Past research has shown that the body emits visible light, 1,000 times less intense than the levels which can be seen with the naked eye. In fact, virtually all living creatures emit very weak light.
To learn more about this faint visible light, scientists in Japan employed extraordinarily sensitive cameras capable of detecting single photons. Five healthy male volunteers in their 20’s were placed bare-chested in front of the cameras in complete darkness in light-tight rooms for 20 minutes every three hours.
The researchers found the body glow rose and fell over the day, with its lowest point at 10 AM and its peak at 4 PM, dropping gradually after that. These findings suggest there is light emission linked to the body clock, most likely due to how metabolic rhythms fluctuate over the course of the day.
Faces glowed more than the rest of the body. This might be because faces are more tanned than the rest of the body, since they get more exposure to sunlight.
PLoS One July 16, 2009; 4(7): e6256 [Free Full-Text Article]