_{10} e \,, \\
A_\lambda &= \frac{\tau_\lambda}{\ln 10} = \tau_\lambda \log_{10} e \,,
\end{align}</math>

where
* {{mvar|τ{{sub|ν}}}} is the spectral optical depth in frequency, and
* {{mvar|τ{{sub|λ}}}} is the spectral optical depth in wavelength.

Although absorbance is properly unitless, it is sometimes reported in "absorbance units", or AU. Many people, including scientific researchers, wrongly state the results from absorbance measurement experiments in terms of these made-up units.<ref>{{cite journal |doi=10.1021/jz4006916 |title=How to Make Your Next Paper Scientifically Effective |journal=J. Phys. Chem. Lett. |date=2013 |volume=4 |pages=1578–1581 |issue=9|last1=Kamat |first1=Prashant |last2=Schatz |first2=George C. |pmid=26282316 |doi-access=free }}</ref>