Steady-state fluorescence measurements of the first excited state of the anabaena sensory rhodopsin (ASR), and Bacteriorhodopsin are reported for different light stabilization conditions, including the dark-adapted state. We determine the fluorescence spectra of both all-trans (AT), and 13-cis (13C) protonated Schiff base of retinal, and compare the effect of the proteins. Referenced against the fluorescence quantum yield of AT-bR (2.5 x 10(-4)) we find for AT-ASR, 13C-ASR, and 13C-bR the values of 3.3 x 10(-4), 0.8 x 10(-4), and 1.7 x 10(-4), respectively. Using reported excited state lifetimes, the radiative rates are deduced, and their differences discussed on the basis of a configuration-dependent oscillator strength. (C) 2013 Elsevier B. V. All rights reserved.