Absolute darkness does not mean that our body stops emitting light. Human beings release photons continuously, even if their intensity is too low for us to see them. This is not infrared radiation or body heat: we are talking about real visible light, emitted in extraordinarily small quantities.
Researchers in Japan managed to record that glow using ultrasensitive cryogenic cameras. The images made visible to the scientific team something that remains hidden to the naked eye: the emission of biophotons from the body itself. According to the study, this light is about a thousand times weaker than the threshold that the human eye can capture without instrumental help. That’s why we don’t glow noticeably when we enter a dark room.
The origin of these tiny flashes is related to metabolism. When you breathe and obtain energy, reactions occur in the cells. Free radicals can react with proteins and fats, giving rise to excited molecules that release part of their energy in the form of photons when they return to a lower energy state. It is a side effect of normal biological processes, not a source of illumination comparable to a lamp.
The broadcast also does not remain exactly the same at all times. The team observed that it varies throughout the day following a circadian rhythm: it increases until reaching a maximum in the middle of the afternoon and decreases during the early morning, while we sleep. That pattern suggests a relationship with daily changes in metabolism. So the expression “biological light bulb” works as a metaphor: we emit light, yes, but on a scale that only specialized instruments can detect.
Santiago Campillo (@Scruzcampillo) is a biologist and scientific communicator specialized in health, nutrition and nature.
