In Radiation heat transfer, no particles are involved to transfer the energy unlike conduction and convection. This means that the energy transfer by radiation work when objects are not touching even in the space
1. We are wormed by sun, even though it is millions of kilometers away is the space.
2. Infrared camera give images even in dark, because they are detecting infrared light not the visible light.
Conduction and convection along with radiation...for radiation see the theory of photo electric effect and Compton effect...
or convection, but it isn't required in order to move heat by radiation.