Vision is a complex process that relies on converting different wavelengths of light into electrical impulses that are deciphered in the brain as color and brightness.
Photoreceptors in the retina, known as cones, facilitate clear, detailed, colored vision in sufficient light.
Rods, on the other hand, contribute to vision in low light, allowing us to distinguish between different shades of gray, but with less precision.
The electrical impulses are then transmitted to ganglion cells in the retina, where they are further processed in the visual cortex of the brain, resulting in the perception of color images.
Color of light and its effect on sleep
It's important to note that ambient light not only allows us to see, but also affects our sleep cycles and circadian rhythms.
Specialized ganglion cells, such as cones and rods, are sensitive to light and respond strongly to light at short wavelengths of about 490 nanometers.
When we are exposed to light that consists only of short wavelengths between 440 and 490 nanometers, we perceive it as blue.
When this light activates ganglion cells, it signals the body's internal clock that it is daytime. Rather than the perceived color, the intensity of the light at each wavelength is the determining factor.
Rods, cones, and color
Dr. Christine Bloom of the Chronobiology Center University of BaselResearching the effects of light on humans, he raises the question of whether cones, and by extension the color of light, also affect our biological clocks.
“Light-sensitive ganglion cells also receive information from cones. This raises the question whether cones, and by extension the color of light, also influence our internal clocks,” explains Dr Bloom. do.
“After all, the most noticeable changes in brightness and light color occur at the moments of sunrise and sunset, which mark the beginning and end of the day,” says Blume.
A 2019 study on mice suggested that yellowish light has a stronger effect on the body's internal clock than blueish light. However, the main effects of light on human circadian clocks and sleep are likely mediated through light-sensitive ganglion cells.
Dr. Bloom adds, “There is reason to believe that the color of light encoded by cones may be related to our biological clock.”
Studying the effects of light color
To uncover the truth behind these hypotheses, the research team exposed 16 healthy volunteers to a bluish or yellowish light stimulus for an hour late at night. White light stimulation was included as a control condition.
Light stimulation was carefully designed to differentially activate color-sensitive cones in the retina, while stimulation of light-sensitive ganglion cells remained consistent across all three conditions. This allowed the researchers to isolate the specific effects of color on body clocks and sleep.
“This light stimulation method allows us to isolate in a clean experimental way the properties of light that may play a role in how light affects humans,” said the university's Time said Manuel Spitchan, professor of biology and health. Munich University of Technologyhe also participated in the study.
In the sleep lab, researchers assessed whether the color of light affected participants' internal body clocks.
They also assessed the time it took the volunteers to fall asleep, the depth of their sleep at the beginning of the night, their reported fatigue, and their ability to react, which naturally decreased as they became sleepier.
Research results on light color, sleep, and body clock
The findings show that changes in the color of light along the blue and yellow dimensions do not play a role related to human body clocks or sleep. This contradicts the results of the mouse studies mentioned above.
“We found no evidence that changes in the color of light along the blue and yellow dimensions play a role related to human body clocks or sleep,” Dr Bloom says.
“Rather, our results confirm the findings of many other studies that light-sensitive ganglion cells are most important for the human circadian clock,” say the scientists.
Manuel Spitchan believes that this research will contribute to bridging the gap between basic research and practical application.
He said: “Our findings show that when planning and designing lighting, it is perhaps most important to consider the effects of light on light-sensitive ganglion cells. Cones, and therefore color, are highly play a subordinate role.”
The influence of “blue light” and future research
It remains to be investigated whether light color does not affect sleep even when parameters are changed, such as longer light exposure or changing time frames. Follow-up studies are needed to address these questions and gain further insight into the relationship between light color, body clock, and sleep.
Experts frequently advise that short-wavelength “blue light” emitted by smartphones and tablets disrupts our biological rhythms and sleep patterns.
Therefore, it is recommended to use these devices early in the evening or enable night shift mode, which reduces short wavelength light and gives it a yellowish tint.
However, Dr. Bloom points out that this yellowish adjustment is an unnecessary byproduct. “Technically, it is possible to reduce the short wavelength light in these displays without changing the color, but commercially available mobile phones have not yet adopted this approach,” she explains.
In summary, this study dispels myths about the influence of light color on human body clocks and sleep. Although light-sensitive ganglion cells play an important role, the color of light encoded by cones is less important.
As future research delves deeper into this topic, we will recognize the pivotal role of light-sensitive ganglion cells in designing lighting solutions that promote healthy sleep patterns and support overall well-being. That becomes important.
The entire study was published in the journal nature human behavior.
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