Every night at 10:30, my phones screen turns a sickly orange, which makes it difficult to watch my episodes of Bob Ross. The colours are all a messway too warm. Is that actually phthalo blue, or is it Prussian blue? I can never tell. Oh cursed, curly Muse! Its all my fault, really. Because I have a handy feature on my phone that tweaks the screen at night to reduce blue, a colour that supposedly makes you more alert. Not conducive to kicking back with Bob before bed. But really, though? Does blue light actually make you more alert? It sure does. But does removing it from your smartphones screen help you fall asleep? That, my friends, hasnt actually been solidly provenat least not yet. Lets start off by talking about your peepers. You learned in grade school that the retina is made up of rods, which are good in low light, and cones, which are good for colour. But you actually have a third kind of photoreceptor in your eye, calleddeep breathan intrinsically photosensitive retinal ganglion cell. These exclusively subserve the circadian system, says sleep researcher Shadab Rahman of Harvard Medical School. They send out projections from the retina to the parts of the brain that regulate biological timingsleep and alertness. These guys are most sensitive to blue light, so even if you lose your rods and cones somehow, your body can still react to blue by way of these special cells. Studies have indeed shown that exposing subjects to blue light increases their alertness. Why blue? One theory speculates that it may be an evolutionary holdover. Way back when, one of humans mammalian ancestors may have lived a crepuscular lifestylethat is, it emerged to forage at dawn and dusk. During these times of the day, the sky throws off a lot of orange, but blue light is in short supply. So perhaps this mammal evolved to become more sensitive to blue light to build a better picture of its world. What isnt speculative is that the plain white light coming off your iPad is very bad for your sleep, severely mucking up your biological clock. This white light is of course composed of the component colours of the rainbowthats why you get blue and yellow and green and all that when sunlight hits a prism. And the problem with the screen on your phone or tablet is that its particularly blue-enriched, and that blue light does indeed perk up the human brain, even during the day. But evidence is lacking that getting rid of white lights blue component in a dim setting helps. The research just isnt there yet. Scientists have mostly experimented with exposing people to lightmodified to cut out the blue, known as blue-depleted lightat high intensities, say 1,000 lux. (Your average office tallies around 500 lux.) But when we are in our bedrooms, were exposed to light coming from personal devices, were nowhere near close to 1,000 lux, says Rahman. Its about 30 lux, so its much dimmer relatively. A handful of studies have exposed subjects to more realistically dim blue-depleted light for a single nightand those studies have shown some effects. But their results arent statistically significant. When you do these short studies, the effects of this relatively dimmer light are not robust enough that you can catch them in a single night, says Rahman. So you need longer night studies. The bottom line? Theres actually no studies that have systematically seen if blue-depleted light at very dim intensities is effective in preventing or reducing the biological disruption caused by light exposure at night, says Rahman. So that blue dimmer on your phone isnt yet backed by solid science. Complicating matters is the fact that in dim conditions, green light may be as disruptive as blue light, if not more so. So theres a real problem right now in the field that everyone is moving towards this blue depletionyoull hear blue blockers, people wear special glasses, says Rahman. We actually dont know if those work under bedroom-intensity light. So by all means, for the time being let your phone give up blue at night. It wont kill you. But just know that Bob Ross would be very disappointed.
Wired, 30 March 2017 ;http://www.wired.com/news ;