A research group from the University of Manchester, led by Dr. Tim Brown, studied the effects of blue light on the circadian cycle of mice and found that the effects were contrary to those commonly believed. However, there are many points to highlight before throwing stones at the night modes of our smartphones and other filters available here and there.
The blue light problem
Our biological clock uses melanopsin, a light-sensitive protein located in our eye, to measure the ambient light and decide whether, for example, to produce melatonin – also called the sleep hormone. Melanopsin is however more sensitive to shorter wavelength photons, namely blue to green lights.
We deduce that the blue light commonly found in our computer or smartphone screens would disrupt our circadian cycle by tricking our body into believing that the light is still powerful, thus preventing our brain from creating enough melatonin to fall asleep.
This is why we currently find on iOS and Android (but also on Windows and other systems) a “night mode” reducing blue lights and giving a yellow tint to our screens.
A new study says otherwise
However, Dr. Tim Brown's team started from the postulate that natural night light tends more towards bluish colors, while daytime lights tend more towards warm colors, and that it would therefore be more obvious that our cycle is based on these colors. The researchers therefore carried out tests on mice by exposing them to more “yellow” or more “blue” light, without reducing the brightness itself.
The result contradicts popular beliefs since the circadian cycle of rodents is elongated under yellow light and reduced under blue light, with, whatever happens, an elongated cycle if the luminosity is increased.
"Our results suggest that the use of dimmed, cooler, evening and warmer lights during the day may be more beneficial," explains Dr. Tim Brown, recalling that this study conducted on mice could possibly be verified on other mammals, such as primates (and therefore humans), but this has not yet been demonstrated.
Uninteresting night mode ?
Should we therefore completely stop using the night mode of our smartphones ? Not really. Indeed, Dr. Tim Brown makes it clear that this study concerns equal luminosities and that the current approach leads to lowering the luminosity by reducing the blue lights. You can also see this by switching your smartphone to night mode on a dark image and noticing that it becomes more difficult to view.
According to this study, the night mode would therefore send “mixed” signals to the brain since yellow light would tend to lengthen our circadian cycle where the reduction in brightness would tend to shorten it. In addition, the tests were carried out with "blue" lights with wavelengths of 385 and 460 nm, with a strong dominant of waves approaching turquoise (490 nm). However, turquoise waves were already announced by some as beneficial for the circadian cycle, unlike blue-violet (even shorter waves).
These blue lights can cause more serious problems
Moreover, beyond the circadian rhythm, blue light filters for our screens have other interests. Indeed, studies tend to show that these blue lights can cause more serious problems such as cataracts or retinal lesions that can lead to the creation of blind spots or faster aging of the retina.
As you will have understood, the best way to protect yourself is to avoid screens, day and night.
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