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A recent study by researchers from Basel University and Munich Technical University challenges prior beliefs about the influence of different light colours on the human body’s internal clock and sleep-wake rhythm. Unlike a previous study conducted on mice, this one suggests,
that light colour may be less critical for the internal clock than originally thought.
Vision involves a complex process of perceiving various light wavelengths as colours and brightness in the brain. Photoreceptors in the retina convert light into electrical impulses, transmitted to ganglion cells in the retina and to the visual cortex in the brain. Specialised ganglion cells play a significant role in the internal clock, being sensitive to short-wavelength light at around 490 nanometers, perceived as blue. When activated by short-wavelength light, these cells signal “it’s daytime” to the internal clock.
To explore the influence of light colour on the internal clock, the researchers exposed 16 healthy volunteers to blueish or yellowish light stimuli for one hour in late evening with a white light stimulus as a control condition. The light stimuli were designed to selectively activate the colour-sensitive cones in the retina, while maintaining consistent stimulation of the light-sensitive ganglion cells in all conditions. This allowed the researchers to directly check effects of light on the respective cone stimulation and, the colour of the light.
Contrary to the findings in mice, the study suggests that the colour of light, as encoded by the cones, may not significantly influence the human internal clock and sleep-wake rhythm. The current research contradicts the earlier finding that yellowish light had a stronger influence on the internal clock than blueish light. The results, published in “Nature Human Behaviour”, imply that while light intensity and exposure duration remain crucial factors, the colour of light may not play as significant a role in influencing sleep and circadian rhythms as previously believed.