The sun shines and warms our body. The energy is carried through the vast space between the sun and the earth by radiation. Unlike conduction and convection, radiation does not need a medium to transfer energy; the energy is carried by electromagnetic (EM) waves. Light is a kind of EM waves that is visible to naked eyes.

Radiation is the process of heat transfer by electromagnetic waves.

A hot object gives out energy by radiation in the form of EM waves. Objects on fire give out visible light because of their high temperatures. Objects at normal temperature range give out mainly infrared radiation that is detected by our skin as warmth. Place your hand near the side, but without touching, a glass of hot water and you will feel what I mean. If the emitted radiation is absorbed by a colder object, the colder object will gain internal energy and rise in temperature.