---
title: "Leakage: meaning in gemology"
description: "Leakage is light that enters a stone and leaves where the viewer cannot see it, mostly through the pavilion. Lower leakage is better."
url: https://digitalgemology.com/learn/glossary/leakage
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Leakage

Also called light leakage

Leakage is light that enters a stone and leaves where the viewer cannot see it, mostly through the pavilion. Lower leakage is better.

## In more detail

Leakage rises when pavilion facets are too shallow for the stone's critical angle. So stones with a refractive index below 2 usually leak more than diamond in the same cut. Each of our tools counts leakage in its own way. Compare leakage figures only within one tool and one gemstone.

## How we measure it

Light census (Cut Performance Wheel, cut pages and Index): the share of entering rays that leave through the pavilion. The Wheel's method page also counts rays that leave through the crown heading down. Brightness & Tilt Analysis: rays that leave below the horizon, find no exit, or stay inside after 12 bounces. That figure does not change with the head shadow. Simulator light map: light out through the pavilion, from below the horizon, or still inside after 18 bounces.

## Related terms

- [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.
- [Light map](https://digitalgemology.com/learn/glossary/light-map): A light map is a face-up picture of a cut stone, colored by the direction each point's light came from. Red is direct light, green is indirect light, blue is contrast, and a dark color is leakage.
- [Critical angle](https://digitalgemology.com/learn/glossary/critical-angle): The critical angle is the angle from a facet's normal beyond which light inside a stone reflects totally. It follows from the refractive index: θc = arcsin(1/n).
- [Windowing](https://digitalgemology.com/learn/glossary/windowing): A window is a face-up area through which you can see straight through a stone. It forms where pavilion facets are too shallow to reflect light, so light passes out of the back.
- [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.
- [Census ray classes](https://digitalgemology.com/learn/glossary/census-ray-classes): In our light census, every ray that enters a stone ends in one of five classes. The classes are useful, blink, leak, grazing and lost.

## Learn more

- [Cut Performance Wheel and cut-page scores](https://digitalgemology.com/about/how-we-measure/performance-wheel)
- [Digital Gemology Cut Performance Index](https://digitalgemology.com/learn/cut-performance-index)
- [Brightness & Tilt Analysis](https://digitalgemology.com/about/how-we-measure/brightness-tilt)
- [3D Gemstone Simulator](https://digitalgemology.com/about/how-we-measure/simulator)

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