Glowing in the dark has always been contributed to people exposed to radiation in cartoons (think Homer Simpson) and in popular myths about nuclear accidents (Chernobyl). Turns out we all glow continuously, but with a diurnal rhythm, as long as we have a powerful enough digital camera to detect the luminescence. A team of Japanese scientists used a light-proof room to detect photon activity coming from the body of five subjects over time, and initial results point to metabolic activity as the mechanism that affects the amount of photons emitted.
From the introduction of the article in PLoS ONE:
Bioluminescence, which is weak but visible, is sometimes produced in living organisms, such as fireflies or jellyfish, as the result of specialized enzymatic reactions that require adenosine triphosphate. However, virtually all living organisms emit extremely weak light, spontaneously without external photoexcitation. This biophoton emission is categorized in different phenomena of light emission from bioluminescence, and is believed to be a by-product of biochemical reactions in which excited molecules are produced from bioenergetic processes that involves active oxygen species. Human body is glimmering with light of intensity weaker than 1/1000 times the sensitivity of naked eyes. By using a sensitive charge-coupled-device (CCD) camera with the ability to detect light at the level of a single photon, we succeeded in imaging the spontaneous photon emission from human bodies.
Previously, for obtaining an image, it took more than 1 hour of acquisition, which is practically impossible for the analysis of physiologically relevant biophoton emission. By improving the CCD camera and lens system, here we have succeeded in obtaining clear images using a short exposure time, comparable with the analysis of physiological phenomena. Since metabolic rates are known to change in a circadian fashion, we investigated the temporal variations of biophoton emission across the day from healthy human body.
Full article in PLoS ONE: Imaging of Ultraweak Spontaneous Photon Emission from Human Body Displaying Diurnal Rhythm
