Light, the form of radiant energy that makes vision possible. Since sight is the most important of the senses, light furnishes most of the information we have about our surroundings. Even more important, light makes life possible. In the process called photosynthesis, plants and some other organisms use the energy of sunlight to make food from water and carbon dioxide. Animals obtain their food by eating such organisms or by eating animals that eat such organisms. The energy of sunlight contained in an animal's food is released when the food is oxidized (combined with oxygen) in the animal's body. Thus most living things receive their energy, directly or indirectly, from light.
The energy of sunlight is also stored chemically in wood, coal, petroleum and other fuels that are the remains of plants and animals. When these fuels are burned (rapidly combined with oxygen), part of this energy is given off as heat, and part as light.
Light influences living things in many other ways. Plants and some primitive animals move either toward or away from light. Most flowering plants open their flowers in response to light. Flowers typically bloom only when the hours of daylight are a certain length. The response of living things to the hours of daylight is called photoperiodism. Among other things, photoperiodism determines when plants prepare to shed their leaves, and when certain animals breed, hibernate, or migrate.
Light produces electricity in some substances, such as those used in solar batteries. In such materials as photographic films and papers, light produces chemical changes.
