Radiator colour again

[john91]

Answers to a previous question agree that black is the best colour for a radiator, but what if the room is in darkness, no lights or windows, is it the same, if so how does the radiator know what colour it is?
John.

[kyoku]

The general agreement is that black as a colour is the best absorber/emitter of energy if we cover the whole electromagnetic spectrum.
A household radiator is designed to heat the house, not to be heated by the room.
If someone paints that radiator black then the radiator does not know anything about the room. The black paint though becomes a good transmitter of the energy of the radiator to that room

[wacky racer]

You can calculate radiated heat by mutiplying the emissivity of the surface by its abolute temperature to the power of four. The closer to black the surface is, the higher its emissivity becomes. For a perfect black body the emissivity is ONE. Black also has the highest absorption coefficient. There is no doubt therefore that black would be the best "radiator" of heat. However in a living room the "radiator" is badly named. It is actually most effective as a convector heater (it heats the air in contact with it). Radiation is only a secondary effect (how close do you need to be to actually feel the radiation?

[knobbynonuts]

very very sad