Rainbow, Niagara Falls, New York, 2001 Photograph by Joe McNally/Sygma Rainbows, such as this one produced by artificial light shone on an icy Niagara Falls, are just one special effect of light, a marvel that reveals the world to us. Light sets our biological clocks. It triggers in our brains the sensation of color. Light feeds us, supplying the energy for plants to grow. It gives us life-changing tools, from incandescent bulbs to lasers and fiber optics. Scientists don't fully understand what light is or what it can do. They just know that it will illuminate our future.