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Short Blue Light Pulses (30 Min.) in the Morning are Able to Phase Advance the Rhythm of Melatonin in a Home Setting

Geerdink M, Beersma DGM, Hommes V and Gordijn MCM

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 (