Beer-Lambert Law

What is Beer-Lambert Law?

Beer-Lambert law has a modern definition which is a combination of two different laws and stated as for a given material sample path length and concentration of the sample are directly proportional to the absorbance of the light.

What is Beer’s Law?

Beer law states that concentration and absorbance are directly proportional to each other and it was stated by August Beer.

What is Lambert Law?

Lambert law states that absorbance and path length are directly proportional and it was stated by Johann Heinrich Lambert.

Beer-Lambert Law Equation

Beer-Lambert law equation is as follows:

\(\large I=I_{0}e^{-\mu (x)}\)


    I: intensity

    I0: initial intensity

    μ: coefficient of absorption

    x: depth in metre

Beer-Lambert Law Applications

This law finds applications in various fields such as:

  • Analytical chemistry: This analysis mainly concentrates on the separation, quantification and identification of matter by spectrophotometry. There is no involvement of extensive pre-processing of the sample to get the results. For example, bilirubin count in a blood sample can be determined by using a spectrophotometer.
  • In atmosphere: Solar or stellar radiation in the atmosphere can be described using this law. The law in atmospheric applications has a modified equation:
\(\large T=e^{-m(T_{a}+T_{g}+T_{RS}+T_{NO2}+T_{w}+T_{O3}+T_{r}+..)}\)


    a: aerosols

    g: mixed gases

    RS: Raman scattering effects

    NO2: Nitrogen dioxide

    w: water vapour absorption

    O3: Ozone

    r: Rayleigh scattering

Beer-Lambert Law Limitations

Using this law it becomes easy to study the absorptivity coefficient of the sample when the concentration is low ie; <10mM but as the concentration becomes high ie; >10mM there is a deviation as the electrostatic interactions become more.

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