Orange “sleep sunglasses” are trendy, but the scientific premise behind them could be misguided.
A recent study reports that 90% of mammalian species possess the ability to sync behavioral and biological cycles to the position of the sun based on the color of the sky. Our brain analyzes the change in the spectrum of light between blue and yellow during dawn and dusk, specifically, in order to keep the body’s rhythms on track.
The control center of our brain’s 24-hour biological clock is the suprachiasmatic nucleus (SCN), located in a part of the brain called the hypothalamus. The team of scientists working on this research found that neurons in the SCN of mice are sensitive to color—specifically, the spectrum we see during twilight. Scientists have long known that the quantity of light (what they called “irradiance”) dictates internal circadian clocks. But this is the first time that experts have isolated the effect of color and shown that the quality of light (not just the amount of it) matters when it comes to body clock moderation.
Tim Brown, a BBSRC Research Fellow at the University of Manchester in the U.K., was an author on the study, published in PLOS Biology in April. He conducted a Reddit AMA this week in which he discussed possible applications of the team’s research.
Importantly, however, while melanopsin is very important for measuring brightness it cannot actually detect colour. E.g. a violet light and a yellow light of equal photon flux would produce an identical response. To detect colour one needs to compare the activation of at least two different types of light sensitive protein each with different spectral sensitivities. For this you need cone photoreceptors and that is what our new research shows constitutes a parallel pathway for telling the clock time of day. Our work also suggests that the blue signal from the cone pathway signals ‘night’ (whereas the more green-blue signal from melanopsin signals ‘day’).
So it’s not necessarily the blue pigments in computer screens that are messing with our sleep patterns. It could be the amount of light, or something else—the point is that both color and irradiance influence how our bodies tell the time of day. Deeper studies may consider the combined effect of signals coming from melanopsin, rods, and cones on color-sensitive SCN neurons, as well as how orange sunglasses may alter the irradiance of light.
It may turn out that programs like f.lux are only coincidentally successful, so more advanced research in this new direction could lead to better sleep-regulating technologies. We may even be able to stretch or compress the length of human sleep cycles—though Brown acknowledges that this research first must be translated from mice to humans in order to understand it fully.
Photo credit: L'hò / Flickr (CC BY-NC-ND 2.0)