In order to get white light from the dispersed light the prisms are arranged as shown in the diagram. Recombination of the seven colours of the dispersed white light to get white light is known as recomposition of white light.
Experiment to Show the Recomposition of White Light
Place a prism (P1) on a table and a screen behind it. Allow a narrow beam of light to be incident on the prism (P1). The white light gets dispersed and we obtain a band of seven colours on the screen.
Now remove the screen and place another prism P2 of the same material in the opposite direction. Place a white screen behind P2. A spot of white light appears on the screen. Thus the second prism has recombined the dispersed light.
