A beam of white light, as from the sun, strikes a prism made of flint glass. Flint glass has a high refractive index and a high dispersion (spread). Shorter wavelengths (blue) are refracted more than the longer wavelengths (red), causing the beam to split into a rainbow or spectrum. This animation is a simulation and the prism becomes flatter and wider, illustrating how the refraction and dispersion increase with the widening.