---
title: "Beer–Lambert law: meaning in gemology"
description: "The Beer–Lambert law says that the light a stone lets through falls off exponentially with path length: T = e^(−σℓ). Here σ is the absorption coefficient…"
url: https://digitalgemology.com/learn/glossary/beer-lambert-law
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Optics

# Beer–Lambert law

Also called Beer's law

The Beer–Lambert law says that the light a stone lets through falls off exponentially with path length: T = e^(−σℓ). Here σ is the absorption coefficient and ℓ is the path length.

## In more detail

A longer path deepens every absorption. So a large or deep stone looks darker than a thin slab of the same material.

## How we measure it

The simulator applies it per color channel along each internal path. The Dichroscope, Spectroscope and Polariscope apply it per wavelength along one straight path.

## Related terms

- [Absorption spectrum](https://digitalgemology.com/learn/glossary/absorption-spectrum): An absorption spectrum shows which wavelengths of light a stone absorbs. In a spectroscope, the absorbed parts of the spectrum look dark.
- [Pleochroism](https://digitalgemology.com/learn/glossary/pleochroism): Pleochroism is the property of a colored doubly refractive stone to show different colors in different directions. It happens because the stone absorbs its rays differently.
- [3D Gemstone Simulator](https://digitalgemology.com/learn/glossary/3d-gemstone-simulator): The 3D Gemstone Simulator is a free Digital Gemology tool that renders a cut stone as a camera sees it. You choose the cut, gemstone, carat weight, color, clarity, cut grade and lighting.

## Learn more

- [3D Gemstone Simulator](https://digitalgemology.com/about/how-we-measure/simulator)
- [Dichroscope](https://digitalgemology.com/about/how-we-measure/dichroscope)
- [Spectroscope](https://digitalgemology.com/about/how-we-measure/spectroscope)

[All 328 terms](https://digitalgemology.com/learn/glossary)