The effect of polarized versus nonpolarized light on melatonin regulation in humans

The aim of this study was to compare the effects of polarized light versus nonpolarized light on melatonin secretion in healthy, humans (mean age, 25 years; N = 6). On separate evenings, each subject was exposed to four diffe rent light intensities (20, 40, 80 and 3200 Ix) of both polarized and nonpo larized light, as well as to a control, dark exposure. Each evening experim ent consisted of a 120 min dark exposure (0000-0200 h) followed by a 90 min light exposure (0200-0330 h). Subjects' pupils were dilated prior to expos ures. Blood samples were drawn at the start and end of each light-exposure period and later assayed for melatonin by radioimmunoassay. When compared t o control exposures, both polarized and nonpolarized light elicited signifi cant suppression of plasma melatonin at each illuminance (P < 0.03 to P < 0 .0001), There were no significant differences between the effects of polari zed light and nonpolarized light at any illuminance. The two light stimuli modalities demonstrated very similar fluence-response relationships between illuminance and melatonin suppression. Thus, the human pineal gland is res ponsive to ocular exposure with polarized light in a dose-dependent manner similar to that of nonpolarized light, although no significant differences were detected between polarized and nonpolarized light on melatonin regulat ion.