Using cameras so sensitive that they can detect single photons, researchers at Kyoto University discovered that humans emit visible light.
We know, these images look like standard infrared heat maps, but they're not. They actually depict visible light emanating from skin, the results of scientists tracking five 20 year old males standing in front of a dark room camera for frequent sessions throughout a day.
Apparently linked to metabolism, light emittance seemed to rise and fall during the day with the lowpoint tracked to around 10am and the high point around 4pm. Also notable was that the face seemed to consistently emit the most light, a supposed byproduct of more melanin in the skin (the stuff that makes you tanner) because melanin has fluorescent components that might be enhancing the results.