---
title: "Schlick's approximation: meaning in gemology"
description: "Schlick's approximation is a short formula for Fresnel reflectance: R(θ) = F0 + (1 − F0)(1 − cos θ)^5. F0 is the reflectance at normal incidence, ((n −…"
url: https://digitalgemology.com/learn/glossary/schlick-approximation
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Schlick's approximation

Also called Schlick Fresnel

Schlick's approximation is a short formula for Fresnel reflectance: R(θ) = F0 + (1 − F0)(1 − cos θ)^5. F0 is the reflectance at normal incidence, ((n − 1)/(n + 1))².

## In more detail

It is fast and close to the full Fresnel equations for unpolarized light. In our engine, F0 is 0.172 for diamond and 0.204 for moissanite.

## How we measure it

The Brightness & Tilt Analysis and the Cut Grading Tool's brilliance apply it at the entry and exit facets. The simulator uses the full Fresnel equations instead.

## Related terms

- [Fresnel reflection](https://digitalgemology.com/learn/glossary/fresnel-reflection): Fresnel reflection is the share of light that a surface reflects instead of letting through. The Fresnel equations give that share from the two refractive indices, the angle and the polarization.
- [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.
- [Refractive index](https://digitalgemology.com/learn/glossary/refractive-index): Refractive index is the speed of light in a vacuum divided by its speed in the stone. A higher index bends light more where it crosses a surface at an angle.

## Learn more

- [Brightness & Tilt Analysis](https://digitalgemology.com/about/how-we-measure/brightness-tilt)
- [Gemstone constants](https://digitalgemology.com/about/how-we-measure/gemstone-constants)

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