When _______ light passes through a prism or diffraction grating, its component colors are separated and one can distinguished them like the colors of the rainbow.

White light is defined as the complete mixture of all of the wavelengths of the visible spectrum. This means that if I have beams of light of all of the colors of the rainbow and focus all of the colors onto a single spot, the combination of all of the colors will result in a beam of white light

White light can be separated into all seven major colors of the complete spectrum or rainbow by using a diffraction grating or a prism. The diffraction grating separates light into colors as the light passes through the many fine slits of the grating. This is a transmission grating. There are also reflection gratings.