The clock in our eyes

7 minute read

We all love our digital devices, but is our exposure to their blue lights causing us sleepless nights?


We all love our digital devices, but is our exposure to their blue lights causing us sleepless nights?

When was the last time you experienced complete darkness? Since Western cities were strung with electric lights over a century ago, only the rare blackout has interrupted the near-constant glow.

Even when the artificial lights are finally switched off, the blue hue from smartphones or laptops illuminates our bedrooms.

“The advent of the artificial light bulb happened relatively recently in our evolutionary history,” Ignacio Provencio, a professor and biologist at the University of Virginia told The Medical Republic.

“We are simply not wired up to be exposed to light in the evening.”

All this artificial light is believed to be a cause of increasing sleep disorders, with light from mobile electronic devices emerging as a particular culprit.

A review of 20 studies published this month in JAMA Pediatrics found that children who used electronic devices around bedtime were more likely to have poor sleep and feel tired during the day.

The authors labelled the deleterious effect of light on sleep “a major public health concern” and encouraged interventions by family doctors.

“Mobile devices have invaded the bedroom,” an accompanying editorial warned.

Children today had unprecedented access to technology and were increasingly exposed to “biologically potent” wavelengths of light from mobile devices and LED lamps, the editorial said.

The combined effects of sleep deprivation and disrupted circadian rhythms could lead to a range of health problems, including obesity, reduced insulin sensitivity, greater type 2 diabetes risk, impaired immunity, degraded memory consolidation, anxiety and depressed mood, the editorial said.

“There is no doubt that being on a gadget for an hour or two before bedtime can stimulate the brain,” Dr Dev Banerjee, sleep specialist and medical director of the Woolcock Institute in Sydney, told The Medical Republic.

There is now a body of research connecting blue light exposure to suppression of melatonin production and interrupted sleep patterns.

Exposure to an electronic tablet for two hours has been shown to suppress melatonin production by the brain by about 22%.

A 2014 study found that people using light-emitting eReaders produced less melatonin and took longer to fall asleep than those reading old-style paper books.

“We tend to hold [electronic devices] close to our face so they are actually relatively bright compared to the surrounding light,” Professor Provencio said. “So they can be very alerting and they are very rich in the blue wavelengths.”

The allure of these devices is such that 45% of Australians surveyed in 2014 said they brought them into the bedroom.5

But it’s not just handheld devices that are the problem; room lights also have an impact on sleep. A 2011 study showed that exposure to electric lights before bedtime shortened melatonin production duration by about 90 minutes and resulted in later melatonin onset in 99% of study participants.6

Why orange is the new black

So why is blue light so stimulating compared with other colours? The answer lies in our evolution.

When blue light hits the melanopsin photopigment in the retinal ganglion cells at the back of the eye, this sends a signal to the pineal gland in the brain and shuts down melatonin production.

In the mornings this process wakes us up. A blast of sunlight kickstarts a cascade of biological processes, setting the body up for the day’s metabolic, physical and mental activity.

But when the eye senses this blue light at night, it delays the onset of melatonin production and prevents sleepiness.

Smartphones, tablets and TVs emit bright blue light. But selectively blocking the blue wavelengths can help alleviate the impact of this light at night.

“I have a program called f.lux [on my computer],” said Professor Provencio. “It removes the blue wavelengths as evening progresses with the hope of not stimulating these photoreceptors.”

F.lux has been downloaded more than 20 million times since it was released for free in 2009. Orange-tinting software also exists for mobile phones, under the brand name Twilight for Android devices and Night Shift for iPhones.

Amber-tinted glasses have also proved successful at eliminating the ill effects of blue light, improving sleep quality and mood.

It is possible to create an ideal “light diet” using artificial lights. For instance, NASA is developing a programmable lighting system for astronauts aboard the International Space Station to help regulate sleep cycles.

Back on earth, however, some modern environments are unwittingly exacerbating the problem.

“One of the places where lights are on all the time are hospitals, and that’s a huge issue,” Professor Provencio said. “Some hospitals are even experimenting with turning off the blue wavelengths in the evening.”

Removing light sources entirely was the easiest way to get a good night’s sleep, according to Dr Banerjee, who recommended full electronic abstinence before bed.

“It’s not just the light but also the content that person is engaging with … that promotes alertness,” he said.

“Having a dim light or blue-blocking orange light, that will obviously lessen the impact of delaying melatonin, but at the end of the day the critical thing is just switch off the gadget.”

Dr Banerjee admits to being a night owl and regularly checks emails in the evening.

“But I certainly don’t take my gadget to bed,” he said. “The bedroom is for sleep, it’s not for social media. I don’t take it in the room so that no one can disturb me apart from a possum that’s running up my roof.”

Light is the most potent way to reset the biological clock, but the mechanism behind this was not known prior to Professor Provencio’s work. His research during the mid-1990s led to the discovery of a previously unknown organ in the eye.

He and his colleague, Mark Rollag, found a novel protein called melanopsin in the skin of the African clawed frog. This was later found inside a previously unknown type of human eye cell called intrinsically photosensitive retinal ganglion cells (ipRGCs).

“These ipRGCs have this light-sensitive protein melanopsin in them and, subsequently, it was shown by multiple labs that these project right to the clock in the brain and they are involved in resetting the clock,” Professor Provencio said.

“Where this all fits in with the use of smartphones is that the wavelengths of light, the colour of light that optimally activate these ipRGCs, are the blue wavelengths.”

Interestingly, people who are blind can usually still regulate their biological clock using these non-visual light sensors in the retina, even though their rods and cones are non-functioning.

“In the past, some ophthalmologists would recommend that if you were cognitively blind you just have your eyes removed because, frankly, they can be a source of infection,” Professor Provencio said.

“What was not appreciated about 10 years ago was that when they remove the eyes they are also removing their ability to detect non-visual light.”

The consequences are severe. Without light, the internal clock can become 12 hours out of phase with the astronomical cycle within several weeks, leaving the person with a feeling of perpetual jet lag.


1 JAMA Pediatr. 2016, online 31 October

2 Sleep. 2006 Feb;29(2):161-8.

3 Appl Ergon. 2013 Mar;44(2):237-40.

4 Proc Natl Acad Sci U S A. 2015;112(4):1232-7.


6 J Clin Endocrinol Metab. 2011; 96(3): E463–E472.

7 Chronobiol Int. 2009;26(8):1602-12.

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