What do you think of this fact?
Fireflies, deep-sea fish, glowing mushrooms: when you hear “bioluminescence,” you think of exotic creatures. But you glow too. Right now. Just so faintly that your own eyes don’t stand a chance.
A camera that sees almost nothing, and still enough
In 2009, Japanese researchers Masaki Kobayashi, Daisuke Kikuchi and Hitoshi Okamura published a study in the journal PLOS ONE. They put five healthy men in their 20s in front of an extremely sensitive CCD camera cooled to minus 120 degrees Celsius. The result: the human body gives off light, but about 1000 times weaker than what our eyes can detect.
The face was the brightest part, especially the cheeks and the area around the mouth. The eye area and the rest of the body glowed less.
Your glow runs on a schedule
The researchers filmed their volunteers at different times of day, and the glow wasn’t constant. It was weak in the morning, grew stronger over the day and peaked in the late afternoon, around 4 p.m. At that point, the cheeks were about twice as bright as at 10 a.m.
Here’s the interesting part: the glow moved in the opposite direction to the stress hormone cortisol. So the researchers suspect that your body clock, through your metabolism, helps set how brightly you shine.
Where the light comes from
The source isn’t a special light organ like a firefly’s. It’s plain old metabolism. Your cells produce free radicals, highly reactive molecules. Their chemical reactions briefly push some molecules into an excited state. When those molecules drop back down, they release the extra energy as a tiny particle of light, a photon.
Scientists call this ultraweak photon emission. It isn’t unique to humans, either. Lots of living things do it.
According to Wikipedia, tissues give off roughly 1 to 1000 photons per square centimeter per second. A desk lamp blasts out unimaginably more.
So no, you’re not a light bulb. But there’s a little light in you, and the most of it shows up around 4 in the afternoon.