Radiation is defined as the 'continual emission of infrared waves from the surface of all bodies. transmitted without the aid of a medium'. This simply means that it does not require a medium for energy transfer. Radiation occurs everywhere- from the Sun's rays to vaccuum flasks.
However, there are certain factors that affect radiation- the amout of it and the it's rate.
Colour & Texture of a surface.
Dull black surfaces absorb heat faster and hence are better for radiation than shiny, bright surfaces are. This also means that they emit heat faster and hence are better emitters of infrared radiation.
Surface Temperature
Surface area is the amount of material exposed. If the material has more exposure and two objects that have the same mass, same colour but one has more surface area exposed it will be the one that absorbs/emits infrared radiation better.
Common Applications for Radiation
Greenhouses are used in cold climates to help vegetation grow. This works by it trapping heat. Inside the greenhouse, the grow warm and it emits infrared radiaton.
Teapots are also good applications of radiation. As tea is supposed to be drunk warm, the shiny, bright surfaces of the teapots keep the tea warm for longer as infrared radiation will not be emitted. This concept works two ways- as they are poor absorbers of infrared radiation cold tea stays cold and does not become room temperature.
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