A rainbow can be made with a glass of water serving as a prism to break the light into different colors. Fill a glass and place it on a white sheet of paper. Set both in a window with sunlight shining through. Set an empty glass on a white sheet of paper beside the glass of water for comparison. If the sun's rays are strong enough, a faint rainbow will be seen against the paper sitting under the glass of water. Discuss what the water is doing to the light.
Place a glass prism in front of a sunbeam. Notice what happens to the light. The prism will make the light refract into the colors of the color spectrum. Notice in what order the colors occur. See if changing the angle of the prism changes the order of the colors in the spectrum.
Set a second prism upside down in front of the refracted rainbow - the light spectrum from the first prism. The second prism will combine the wavelengths together into white light again. Discuss what this means about light. Sir Isaac Newton wrote that it proved that white light was a combination of all the colors of the spectrum.
Light is created artificially as well as by the sun. View the light from florescent light bulbs, incandescent light bulbs and colored LED lights through a prism. Notice how the light spectrum changes. Speculate on why different light sources create somewhat different light spectrums. Check to see if a second prism recombines the light into white light. Prisms unlock the secrets of light.