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It is known that light in the morning is able to induce phase advances of the endogenous clock, however most studies have tested the phase advances in highly controlled laboratory conditions. At home the environmental lighting is more variable. In theory, a high intensity short morning-light pulse in the short-wavelengths-range (blue light) should be capable of inducing phase advances. If this is also true in a home setting, this could be a firm basis supporting light treatment in late chronotypes who suffer from a late sleep phase. In a study carried out in summer, 11 normal to relatively late (habitual midsleep 4:15-6:09 hours) chronotypes (age range 23-27 years, 4f/7m) participated in two conditions: (1) 1 baseline day followed by 3 consecutive days of 30 min. blue morning-light pulses, (2) 1 baseline day followed by 3 consecutive days of 60 min. blue light pulses. Blue light was applied by use of the Philips GoLite BLU (HF3320, blue leds, intensity at the cornea 2306 melanopic-lux, 300 lux, 3.65 W/m2). During all four evenings, subjects were asked to protect themselves from light exposure (<10 lux). The response of the melatonin rhythm, calculated as a shift in dim light melatonin onset (DLMO), to a single 30 min. light pulse varied between subjects and resulted in a non-significant phase advance of 15 (±48) min. (t10 = 1.04; P = 0.33), and a significant advance of 30 (±41) min. to a single 60 min. light pulse. (t10 = 2.40; P < 0.05). After 3 days of light exposure both in the 30- and in the 60 min. light pulses condition significant phase advances of DLMO were observed; 49 (±58) min. (t10 = 2.80; P < 0.05) and 59 (±29) min. (t10 = 6.9; P < 0.001) respectively. No significant differences were found in the DLMO shifts between conditions. In addition there was a trend for a lower sleepiness score directly after waking up after using light for 3 days in both conditions (t10 = 3.38; P = 0.096, 60 min. and (t10 = 4.10; P = 0.070, 30 min.). A prelimin.ary analysis of actimetry data indicated some support for an effect on sleep timin.g. The data support the conclusion that light pulses of 30 min. in the morning on three consecutive days, in a home setting, in combination with dim light during the evenings, can be part of an efficient phase advancing chronotherapy protocol.