This excellent site for elementary students (along with its sister site Optics for Teens) is produced by the Optical Society of America, a professional organization of scientists, educators and students. Both sites explore careers in optics and the science of light (in What is Optics? and Educational Articles) and have printable study guides for K-12 classrooms. But Optics for Teens, besides having a more subdued color scheme, has two don't-miss-them sections with interactive experiments: Optical Illusions and In the Lab.
Science Snacks are "miniature versions of some of the most popular exhibits at the Exploratorium" science museum of San Francisco. These fifty easy-to-do-at-home experiments involving light are arranged in alphabetic order from Afterimage to Water Sphere Lens. That should keep you busy for awhile, but when you are ready, you'll find more Science Snacks, organized by subject.