The Beer-Lambert Law of Spectroscopy relates the three main factors that control the amount of light of a given wavelength
that can pass from the source to the phototube of a spectrophotometer, or for that matter, the eye of an observer. It
is true everywhere on earth, and presumably, everywhere in normal space. It assumes that no other perturbations or other
variables are present, such as optically interfering substances (e.g., light-scattering particles or transparent, refractive
The three factors are
1. A, the Absorption Coefficient,
2. C, the concentration of the absorbing species,
3. L, the pathlength through which the ray of light passes from source to detector.
Thus, Beer-Lambert's relationship states that the amount of light absorbed along its path is directly proportional to
A, C and L.
LIGHT ABSORBED = A x C x L
Each chemical compound has its own characteristic set of Absorption Coefficients. The are wavelength-specific and
are ultimately determined by the electronic energy levels that are possible from that compound's molecular
The greater the value of the Absorption Coefficient at a given wavelength, the more electromagnetic energy at that wavelength
is absorbed when light passes through a dispersed population of that molecule (i.e., "darker colored" versus "weakly
The higher the concentration of absorbing particles within the light path, the more light is absorbed.
The longer the pathlength (i.e., the farther the light source is from the observer), the more light is lost through absorption.