Dawn and dusk simulation as a therapeutic intervention

Abstract

Daily alternations of light and darkness entrain circadian rhythms of body tem~rature, rest-activity, and melatonin and other neuroendocrine secretions (cf., Moore-Ede et al. 1982). Annual cycles of changing light-dark patterns underlie seasonal metabolic and behavioral cycles and, in humans living distant from the equator, a syndrome of winter depression with prominent atypical neurovegetative symptoms of fatigue, hypersomnia, carbohydrate craving, and weight gain (Rosenthal et al. 1984). Affected individuals suffer annual cycles of spontaneous relapse and remission, generally in autumn and spring, respectively. Early-morning artificial bright light (>2000 lux) provides effective treatment in this variant of depression (Rosenthal et al. 1985; Lewy and Sack 1986; Terman 1988), while also inducing immediate suppression of n~tumal melatonin secretion (Lewy et al. 1980), and within several days, circadian phase shifts (Lewy et al. 1985; Terman et al. 1988). In humans, normal indoor illumination levels (<800 Iux) have proven