Beer's law

noun

ˌbā(ə)rz-, ˌbe(ə)rz- 

: a statement in physics usually made in either of two mathematically equivalent ways: (1) the transmittance of a chemical solution is an exponential function of the product of the concentration of the solution and the distance light travels through it (2) the absorbance of a chemical solution is directly proportional to the product of its concentration and the distance light travels through it