That's a good question. All bodies above the temperature of absolute zero emit electromagnetic radiation across the whole spectrum (this is called Black-body ra

That's a good question. All bodies above the temperature of absolute zero emit electromagnetic radiation across the whole spectrum (this is called Black-body radiation). Think of it as a mixture of different amounts of light of every possible wavelength. However, what the exact mixture is depends on the temperature of the body. As the body gets hotter, the 'peak' wavelength, i.e. the wavelength whose "amount" is highest in the mixture decreases. Objects at room temperature emit most of their energy outside of the visible spectrum, so they are not 'visible' in the dark. However, as you heat them up, the radiation mixture moves towards lower wavelengths, closer to infra-red. Heat it up further and things become red hot, yellow, blue hot and so on. Infra-red LEDs produce light of the the specific infrared wavelength through semi-conductors. They have nothing to do with the black-body radiation one associates with 'hot' objects.