ABSTRACT
Energy is absorbed, reflected, and radiated by all plants and animals and most animals use some of the information carried by radiant energy to modify their subsequent behavior. Electromagnetic radiation can be thought of as little packages of energy, each package being a discrete unit. The amount of energy in a package characterizes the type of radiation. Energy/package is only one way to characterize electromagnetic radiation. Under some experimental conditions, electromagnetic radiation acts like a stream of particles; under other conditions radiation acts like waves. High-energy radiation acts as though its waves were very close together, with a high repetition rate, or frequency, and a very short distance between adjacent wave crests. Interestingly, visible light displays a good mix of wave and particle properties, given the scale and sensitivity of usual measuring devices. In addition to absorption, particles in the atmosphere also scatter sunlight.
