Screen light in the evening – problems falling asleep: does blue light really wake you up? – Knowledge
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A recent study shows that it is not the high blue content of LED light from a screen that prevents us from falling asleep.
A well-known rule for good sleep is: no cell phone time before bed. The type of light that hits our eyes influences our sleep-wake rhythm. The screen light from smartphones and other technical devices is similar to that which we see during the day.
Accordingly, our brain interprets the LED light as a day signal. Many studies show that this inhibits the production of melatonin – the hormone that makes us feel tired. Not exactly practical when we want to fall asleep.
Tips for a restful night
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Legend:
Christine Blume, sleep researcher and therapist
NaWik, Annette Mueck
In addition to research, Christine Blume works as a sleep therapist at the University Psychiatric Clinics in Basel. She recommends setting the smartphone to night mode, but emphasizes: “What we do on the smartphone before going to bed probably has a greater impact than the LED light.” It holds our attention and is entertaining. And: “When we scroll, 15 to 20 minutes or more can quickly go by without us noticing it. We don’t have that time to sleep,” says Blume. She gives two simple rules for those who have trouble falling asleep:
Do not lie awake in bed for more than 20 minutes If you can’t fall asleep in bed for what feels like 20 minutes (because constantly looking at the clock adds stress), you should get up again and keep yourself busy, for example reading a book. And only slip under the covers again when you’re really tired. “This prevents you from nodding off and waking up again,” explains Blume. People with sleep disorders often have the impression that they never slept – even though they did. Another advantage of this method: It may take a long time to fall asleep. The next day you are particularly tired and therefore fall asleep more easily in the evening.
Help against the carousel of thoughts – a look into the roof of the sky “Many patients report that they can hardly get out of their thoughts,” says the therapist. Visualization sometimes helps people who are caught in a carousel of thoughts. «Imagine you are looking at the sky. Large cumulus clouds pass by. And you put every thought on a cloud,” says Blume in a soothing voice.
In this context, it is often said that the high blue content of cell phone light keeps us awake. Appropriately, the function in night mode is also called blue filter. This reduces the short-wave light components and looks slightly yellowish. But: “This colloquial term for ‘blue light’ is somewhat misleading,” says Christine Blume, sleep researcher at the Center for Chronology at the University of Basel.
She and her colleagues recently conducted a study published, which comes to the conclusion: Regardless of whether we receive white, blue or yellow light – our internal clock is most likely not disturbed by the color of light. What is crucial for the “wake-up” effect of light is the high proportion of short wavelengths.
Technologically, it would be possible to reduce the short-wave light component without adjusting the color of the display. However, this has not yet been implemented in commercial cell phone displays
It makes sense to put your cell phone away early in the evening or at least reduce the brightness of the display and activate night mode. Because the short-wave light is filtered out, the color change is just an unnecessary by-product. Blume explains: “Technologically, it would be possible to reduce the short-wave light component without adjusting the color of the display. However, this has not yet been implemented in commercial cell phone displays.”
More about the new sleep study
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Researchers from the University of Basel and the Technical University of Munich exposed 16 healthy volunteers to a light stimulus for an hour late in the evening. In three different conditions: a bluish or a yellowish light stimulus and, for control purposes, a white light. The light exposure was designed to activate the color-sensitive cones in the retina differently. The short wavelength component of the light at around 490 nanometers, however, was the same in all three conditions, which kept the response of the ganglion cells stable. In other words: Differences in the lighting effect were directly due to the respective stimulation of the cones and ultimately to the color of the light.
The researchers then determined whether the participants’ internal clocks had changed depending on the color of the light. Among other things, they recorded how long it took the test subjects to fall asleep, how deeply they slept at the beginning of the night and how high their melatonin levels were. The researchers also asked about their tiredness and tested their ability to react, which decreases as sleepiness increases.
No significant differences between the conditions could be found in the results. The conclusion: The light colors did not have a different effect on the participants’ internal clock and sleep.
What actually happens when light hits our retina and tells our body whether it should stay awake? The so-called ganglion cells are crucial for the process. The specialized receptors convert light stimuli into bioelectrical excitation. They react particularly sensitively to short-wave light of around 490 nanometers.
Sensitivity to light – varies from person to person
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There are Hintsthat people have different sensitivity to light depending on age, gender, chronotype or even genes. For example, younger people tend to absorb short-wave light better than older people. From around the age of 25, the lens of the eye changes increasingly and becomes cloudier. This acts like a filter and means that the internal clock of older people is less disrupted. However, there is also evidence that refutes this assumption. That’s how it comes an investigation concluded that with increasing age, the short-wave LED light penetrates the lens less well, but this does not reduce melatonin production.
When short-wave light activates the ganglion cells, they signal to the internal clock that it is daytime. We perceive this light as blue. And here comes the crux of the matter: If other wavelengths are also contained in the light, the perceived color can change. In other words: white or even yellowish light can also have short-wave components that activate the ganglion cells.
Results from mouse study refuted
The current findings therefore refute this a 2019 study with mice. The authors came to the conclusion that yellow light had a greater influence on the internal clock than blue light.
In our study, we found no evidence that variations in light color play a relevant role in people’s internal clock or sleep.
Christine Blume counters: “In our study, we found no evidence that variations in the color of light along a blue-yellow dimension while maintaining the same activation of the ganglion cells plays a relevant role in people’s internal clock or sleep.”
And she adds: “Our results actually support the results of many other studies that the light-sensitive ganglion cells have the greatest importance for our internal clock.” However, further research is needed to clarify whether the light color has no influence even if the duration of exposure to light is extended.
