Sunlight is many colors

Shine white light into a prism

Sunlight looks white, but it is really many colors of light mixed together. Shine it into a triangular block of glass, called a prism, and the colors come out spread from red to violet. Each color bends by a slightly different amount in glass. A raindrop does the same thing.

Why?Light slows down when it enters glass or water, and it changes direction at the boundary. Violet light slows a little more than red light, so it bends a little more. The mixed colors then head off in slightly different directions.

Learn moreAround 1666, Isaac Newton showed that the colors split by a prism turn white again when you bring them back together, proving that white light is a mix of colors. In this prism, red bends by about 38.3° and violet by about 39.8°. That gap is small, so the picture spreads it 4 times wider.

Difference in bending, red vs. violet

1.5°

Red bends by

38.3°

Violet bends by

39.8°

calculated from the refractive index of water (IAPWS, 20 °C) and the laws of refraction and reflection