Light emitting diodes can be used to phase delay the melatonin rhythm

Two portable light sources, comprising light emitting diodes (LEDs) of two different wavelengths, were compared to a standard light box in suppressing and phase shifting nocturnal salivary melatonin. All light sources were eq uated for illuminance of 2000 lux. Sixty-six volunteers participated in the 2-day study and were randomly allocated to one of four conditions; light b ox. white LED, blue/green LED. or no light control group. Light was adminis tered to the experimental groups from midnight to 02.00 hr on the first nig ht. Half-hourly saliva samples were collected from 19.00 to 02.00 hr on nig ht 1 and until 01.00 hr on night 2. Percent melatonin suppression on night 1 and dim light melatonin onset (DLMO) for each night were calculated. The experimental groups showed significant melatonin suppression during light s timulation, with the blue/green LEDs producing the greatest (70%) suppressi on. There was no significant difference between the light box at 63% and wh ite LED at 50% suppression. Similarly, the blue/green LED had a significant ly greater DLMO delay of 42 min and no difference between the light box of 23 min and the white LED of 22 min. These data suggest the portable LED lig ht source is an effective way of delivering light to phase shift the melato nin rhythm, with the blue/green LED being the more effective of the two LED s.