---
title: "CIE colorimetry: meaning in gemology"
description: "CIE colorimetry turns a light spectrum into a color by weighting it with standard human color-matching functions. Standard illuminants, such as D65…"
url: https://digitalgemology.com/learn/glossary/cie-colorimetry
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/learn/glossary/cie-colorimetry. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons.
> Site index: https://digitalgemology.com/llms.txt

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

# CIE colorimetry

Also called CIE 1931 observer, illuminant D65, illuminant A

CIE colorimetry turns a light spectrum into a color by weighting it with standard human color-matching functions. Standard illuminants, such as D65 (daylight) and A (incandescent lamp, 2856 K), define the light.

## In more detail

The CIE 1931 2° observer is the standard set of color-matching functions. A spectrum, an illuminant and the observer together give one reproducible color.

## How we measure it

The Dichroscope and Polariscope use the CIE 1931 observer with D65, at 81 wavelengths from 380 to 780 nm. The Spectroscope lets you choose illuminant A or D65.

## Related terms

- [CIEDE2000 color difference](https://digitalgemology.com/learn/glossary/ciede2000): CIEDE2000 (ΔE00) is a standard formula for how different two colors look to a human observer. A larger number means a larger visible difference.
- [Dichroscope](https://digitalgemology.com/learn/glossary/dichroscope): A dichroscope is a gem-testing instrument that shows a stone's two pleochroic colors side by side. In the calcite type, a calcite rhomb splits the light into two images of a small window.
- [Spectroscope](https://digitalgemology.com/learn/glossary/spectroscope): A spectroscope is a gem-testing instrument that spreads light from a stone into a spectrum. Dark lines and bands show where the stone absorbs.
- [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.

## Learn more

- [Dichroscope](https://digitalgemology.com/about/how-we-measure/dichroscope)
- [Spectroscope](https://digitalgemology.com/about/how-we-measure/spectroscope)
- [Polariscope](https://digitalgemology.com/about/how-we-measure/polariscope)

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