---
title: "ISO lighting: meaning in gemology"
description: "ISO is a dome model that lights the stone evenly from every direction above the horizon. It asks only how much light comes back, not from where."
url: https://digitalgemology.com/learn/glossary/iso-lighting
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/learn/glossary/iso-lighting. 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) · How we measure

# ISO lighting

Also called ISO dome, isotropic dome

ISO is a dome model that lights the stone evenly from every direction above the horizon. It asks only how much light comes back, not from where.

## In more detail

It is the most forgiving of the three dome models. The definition follows Robert W. Strickland's GemRay user guide; the implementation is our own.

## How we measure it

In the Brightness & Tilt Analysis, ISO gives every direction above the horizon the weight W = 1. The weight is 0 inside the head shadow. The Cut Grading Tool's brilliance is the ISO figure with a 23° head shadow, averaged over 13 tilts.

## Related terms

- [Dome model](https://digitalgemology.com/learn/glossary/dome-model): A dome model is an idealized light source: a dome over the stone that weights light by its elevation. Our Brightness & Tilt Analysis uses three dome models: ISO, COS and SC2.
- [COS lighting](https://digitalgemology.com/learn/glossary/cos-lighting): COS is a dome model in which light is brightest overhead and fades to zero at the horizon. Each direction is weighted by the sine of its elevation.
- [SC2 lighting](https://digitalgemology.com/learn/glossary/sc2-lighting): SC2 is a dome model with a ring of light that peaks at 45° elevation. It is dark overhead and at the horizon.
- [Brightness & Tilt Analysis](https://digitalgemology.com/learn/glossary/brightness-and-tilt-analysis): The Brightness & Tilt Analysis is a free Digital Gemology tool. It measures how much dome light a cut returns face-up, and how this changes with tilt.
- [Head shadow](https://digitalgemology.com/learn/glossary/head-shadow): The head shadow is the part of the overhead light that the viewer's own head blocks. In our tools, it is a cone around the line of sight in which no light counts.
- [Cut Grading Tool](https://digitalgemology.com/learn/glossary/cut-grading-tool): The Cut Grading Tool is a free Digital Gemology tool that grades a round brilliant diamond's cut from its proportions. It reads GIA's published cut grade estimation tables; it is for education and does not give a GIA grade.

## Learn more

- [Brightness & Tilt Analysis](https://digitalgemology.com/about/how-we-measure/brightness-tilt)
- [Brightness & Tilt Analysis](https://digitalgemology.com/tools/brightness-tilt-analysis)
- [Cut Grading Tool](https://digitalgemology.com/about/how-we-measure/cut-grading-tool)

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