Black-body Radiation
You glow, but not a lot. It is possible to build infrared detectors to photograph your glow but it can not be done with film, because the film would go black in the camera by itself. The usual way is to build semiconductor arrays which work better if cooled with liquid air. Enhancing a raw low contrast image with special Adobe-type software gives quite remarkable results.
Click to enhance
Black-body Radiation Black-bodies are not exactly black. They can be bright like the Sun ... it all depends on how much hotter they are than the surroundings.
A black-body is both an ideal absorber and an ideal radiator of energy. The ones I like best are the Thai clay-ball fireworks. Look inside when the sparks have finished roaring out the hole. The cavity is coated inside with a fresh layer of soot. If light or heat waves go in the hole they bounce around inside and get absorbed. The orange glow you see is the reverse. The walls of the cavity emit radiation which is absorbed and reradiated until some escapes out the little hole.
Black-body radiation has a particular continuous spectrum. The Graph shows intensity versus wavelength. The curve can be scaled for intensity to fit any size of source and scaled for wavelength to fit a source of any temperature.
The peak for sunlight is in the visible region (it has to be!). There is a 'cut off' in the UV and a long upper tail in the infrared. The peak wavelength is given by a simple formula known as Wein's law.
The peak of the solar output is at 4.8 nm in the green. Persons are not so hot. At a little over 300 K the peak is in the infrared.
The military had been taking thermal photographs for years in the late 20th century before the equipment slowly got in to the consumer market. Sony had [in 2000] a digital camera that worked just fine at room temperature but the results were a little too revealing, and they had to pull it.
Question: persons are not so hot. What about really cold things? If we could detect the heat radiation from a bowl of liquid helium at 4 K where would the peak be?
The question is a good one with an answer. The tiny amount of radiation coming from our bowl of liquid helium peaks in the microwave region! That is not so bad because microwaves are not that hard to detect - the TV and telephone people do it all the time.
Example 1 .............. color temperatures
Example 2 .............. an IR digital camera
Example 3 .............. an optical pyrometer
