[Photoperiod phototherapy and wakefulness-sleep rhythm disorders].

Bright light therapy is a recent physical treatment in chronodisabled situations. The most recognized indication is the seasonal affective disorder. However, any disease or dysfunction where a misalignment of sleep-wake and circadian rhythms may be suspected is a potential tool for this treatment. Analyses of the literature throughout the interpretation methods of the evidence based medicine indicate that bright light therapy, if not a standard, could be recommended in a number of circadian rhythm sleep disorders, mainly the delayed and advanced sleep phase syndromes. Time aspects are essential for the success of phototherapy. From this point of view, easy and practical technological means or methods, allowing to shape a Phase Response Curve in each individual to be treated, should be clear progress. A future extension of indications will also depend on the checking of essential hypotheses linking circadian and sleep-wake rhythms in diseases such as psychophysiological insomnia, multiple sclerosis, brain dysgeneses or dementias. At last, a non negligible advantage of bright light therapy appears to be its relative safety.