# Beer-Lambert law

**Definition**

*noun*

The principal law in spectrometry in which it states that the absorbance at a given wavelength of light is proportional to the molar extinction coefficient, the concentration of absorbers in the sample of the molar solution, and the length of the light path

**Supplement**

According to the Beer-Lambert law, the absorbance at a given wavelength of light (A) is proportional to the molar extinction coefficient (E), the concentration of absorbers in the sample of the molar solution (C), and the length of the light path (L), thus, the equation, A = ECL. Or, simply put, the concentration of a substance in moles is proportional to the absorption of a given wavelength of light by a solution of the substance. It is regarded as the principal law in spectrometry^{1}, and is used in the study of spectroscopy.

The law was discovered by Pierre Bouguer and attributed to Johann Heinrich Lambert. August Beer extended the exponential attenuation law by including the concentration of solutions in the attenuation coefficient.^{2}

*Also called:*

- Lambert–Beer law
- Beer–Lambert–Bouguer law

*See also:*

- spectrometry
- Molar absorption coefficient
- Extinction coefficient
- Molar absorptivity
- Molar extinction coefficient
- Molar absorbancy index

*Reference(s):*
^{1} Svanberg, S. (2004). Atomic and molecular spectroscopy : basic aspects and practical applications. Berlin New York: Springer.
^{1} Beer (1852) "Bestimmung der Absorption des rothen Lichts in farbigen Flüssigkeiten" (Determination of the absorption of red light in colored liquids), Annalen der Physik und Chemie, vol. 86, pp. 78–88.