There is growing evidence for monochromatic blue light effects. However, the role of individual differences in it has not yet been explored. The aim of this experiment was to examine whether chronotype could moderate the monochromatic blue light effect on electroencephalographic (EEG) activity with regard to the timing of exposure. The participants were 30 young male volunteers. A within-subjects counterbalanced design was applied. There were two light conditions comparable in luminance: Monochromatic blue light of 460 nm and polychromatic white light of 6.5 lux. EEG measurements were taken after 4 hours of exposure in the morning, afternoon, and evening. EEG spectral power was categorized into five frequency ranges: delta, theta, alpha1, alpha2, and beta. Chronotypes were assessed by the Morningness-Eveningness Questionnaire. A mixed analysis of variance was applied. Significant interactions between chronotype, light conditions, and the time of the day were found in theta and alpha1 bands after exposure to monochromatic blue light. These preliminary results indicated that in morning-oriented types the spectral power of theta and alpha1 EEG bands was higher in monochromatic blue light when compared to polychromatic white light in the afternoon hours than in the morning or the evening hours. These results may indicate a decrease in alertness in monochromatic blue light in the afternoon hours in morning-oriented types. This could point to the moderating role of individual differences in the monochromatic blue light effect.
Origin, structure, and role of background EEG activity. Part 1. Analytic amplitude