---
title: "Light performance: meaning in gemology"
description: "Light performance is how well a cut stone handles light. We describe it with brilliance (light returned), fire (color) and scintillation (sparkle)."
url: https://digitalgemology.com/learn/glossary/light-performance
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/learn/glossary/light-performance. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons.
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[Glossary](https://digitalgemology.com/learn/glossary) · Light performance

# Light performance

Also called optical performance

Light performance is how well a cut stone handles light. We describe it with brilliance (light returned), fire (color) and scintillation (sparkle).

## In more detail

It depends on the cut's geometry and on the stone's refractive index and dispersion. A simulation of light performance describes a design, not a real stone. It is not a grading report.

## How we measure it

We measure it four ways: the light census, Brightness & Tilt Analysis, Cut Grading Tool and simulator. The census is behind the Cut Performance Wheel and the Index. The four answer different questions, so their numbers are not interchangeable.

## Related terms

- [Brilliance](https://digitalgemology.com/learn/glossary/brilliance): Brilliance is the white light that a cut stone returns to the viewer. In our census, it is the share of entering light that leaves through the crown toward the viewer.
- [Fire](https://digitalgemology.com/learn/glossary/fire): Fire is the flashes of spectral color that a cut stone sends out. In our census, fire is the share of returned light whose colors leave more than 0.6° apart.
- [Scintillation](https://digitalgemology.com/learn/glossary/scintillation): Scintillation is the pattern of light and dark flashes a stone shows as it, the light or the viewer moves. Our score reads it from the number of facets that reach the surface of the cut.
- [Light census](https://digitalgemology.com/learn/glossary/light-census): The light census is our ray tracer behind the Cut Performance Wheel, the cut-page scores and the Cut Performance Index. It drops a fixed set of rays on a stone from above and counts where each one leaves.
- [Light Return](https://digitalgemology.com/learn/glossary/light-return): Light Return sorts each point of a face-up stone by the direction its light came from. Its four classes, direct, indirect, contrast and leakage, together cover the whole face-up stone.
- [Overall score](https://digitalgemology.com/learn/glossary/overall-score): The overall score is one figure out of 100 that combines our light-performance scores for one cut in one gemstone. The Cut Performance Wheel calls it Global.

## Learn more

- [Four light measures, side by side](https://digitalgemology.com/about/how-we-measure/light-measures)
- [How we measure](https://digitalgemology.com/about/how-we-measure)

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