---
title: "Head shadow: meaning in gemology"
description: "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…"
url: https://digitalgemology.com/learn/glossary/head-shadow
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Head shadow

Also called observer 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.

## In more detail

A well-cut round sends much of its light back from straight overhead. So the head shadow causes a dip in return near face-up, and it draws the contrast pattern. Each tool uses its own head shadow, which is one reason their figures differ.

## How we measure it

Simulator: no light within 6°, fading back in by 10.5°. Brightness & Tilt Analysis: 0° to 30°, which you set; the default is 10°. Cut Grading Tool brilliance: 23°, after Hemphill et al. (1998) and Moses et al. (2004). Light census and Cut Grading Tool light maps: none.

## Related terms

- [Contrast (Light Return)](https://digitalgemology.com/learn/glossary/contrast): Contrast is the part of a face-up stone whose light comes from 75° or higher above the girdle plane. This zone lies within 15° of the line of sight, where the viewer's head is.
- [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.
- [ISO lighting](https://digitalgemology.com/learn/glossary/iso-lighting): 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.
- [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.
- [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.

## Learn more

- [Four light measures, side by side](https://digitalgemology.com/about/how-we-measure/light-measures)
- [Brightness & Tilt Analysis](https://digitalgemology.com/about/how-we-measure/brightness-tilt)
- [Cut Grading Tool](https://digitalgemology.com/about/how-we-measure/cut-grading-tool)
- [3D Gemstone Simulator](https://digitalgemology.com/about/how-we-measure/simulator)

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