On a overhead projector, show the diagram of the electromagnetic spectrum . Be sure to mention that gamma rays and light are the same thing, it's just that gamma rays carry more energy than light and our eyes cannot see them. Both are waves, but gamma rays have a shorter wavelength and they oscillate faster than the type of light our eyes can see. Radio waves are also a form of light. They have a longer wavelength and oscillate slower than the type of light our eyes can see.
Someone is bound to ask if gamma rays move faster than light.
Pass out the cards. Either have them cut the cards out or have them check to make sure that they have a complete set. Review the values on the cards and go through a couple of examples of which would be brighter scenarios. Model the game.