 Absorbance

Absorbance is the dimensionless quantity $A={\log }_{10}(P_0/P)$, where $P_0$ and $P$ are reference and transmitted radiant powers at the chosen wavelength. For example, $A=1$ means one tenth of the reference power is transmitted. Under the Beer-Lambert law, absorbance can determine an absorbing species' concentration; attenuation by cloudiness or unrelated colored solutes needs separate controls. ^[ref]

Absorbance is a measure of how much light is absorbed by a sample when light passes through it. It is a dimensionless quantity used in various fields, notably in chemistry and biology, to quantify the concentration of a substance in a solution. Absorbance (A) is defined by the Beer-Lambert Law, which states that absorbance is directly proportional to the concentration of the absorbing species in the solution and the path length of the light traveling through the sample.