The human body glows, just too faint to see

Researchers at Tohoku Institute of Technology used an extremely sensitive camera, built to count individual photons, to check whether the human body gives off light too faint for the eye to register.

Masaki Kobayashi's team imaged five volunteers in complete darkness every three hours from 10 a.m. to 10 p.m. and found the whole body glowing continuously, at an intensity about a thousand times below what the naked eye can detect. The glow rose and fell in a daily rhythm, dimmest in the morning around 10 a.m. and brightest in the late afternoon.

The light is a byproduct of ordinary metabolism, generated when reactive molecules produced during cell activity settle back to a lower energy state, and the face, especially the cheeks, glowed more brightly than the rest of the body. Because the signal is so faint, capturing it requires specialized cooled cameras, which has kept the finding mostly confined to physics and imaging labs rather than clinical use.

The human body gives off light too dim to notice.