Snell's law sets the direction of refracted light: n₁ sin θ₁ = n₂ sin θ₂. The angles are measured from the normal to the surface.
In more detail
Light bends toward the normal when it enters a material of higher index, and away from it when it leaves. When no angle satisfies the law, the light cannot leave and reflects totally.
How we measure it
Our light tracers refract rays by Snell's law. In doubly refractive stones, the simulator solves it for each of the two waves.
Related terms
- 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.
- 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).
- Total internal reflection: Total internal reflection happens when light inside a stone meets a facet beyond the critical angle. The facet then acts as a perfect mirror, and all the light reflects back into the stone.
- Ray tracing: Ray tracing follows straight lines of light through a model of a stone. At each facet it applies refraction and reflection, and it records where the light comes from or where it leaves.