The light-adapted bacteriorhodopsin (BR) photocycle was studied using time-resolved absorption spectroscopy, measuring at 15 wavelengths (380-700 nm), over five decades of time (1 mus to 0.3 s), over a temperature range of 5-35 degreesC, under four solvent conditions (pH 5, pH 7, pH S, and pD 7), and under three polarization conditions (magic angle, parallel, and perpendicular). A spectrotemporal method was developed for simultaneous analysis of these data based upon species-associated spectra (SAS) and fraction cycling. Using mild spectral assumptions, the data were satisfactorily described by a fully reversible scheme with five spectrally different intermediates, and a reversible M-1 reversible arrow M-2 spectrally silent transition, K reversible arrow L reversible arrow M-1 reversible arrow M-2 reversible arrow N reversible arrow O --> BR. The estimated SAS were realistic. The free energy gradually decreased between the K and N or O intermediate by 10-20 kJ/mol. An alternative kinetic scheme containing an M-1 reversible arrow M-2 transition that becomes unidirectional above pH 6 (Ludmann et al., Biophys: J. 1998, 75, 3110-3119) did not fit these data well. At all temperatures, the L to M transition was strongly retarded upon deuteration indicating strong involvement of proton translocation during this step. The polarization model analysis showed a reduced anisotropy of the M-2 intermediate, indicating retinal reorientation.