Energy that comes from electromagnetic waves is called radiant energy. Electromagnetic waves take many forms, from microwaves to X-rays to visible light. Radiant energy is, like most forms of energy, measured in joules and is calculated by integrating the radiant flux (power) of the electromagnetic wave with respect to time.
There are two different views of how electromagnetic waves carry energy, and both are considered accurate because of the wave-particle duality concept of quantum theory. Wave-particle duality states that electromagnetic waves act both as physical particles, photons, and as oscillating waves. Radiant energy can be viewed as the energy stored in the photons. It can also be seen as the energy carried in the oscillating magnetic and electrical field produced by the wave-like motion of the electromagnetic wave.
Radiant energy is important to experiments and tasks relating to open systems. In most sciences, an open system is any system that openly exchanges energy with its external environment. Solar energy involves an open system, as the sun's electromagnetic rays are part of the environment while the solar energy collectors and the devices they power are a part of the system. Such energy is also used in photosynthesis as the waves are absorbed by chloroplasts in the cells.
People have devised many uses for radiant energy, which exists in great abundance. The energy from the sun is used to power a wide variety of devices. Radiant heating is another common use of this type of energy. The heat energy is released from walls, ceilings, or other surfaces and is used to heat the objects in the area of the waves directly rather than simply heating the surrounding air, as a fire would do. Such energy can also be used medically in the treatment of some muscular problems.
Nikola Tesla was a pioneer in the study of radiant energy. While some of his theories and ideas were eventually shown to be absurd, others paved the way for many technologies that are now widely-used. He invented one of the first wireless phones to be based on this form of energy. The phone utilized transmitters and receivers that could be turned to the same frequencies to facilitate communication.
Radiant energy is a very abundant resource on Earth. All electromagnetic waves contain such energy. It is easily and commonly generated artificially, and it exists in massive amounts in the natural environment. As scientists learn how to better use the power of electromagnetic waves, the uses for their energy will surely increase in effectiveness and number.