Blue light may not be as bad for sleep as suspected, new study argues

For the last few years, general scientific consensus has suggested the blue light spectrum coming out of our modern devices can significantly disrupt our circadian rhythms. To balance this, many devices now come with night modes, offering yellow or sepia screen filters designed to cut out the most problematic blue spectrums of light. Now a new study from the University of Manchester is questioning that common consensus, arguing perceived color can also influence circadian clocks, and novel animal studies may reveal exposure to yellow light at night could be confusing our body clocks.

Alongside the rods and cones in our eyes we have a small amount of innately photosensitive cells. These cells are designed to not help us see, but rather sense light as part of our circadian management system. When these specific retinal cells sense light, they produce a molecule called melanopsin, which directly tells certain parts of our brain to stay awake and alert. As well as suppressing melatonin, melanopsin has been found to help regulate and set our body's circadian rhythm.

The popular blue light hypothesis arose from research finding melanopsin is most sensitive to a wavelength of light around 480 nanometers. This is a blue spectrum of light, and it tends to be the most prominent spectrum displayed by the LED screens used in many of our modern digital devices, from smartphones to laptops.

“There is lots of interest in altering the impact of light on the clock by adjusting the brightness signals detected by melanopsin but current approaches usually do this by changing the ratio of short and long wavelength light; this provides a small difference in brightness at the expense of perceptible changes in color,” explains Tim Brown, corresponding author on the new study. “We argue that this is not the best approach, since the changes in color may oppose any benefits obtained from reducing the brightness signals detected by melanopsin.”

To study the particular influence of color on circadian systems the researchers conducted a series of experiments on mice with altered cone spectral sensitivity. Using polychromatic lighting the study discovered yellow light conferred a greater impact on the animals’ circadian behaviors than blue light.

The researchers go on to hypothesize this innate circadian relationship with color can be related to the organic changes in light composition across twilight in any 24-hour period. The suggestion is the shift towards blue light that accompanies the sun setting is a fundamental influence on our circadian clock.

“We show the common view that blue light has the strongest effect on the clock is misguided; in fact, the blue colors that are associated with twilight have a weaker effect than white or yellow light of equivalent brightness,” says Brown.

This certainly isn’t the first research to explore how the chromatic characteristics of light influence circadian rhythms. However, it is the first to explicitly suggest the perceived color of light can be as influential to circadian systems as spectrums of light that modulate melanopsin.

The research seems implicitly critical of those digital device “night modes” which add a warm yellow hue to screens in the evening. But it is important to note that this new study was only conducted on mice, and although the researchers are confident there is evidence to suggest the effect detected could extend to humans, there is no evidence that the perceived color of light is significantly influential on human circadian systems. In fact, some research has been conducted revealing interventions such as wearing amber-tinted glasses for an hour or two before going to bed may enhance the quality of a person’s sleep.

While it may be clear blue wavelengths of light activate circadian-regulating mechanisms in the human brain, it is not clear yet whether a yellow-filter on a device’s screen markedly influences the human circadian system. So you don’t necessarily need to go and switch off that night mode on your laptop just yet.

The new research was published in the journal Current Biology.

Source: University of Manchester