Comment by xenadu02

Biophotons (or ultra weak photon emission) has been known about for decades. Various reactive oxidative molecules release light when coming down from an excited state. Some enzymatic activity is also known to produce light.

The big question has been just how much useful information can be derived from that light? It is difficult to tease out signal from noise and the human body is far from transparent at those frequencies so it's not like you could use it for imaging.

Since breathing stops and various oxidation reactions thus also slow or stop it makes sense the emitted light would decrease.