Humans are not alone in emitting a faint glow. This phenomenon has been observed in all living organisms, including humans, and is thought to be caused by a process called ultraweak photon emission. In this process, energy-producing machinery in our cells releases tiny particles of light as molecules gain and lose energy.
Research suggests that this signal can be detected with the right equipment, potentially allowing scientists to track forest health or detect diseases in people. While the idea may seem like science fiction, it is a real possibility being explored by researchers.
Source: https://www.newscientist.com/article/2479590-all-living-things-emit-an-eerie-glow-that-is-snuffed-out-upon-death