Prism Light Dispersion Simulator
See how a glass prism splits white light into a rainbow spectrum. Change the prism material, apex angle and angle of incidence, and get the refractive index and deviation angle for red and violet light.
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Why does a prism split white light into a rainbow?
White light is a mix of every color. When it goes into glass it slows down and bends, and the amount depends on the color: violet light slows down more than red light, so it bends more. This is called dispersion. A prism bends the light twice, once on the way in and once on the way out, so each color leaves at its own angle and the beam fans out into a spectrum. Isaac Newton split sunlight this way in the 1660s, and raindrops do the same thing when they make a rainbow.
Tool description
The Prism Light Dispersion Simulator traces a beam of white light through a prism, one wavelength every 2 nm from violet (400 nm) to red (700 nm). Pick the prism material, then move the sliders to change the apex angle, which is the angle at the top of the prism, and the angle of incidence, which is the angle between the beam and the dashed line square to the prism face. The beam stays white while its colors overlap and turns into a rainbow as they spread apart.
Under the diagram you get the refractive index and the deviation angle of red and violet light, and the spectrum spread, which is the angle between them. The refractive indexes come from published dispersion formulas: SCHOTT catalog data for crown glass, flint glass and dense flint, and fits of published measurements for water, fused silica, acrylic and diamond.
When light meets the far face of the prism too steeply, it can't get out and bounces back inside. This is total internal reflection. The diagram shows where that light goes, and the tool tells you which angle to change to let it out.
Features
- Ray tracing with Snell's law and total internal reflection at every face
- Seven prism materials, from water to diamond
- Refractive index, deviation and spectrum spread for red and violet light
How much a 60° prism spreads the colors
At the angle of minimum deviation, where the beam crosses the prism parallel to its base:
| Material | Refractive index | Angle of incidence | Spectrum spread |
|---|---|---|---|
| Water | 1.333 | 41.8° | 1.0° |
| Crown glass | 1.517 | 49.3° | 1.6° |
| Flint glass | 1.620 | 54.1° | 4.0° |
| Dense flint | 1.785 | 63.2° | 10.7° |
Flint glass spreads the colors much more than crown glass, which is why spectroscopes use flint glass prisms. Diamond bends light so strongly that no light gets out of a 60° diamond prism at all. Try an apex angle of 40° with an angle of incidence above 45°.