Marc proposes to burn a hole through a piece of cardboard using a magnifying glass and the sun. It doesn't harm the cardboard, but Lisa and Trini get the message.REHASHED FROM THE PREVIOUS FOUR EPISODES: Trini discovers a boy whose vision was improved with a cornea transplant. Trini uses a prism to split white light into the color spectrum. Lisa witnesses an infrared camera. Marc learns that butterflies and flowers bear ultraviolet light. Trini visits an observatory whose telescope studies the sun. ANIMATION: How the eye sees.ADDITIONAL: Lisa examines lasers. Marc encounters a solar-energy research lab.