Light-at-night (LAN) has become a defining feature of human and animal ecosystems and may possibly compromise human and animal physiology and health. Spectral and acclimation duration (AD) sensitivity were compared between social voles (Microtus socialis) and 'blind' mole rats (Spalax ehrenbergi) in four increasing ADs (0, 1, 7 and 21 days) to LAN (1×30 min, 293 μW cm(-2)) of three different monochromatic lights [blue (479 nm), yellow (586 nm) and red (697 nm)]. Animals were sampled for urine and oxygen consumption (V(O(2))) promptly after each LAN-AD. Urine samples were analyzed for production rate, urinary 6-sulfatoxymelatonin and urinary metabolites of adrenalin and cortisol. Overall, the blue light elicited the greatest effects on the biological markers of M. socialis, whereas similar effects were detected for S. ehrenbergi in response to red light. The increasing LAN-AD resulted in a dose-dependent decrement of all markers tested, except of stress hormones, which showed a direct positive correlation with LAN-AD. Our results suggest that: (1) photoperiod is an important cue for entraining physiological functions in the 'blind' S. ehrenbergi, which is essentially characterized by red-shifted sensitivity compared with the blue-shifted sensitivity detected for the sighted counterpart species, and (2) there is a strong association between LAN of the appropriate wavelength and adrenal endocrine responses, suggesting that LAN is a potential environmental stressor.