Separating light into its colors is called dispersion. The wavelength determines how much each color will bend. Red bends the least, violet the most. If the light beam strikes the prism at a certain angle, the amount of bending for each color is always the same. Each color then falls in exactly the same place on a screen, so its position is enough to identify it.
Scientists use the dispersive action of the prism in the spectroscope.
The spectroscope reveals that the spectral pattern of light is different for various classes of light sources. Light from the sun, from certain lamp filaments, and from molten metals each produces a spectrum which has all colors in an unbroken array. Such a pattern is called a continuous spectrum. Incandescent gases give off only certain colors, in fine lines. Their spectra are called bright-line spectra.