Let there be 'circadian' light
New study describes science behind best lights to affect sleep, mood and learning
February 20, 2020
Science Daily/University of Washington Health Sciences/UW Medicine
Researchers said the wavelengths at sunrise and sunset have the biggest impact to brain centers that regulate our circadian clock and our mood and alertness.
Their study, "A color vision circuit for non-image-forming vision in the primate retina," published in Current Biology Feb. 20, identifies a cell in the retina, which plays an important role in signaling our brain centers that regulate circadian rhythms, boost alertness, help memory and cognitive function, and elevate mood.
These effects have been attributed to a pigment in the eye called melanopsin, which is sensitive to blue light, but researchers say cone photoreceptors are a thousand times more sensitive to light than melanopsin. The cone photoreceptor inputs to the circadian circuity respond to short wavelength blue light, but they also respond strongly to long wavelength oranges and yellows and contrasting light -- the colors at sunrise and sunset. What makes good lighting, researchers discovered, is lighting capable of stimulating the cone photoreceptor inputs to specific neurons in the eye that regulate circadian rhythms.
Lead author Sara Patterson, a graduate student in neuroscience at the University of Washington School of Medicine, said how we set our internal clocks to the external light-dark cycle has been studied a lot. But how the changes in the color of light affect our brain has not.
"Color vision used for something other than color perception was the most exciting part for me," she said.
In the study, Patterson and colleagues identified a cell known as an inhibitory interneuron or amacrine cell in the retina, which signals to photosensitive ganglion cells that affect our circadian brain centers. The researchers said these amacrine cells provide "the missing component of an evolutionary ancient color vision circuit capable of setting the circadian clock by encoding the spectral content of light."
Patterson said so little is known about rare retinal circuitry that it was possible to find a new blue cone cell. She said there is a lot more to be discovered about how blue cone cells are projecting to other areas of the brain.
While sunrise lights, blue lights and seasonal affective disorder (SAD) lights have all tried to capture benefits of natural light, they haven't been that effective because they are missing key science data, said corresponding author Jay Neitz, professor of ophthalmology at the UW School of Medicine, a scientist at the UW Medicine Eye Institute, and a well-known color vision researcher. He said the science behind SAD lights, for example, is to make lights hundreds of times brighter than normal lights to stimulate melanopsin.
"This research all started because of our interest in the health benefits of having natural light that occurs at the right time of day that helps regulate our circadian clock and our mood and alertness," Neitz said.
The University of Washington has licensed technology based on this discovery to TUO (https://www.thetuolife.com/), a lighting technology company that will be selling white LED lightbulbs that will incorporate undetectable sunrise and sunset wavelengths for commercial use.
The work was supported by the National Eye Institute and Research to Prevent Blindness. Other collaborators include James A. Kuchenbecker, research scientist/biomedical engineer with the Department of Ophthalmology at the University of Washington School of Medicine; James R. Anderson, research scientist/software architect with the John A. Moran Eye Center at the University of Utah School of Medicine, and Maureen Neitz, professor of ophthalmology at the University of Washington School of Medicine.
https://www.sciencedaily.com/releases/2020/02/200220141731.htm
Blue light may not be as disruptive to our sleep patterns as originally thought
December 16, 2019
Science Daily/University of Manchester
Contrary to common belief, blue light may not be as disruptive to our sleep patterns as originally thought -- according to scientists. According to the team, using dim, cooler, lights in the evening and bright warmer lights in the day may be more beneficial to our health.
According to the team, using dim, cooler, lights in the evening and bright warmer lights in the day may be more beneficial to our health.
Twilight is both dimmer and bluer than daylight, they say, and the body clock uses both of those features to determine the appropriate times to be asleep and awake.
Current technologies designed to limit our evening exposure to blue light, for example by changing the screen colour on mobile devices, may therefore send us mixed messages, they argue.
This is because the small changes in brightness they produce are accompanied by colours that more resemble day.
The research, which was carried out on mice, used specially designed lighting that allowed the team to adjust colour without changing brightness.
That showed blue colours produced weaker effects on the mouse body clock than equally bright yellow colours.
The findings, say the team, have important implications for the design of lighting and visual displays intended to ensure healthy patterns of sleep and alertness.
The study is published in Current Biology and funded by the Biotechnology and Biological Sciences Research Council.
The body clock uses a specialised light sensitive protein in the eye to measure brightness, called melanopsin, which is better at detecting shorter wavelength photons.
This is why, say the team, researchers originally suggested blue light might have a stronger effect.
However, our perception of colour comes from the retinal cone cells and the new research shows that the blue colour signals they supply reduce the impact on light on the clock.
Dr Tim Brown, from The University of Manchester, said: "We show the common view that blue light has the strongest effect on the clock is misguided; in fact, the blue colours that are associated with twilight have a weaker effect than white or yellow light of equivalent brightness.
"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 colour."
He added: "We argue that this is not the best approach, since the changes in colour may oppose any benefits obtained from reducing the brightness signals detected by melanopsin.
"Our findings suggest that using dim, cooler, lights in the evening and bright warmer lights in the day may be more beneficial.
"Research has already provided evidence that aligning our body clocks with our social and work schedules can be good for our health. Using colour appropriately could be a way to help us better achieve that."
https://www.sciencedaily.com/releases/2019/12/191216173654.htm