It is only the warming rays of the sun that make it possible for the phenomena we call life to exist here. Without light, and the energy it carries, our planet would be a dead as all the rest of the planets in our solar system. Light is important to us because of the power it brings. Humans, and many other animals, also use light in another way. Over millions of years, creatures as diverse as shellfish and humans have evolved special sensors that can detect and interpret rays of light.
Animals move in search of food, habitat, mates and to avoid predators.
Long range sensors such as eyes make these tasks much easier and more sure. The ability to collect and focus light onto a biologically sensitive surface, and then interpret the signals received has been a critical one in animal evolution. Our eyes can only detect objects above a certain size. For thousands of years, therefore, humans were unaware of the vast world of organisms that exist below the resolving power of our eyes. It was not until humans discovered the properties of light, what it is and how it can be manipulated, that they began to discover and investigate the world of cells.