Beer Lambert Law Definition

Discover the significance of the Beer Lambert Law in chemistry and physics, how it is applied in spectrophotometry, and its importance in various industries.


The Beer-Lambert Law, also known as Beer’s Law, is a fundamental principle in the field of chemistry and physics that relates the absorption of light to the properties of the material through which the light is passing. This law is essential in various scientific disciplines and is used in spectrophotometry, colorimetry, and other analytical techniques.

Understanding the Beer Lambert Law

The Beer-Lambert Law states that the absorbance of a sample is directly proportional to its concentration and path length. Mathematically, it can be expressed as A = εlc, where A is the absorbance, ε is the molar absorptivity or molar extinction coefficient, l is the path length of the sample, and c is the concentration of the sample.

Application in Spectrophotometry

Spectrophotometry is a technique that measures how much a substance absorbs light by passing a beam of light through a sample and measuring the intensity of light that emerges on the other side. The Beer-Lambert Law is used to determine the concentration of a solution by measuring its absorbance at a specific wavelength.


For example, if a solution with a concentration of 0.1 M has an absorbance of 0.5 at a particular wavelength and a path length of 1 cm, the molar absorptivity would be 5 (0.5/0.1) and can be used to determine the concentration of an unknown sample using the Beer-Lambert Law.

Case Study

In a study conducted by researchers to quantify the amount of a specific compound in a water sample, the Beer-Lambert Law was used to establish a calibration curve by measuring the absorbance of standard solutions with known concentrations. The calibration curve was then used to determine the concentration of the compound in the water sample.


According to research, the Beer-Lambert Law has been utilized in various industries, including pharmaceuticals, environmental monitoring, and food analysis, to quantify the concentration of substances in a sample accurately. The reliability and simplicity of this law make it an essential tool in analytical chemistry.

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