---
title: "Census ray classes: meaning in gemology"
description: "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."
url: https://digitalgemology.com/learn/glossary/census-ray-classes
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · How we measure

# Census ray classes

Also called useful ray, blink ray, grazing ray, lost ray

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.

## In more detail

Useful: out through the crown within 64° of vertical, after at least one pavilion reflection. Blink: out through the crown without touching the pavilion. Leak: out through the pavilion, or through the crown heading down; grazing: out through the girdle. Lost: out of the viewing cone, or still inside after 12 bounces.

## How we measure it

The exit facet and the exit direction set the class. Brilliance counts the useful rays, and fire counts the useful rays whose two colors leave more than 0.6° apart. The census “blink” class has nothing to do with blinking in a polariscope.

## Related terms

- [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.
- [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.
- [Leakage](https://digitalgemology.com/learn/glossary/leakage): Leakage is light that enters a stone and leaves where the viewer cannot see it, mostly through the pavilion. Lower leakage is better.
- [Blink (polariscope)](https://digitalgemology.com/learn/glossary/blink-polariscope): A stone blinks in a polariscope when it turns light and dark four times per turn between crossed polarizers. Blinking shows that the stone is doubly refractive.

## 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)

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