Editing Absorbance (section)

=== Optics ===
In [[optics]], '''absorbance''' or '''decadic absorbance''' is the ''[[common logarithm]]'' of the ratio of incident to {{em|transmitted}} [[radiant power]] through a material, and '''spectral absorbance''' or '''spectral decadic absorbance''' is the common logarithm of the ratio of incident to {{em|transmitted}} [[Radiant power|spectral radiant power]] through a material. Absorbance is [[Dimensionless quantity|dimensionless]], and in particular is not a length, though it is a monotonically increasing function of path length, and approaches zero as the path length approaches zero.