The sun is the source of light on planet Earth. It produces electromagnetic energy that travels at light speed—186,000 miles per second. Fiber optic technology has harnessed this speed to carry voice, data, and images over glass threads faster and farther than ever before. Our eyes are natural light collectors. When light enters the eyes, it reaches the retina, where special cells turn it into electrical impulses that the brain interprets. Our eyes can only see a fragment of the electromagnetic spectrum, the part called the visible spectrum. Outside the visible spectrum are other waves of varying length and frequency, from short waved gamma rays to radio waves, which are the longest. We need special equipment to detect electromagnetic waves outside the visible spectrum. For example, radio telescopes pick up cosmic radio waves. The Hubble Space Telescope detects infrared radiation. Some creatures make their own light, called bioluminescence. Some five hundred feet beneath the ocean surface, creatures use bioluminescence to help them see, avoid predators, and communicate, among other things. Jellies put on some of the best light shows in the sea, but they do not do it to look pretty. They rely on bioluminescence to survive, just as we rely on the light of the sun.