A new study has shed new light on the influence of different light colours on the human body's internal clock and sleep-wake rhythm. The study conducted by researchers from the University of Basel and the Technical University of Munich (TUM) contradicts the results of a previous study conducted in mice, suggesting that light color may be less important for the internal clock than originally thought.
Vision is a complex process that involves the perception of different wavelengths of light as colors and brightness in the brain. Photoreceptors in the retina convert light into electrical impulses, which are then transmitted to ganglion cells in the retina and further to the visual cortex in the brain.
In terms of the internal clock, specialised ganglion cells play a significant role. These cells are sensitive to light and react strongly to short-wavelength light at around 490 nanometers, which is perceived as blue When these ganglion cells are activated by short-wavelength light, they signal to the internal clock that it is daytime.
Influence on the internal clock
To explore the influence of light color on the internal clock, the researchers exposed 16 healthy volunteers to blueish or yellowish light stimuli for one hour in the late evening, as well as a white light stimulus as a control condition. The light stimuli were designed to differentially activate the color-sensitive cones in the retina, while the stimulation of the light-sensitive ganglion cells remained the same in all three conditions. This allowed the researchers to directly attribute any differences in the effects of the light to the respective stimulation of the cones and ultimately the color of the light .
The researchers' findings suggest that the colour of light, as encoded by the cones, may not have a significant influence on the internal clock and sleep-wake rhythm in humans . While a previous study in mice suggested that yellowish light had a stronger influence on the internal clock than blueish light, the current study's results contradict this finding. "A study in mice in 2019 suggested that yellowish light has a stronger influence on the internal clock than blueish light," says Christine Blume at the Centre for Chronobiology of the University of Basel.
These findings, published in the scientific journal "Nature Human Behaviour", have important implications for our understanding of the impact of light on sleep and circadian rhythms. While light intensity and exposure duration remain crucial factors, the colour of light may not play as significant a role as previously believed.
