The color of light is less important for sleep than you might think

The color of light is less important for sleep than previously thought. As a research team from the University of Basel shows in a new study, people sleep equally well regardless of whether they are exposed to yellow or blue light in the evening.

The starting point for the study published Friday in the journal ‘Nature Human Behavior’ was a 2019 study in mice. This suggested that yellowish light has a stronger influence on the internal clock than bluish light, according to Christine Blume of the University of Basel points out that research by the Keystone-SDA news agency has explained.

The results of this study four years ago led many to conclude that night mode on smartphones could have negative effects on sleep. This causes the colors of the display to appear yellowish. The new findings of the researchers from Basel contradict this.

But you could design smartphones’ night modes differently, Blume explains. According to Blume, changing the color spectrum would not be necessary. “That’s a side effect. Technologically speaking, it would be entirely possible to reduce the shortwave light component without color adjustment.” said the sleep researcher.

In their study, researchers from the University of Basel and the Technical University (TU) of Munich compared the influence of different light colors on the human body, as the University of Basel explained in a statement. To do this, the researchers exposed 16 subjects in the late evening to a blue or yellowish light stimulus for an hour, and as a control condition a white light stimulus.

The light stimuli were designed in such a way that although they activated different cones responsible for color vision, they always stimulated the so-called ganglion cells in the same way. Ganglion cells are nerve cells that collect information from photoreceptors and send it to the brain via the optic nerve. This allowed the role of light color to be determined independently of other factors.

In the sleep laboratory, they determined whether the color of light changed the test subjects’ internal clock, how long it took for the test subjects to fall asleep and how deep their sleep was at the beginning of the night. They also asked about their fatigue and tested their reaction time, which decreases as sleepiness increases. They found no evidence for changes in these factors across different types of light, as the study shows. (saw/sda)