 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.