Fig. 1

Study protocol. The subjects were admitted to the laboratory 5.5 h before their habitual bedtime. Under dim light condition (2 lux), electrodes and sensors of polysomnographic recording were attached, and dinner was served 5 h before habitual bedtime. Subjects entered into the metabolic chamber and remained in a sitting upright position until bedtime. Following 2 h of dark adaptation (0 lux), subjects were either exposed to blue light LEDs or remained in the no light condition for a subsequent 2 h period. After 8 h of sleep, the basal metabolic rate was measured for 30 min in a supine position, followed by breakfast, and the subjects stayed in the chamber under fluorescent light (270 lux) until noon