Light changes speed as it moves from one medium to another. This speed change causes the light to be refracted and to enter the new medium at a different angle. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow. This can be used to separate a beam of white light into its constituent spectrum of colors.
Here a traditional prism and a cylindrical prism are used to provide a new perspective on everyday objects. Trees are flipped, lights are distored, and the ground meshes with the sky.