In a randomized, cross-over design, 16 subjects with recurrent autumn-winter symptoms but without major depression were treated with 4 days of dawn simulation consisting of a gradually increasing illuminance over 45 min peaking at 100 lx (slow dawn) and with 4 days of a light rapidly increasing over a 4 s period to 100 lx (rapid dawn). The slow dawn was significantly better than both baseline and the rapid dawn in improving subjective measures of energy, mood, social interest, productivity, quality of sleep and quality of awakening.