 Radiant energy is usually carried by the electromagnetic radiation. The S.I. unit of radiant energy is the joule (J) just as is the case with the rest of the forms of energy. The electromagnetic radiation is in form of waves referred to as electromagnetic waves.

Radiant energy is a form of energy that is capable of travelling through space. An example of the radiant energy is the solar heat (heat from the sun) that we receive daily. The sun is millions of miles away from the earth and the space between the two is essentially a vacuum. However the radiant energy from the sun travels through this vacuum to reach earth in the form of EM waves.

The electromagnetic radiation can also be visualized as a series of photons in motion. Therefore, radiant energy is the energy carried by these photons. At the same time, as mentioned earlier, the electromagnetic radiation is an electromagnetic wave which carries energy in its fields. The fields of the electromagnetic waves include the electric fields and the magnetic fields that oscillate.

The electromagnetic radiations can have differing frequencies. The energy possessed by each of the photons is proportional to the frequency at which the photon is travelling at. For example, there is a proportionality between the energy of a monochromatic wave and the intensity of the wave; which infers that with two electromagnetic waves having similar intensity, but dissimilar frequencies, the electromagnetic wave with the higher frequency has a smaller quantity of photons. This concept is taught during our H2 Physics tuition classes on Quantum Physics.

The energy of the electromagnetic waves can be transformed to heat when an electromagnetic waves are absorbed by an object. This is the case with the energy from the sun as it tends to warms the surfaces that it illuminates. The energy of the electromagnetic waves can also be transformed to electricity in the case where the object absorbing the waves contains a photoelectric material. Electromagnetic waves also obey the laws of reflection and refraction.