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Split white light into a rainbow with a glass prism.
Prism Rainbow lab · Last updated: 16 October 2026
A beam of white light shines into a triangular glass prism and comes out as a fan of colours: red, orange, yellow, green, blue and violet. You turn the prism and explore where those colours come from.
What you'll discover
- White light is a mixture of all the colours of the rainbow.
- A prism bends each colour by a slightly different amount, so they spread apart.
- Violet bends the most and red the least, which fixes the order of colours.
The science in plain words
Sunlight and the light from a white lamp look colourless, but they are really a mixture of many colours. In 1666 Isaac Newton showed this by passing sunlight through a prism and spreading it into a band of colours, called a spectrum. He then used a second prism to recombine the colours into white light.
A prism works by refraction. Light slows down and bends when it enters glass, and bends again when it leaves. The key point is that glass slows different colours by slightly different amounts. Violet light is slowed the most, so it bends the most; red light is slowed the least, so it bends the least. The colours separate, and the triangular shape of the prism bends them further at the second face, so the fan spreads wider.
This splitting of light into colours is called dispersion. The order is always the same: red, orange, yellow, green, blue, indigo and violet.
A rainbow in the sky is made in a similar way. Each raindrop acts like a tiny prism, refracting sunlight, reflecting it inside the drop and spreading it into colours.
Where it fits
- India, NCERT: Class 10 science, Chapter 10: The Human Eye and the Colourful World
- United States: Grades 6 to 8
- Next Generation Science Standards: MS-PS4-2
Common questions
How does a prism make a rainbow?
White light is a mix of colours. Glass bends each colour by a slightly different amount, so as light passes through the prism the colours fan out into a spectrum.
Why does violet light bend more than red?
Glass slows violet light a little more than red light. The more light slows down when entering glass at a slant, the more it bends.
How are rainbows formed?
Sunlight enters raindrops, bends, reflects off the back of each drop and bends again on the way out. Each colour leaves at a slightly different angle, so we see bands of colour.
Related labs
- Bending Light: Shine a ray into a glass block. How much does it bend?
- Rainbow and Beyond: Slide from ultraviolet through the rainbow to infrared. Which light makes the star glow?
- Candle, Lens and Screen: Slide the screen until the candle is sharp. Why is its picture upside down?
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Try it yourself
The Prism Rainbow lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.