biophoton

Biophotons (from the Greek βίος meaning "life" and φῶς meaning "light") are photons of light in the ultraviolet and visible light range that are produced by a biological system. They are non-thermal in origin, and the emission of biophotons is technically a type of bioluminescence, though the term "bioluminescence" is generally reserved for higher luminance systems (typically with emitted light visible to the naked eye, using biochemical means such as luciferin/luciferase). The term biophoton used in this narrow sense should not be confused with the broader field of biophotonics, which studies the general interaction of light with biological systems.

Biological tissues typically produce an observed radiant emittance in the visible and ultraviolet frequencies ranging from 10−17 to 10−23 W/cm2 (approx 1–1000 photons/cm2/second). This low level of light has a much weaker intensity than the visible light produced by bioluminescence, but biophotons are detectable above the background of thermal radiation that is emitted by tissues at their normal temperature. Biophoton emission is also known as "ultraweak photon emission" (UPE).