Splitting white light into a rainbow with a prism is one of the most beautiful science demonstrations available — and it's surprising how many children (and adults) have never seen it done. The rainbow appears because different wavelengths (colors) of light bend by different amounts when they pass from air into glass or water. The result — white light "exploding" into a perfect spectrum of colors — reveals that white light contains all colors at once, invisible until separated.

Rainbow-Making Methods

• Glass of water: Place a clear glass of water on a white piece of paper in direct sunlight. A rainbow will appear on the paper as sunlight refracts through the water.
• CD / DVD: Hold a CD in sunlight and tilt it — rainbow colors appear in the shiny surface through diffraction.
• Glass prism: The classic method — hold a triangular glass prism in direct sunlight and project the spectrum onto a white wall.
• Hose spray: On a sunny day, stand with the sun behind you and spray a fine mist with a garden hose — a personal rainbow appears in the mist in front of you.

Frequently Asked Questions

Why does a prism split white light into colors?

White light is a mixture of all visible wavelengths — from violet (shortest, ~400nm) to red (longest, ~700nm). When light passes from air into glass, it bends (refracts). Crucially, the amount of bending depends on wavelength: violet bends more than red. So a prism bends each color by a different amount, spreading them apart. This color spreading is called dispersion. Rainbows form the same way — tiny water droplets in the air act as millions of tiny prisms.

Related activities: Rainbow Hunt | Shadow Investigation | Balloon Static Electricity