Think about this!
Molecules changing from one form to another is not the only type of reaction that photochemistry can bring about. Below are two pictures of the same ball. The picture on the left is taken in the light. The picture on the right is taken in the dark. Light energy is absorbed by the molecules on the ball. These molecules are now in an "excited" state because of the extra energy they have. In order to release this energy they emit light, causing the stars on the ball to glow in the dark! Why do only the stars glow in the dark?