|MadSci Network: Biochemistry|
The reference in the song is probably interpreting Einstein's BIG IDEA that E=mc2. In other words Energy is directly related to matter. So in a sense we are made of light. As to light being emitted by the body, the short answer is no. We can emit light if we burn or if we are infected by certain bacteria.
Phosphorescent chemicals are not uncommonly produced by microorganisms, including "household germs" like Escherichia coli, Staphylococcus aureus, Bacterium phosphoreum and Bacillus subtilis. A particularly common class of phosphorescent biological products of these micro-organisms covers the zinc-porphyrins, which are structurally related to haem molecules in haemoglobin. These have been found to be responsible for the "afterglow" in decaying milk, serum and urine. You can also find light emitting bacteria around toilets and urinals that use seawater.
[Moderator's note: While the human body does not emit visible light, it does emit non-visible radiation, as described in this answer from our archives (926874398.Gb).]
Try the links in the MadSci Library for more information on Biochemistry.