Light spectra, an imperative zeitgeber, may differ in its chronobiological effects among chronotype ensuing differences in circadian pacesetting. With the increasing usage of colored lights in the environment, the effects of light wavelength on the electrical activity of the brain among chronotypes need to be investigated. Healthy participants (N=24) were recruited to morning, intermediate, and evening chronotype groups using the composite scale for morningness scores. They were exposed to randomized brief sessions of red, green, blue, and white light preceded by 15 min of darkness. EEG was recorded in all sessions. The power spectrum was estimated for alpha, beta, theta, and delta waves from different regions of the scalp and compared among the groups. The morning and evening chronotype had statistically significantly higher mean delta power than intermediate chronotype in colored light. Evening chronotype showed a statistically significantly higher mean beta power than the intermediate chronotype (p=0.013) in green light. Intermediate chronotype had statistically significantly higher mean alpha power than morning (p=0.029) and evening chronotype (p=0.009) in red light. The results show a significant effect of the spectral property of light on brain waves in chronotypes. The green light is more effective in alerting evening chronotypes. The finding of the present study may be applicable in research pertinent to brain imaging in chronotypes especially with red, green, and blue light exposure and chromotherapy-based interventions in affective and psychiatric conditions. Key words Circadian rhythm " Color of light " Light and chronotype " Wavelength of light " EEG in chronotypes.

Department of Physiology All India Institute of Medical Sciences Jodhpur Rajasthan India or

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