You might be interested in biophotons: human body emits dim light constantly. These photons may be functional and not just a byproduct. Many sources are a bit '

You might be interested in biophotons: human body emits dim light constantly. These photons may be functional and not just a byproduct. Many sources are a bit 'woo', so take with a grain of salt, but there is an idea floating around that some molecules are excited by specific wavelengths, and so by targeting cells with these wavelengths you can preferentially change the reaction rate of certain molecules it contains.