Scientists have challenged the effect of screen color on a person's internal clock

For a long time it was believed that bluish (for technical reasons) light from gadgets negatively affects the work of the body's internal clock. Recently, Swiss scientists have found that there is almost no difference between it and yellowish light (which is what appears when you turn on the night mode on your phone).

Evening exposure to short-wave light can affect the circadian clock, sleep and attentiveness. Light-sensitive retinal ganglion cells expressing melanopsin are thought to be the main drivers of these effects. But scientists didn't know whether color-sensitive cones, which are the three types of cells in the retina responsible for color vision, also contribute. They perceive three colors separately: red, green and blue.

If light consists only of short wavelengths between 440 and 490 nanometers, we perceive it as blue. If short-wavelength light activates ganglion cells, they signal to the internal clock that it's daytime.

In 2019, scientists found that yellow light has a stronger effect on the internal clock than blue light. In a new study, experts from the University of Basel (Switzerland) refuted this. The results of their work were published in the journal Nature Human Behavior.

With the help of the experiment, scientists tried to find out how light stimuli affected the internal clock of a person, how long it takes to fall asleep, and how deep their sleep was. In addition, the authors of the work checked the level of fatigue and sleepiness.

Sixteen people participated in the study. The experiment itself lasted 23 days, during which the subjects visited the sleep lab a total of four times: they spent one adaptation night and made three visits of 32.5 hours per protocol to assess the effects of light exposure. They were exposed to bluish or yellowish light for one hour before sleep and to white light as a control.

The light stimuli differentially activated color-sensitive cones in the retina. However, stimulation of light-sensitive ganglion cells was similar in all three conditions. Thus, the differences in the effect of light were directly linked to the corresponding stimulation of the cones.

As a result, the scientists found no evidence that changing the color of light plays an important role for the internal clock or sleep. Admittedly, it's unclear whether this would work for longer exposure to a bluish light source, since plenty of people spend more than an hour a day on their smartphone. To clarify the situation for such cases, the authors of the work hope in future studies.

Modern people by the number of hours sleep significantly more than people in natural conditions (hunter-gatherers), but sleep very poorly. This leads to an increased likelihood of depression, reduced concentration and attentiveness during working hours. In the last few years, poor sleep quality has been attributed to gadgets with their bluish light from the screen. This fashion has been followed by the emergence of many "light filters" - applications that make the light from a smartphone in the evening yellowish. The authors of a new paper have questioned their effectiveness.