There is the photobiomodulation (PBM) of laser irradiation or monochromatic light (LI) on biosystems. The quantum mechanics of the interaction of LI and cellular molecules determines PBM dosage. The PBM of low intensity LI, -10 mW/cm², is mainly mediated by state-dependent extraocular phototransduction, but the PBM of moderate intensity LI, 10²-10³ mW/cm², is mainly mediated by reactive oxygen species mediated signal transduction, both of which support our biological information model of PBM (BIMP). The signal transduction pathways can be classified as two kinds, pathway 1 mediated by the Gs protein mediated pathways, and pathway 2 mediated by the other pathways such as protein kinase Cs mediated pathways and mitogen-activated protein kinase mediated pathways. Almost all the present pathways found to mediate PBM belong to pathway 2, but pathway 1 mediated PBM has been predicted according to BIMP.