The effects of red and blue light on alertness and mood at night

This study was designed to explore the roles that long- and short-wavelength lights have on momentary mood and alertness at night. Twenty-two subjects participated in a mixed-design experiment, where we measured the impact of two levels of long- and short-wavelength lights on brain activity and on self-assessments of alertness, sleepiness and mood. Measurements were obtained 60 minutes prior to, during and after light exposure. Results showed that the red and the blue lights increased electroencephalographic beta power (12-30 Hz), reduced sleepiness, and increased positive affect relative to the previous dim-light period indicating that alertness and mood can be affected by light without necessarily stimulating the melatonin pathway. The impact of light was modest, however, compared to the increase in fatigue over the course of the night.