There's a lot of evidence that blue light, emitted by smartphones, tablets, laptops, and many other electronic devices, is impacting on the quantity and quality of the sleep we are getting. Darkness is a natural cue to our bodies that it's time for sleep, but we're circumventing it by staring at bright screens for hours after the sun has gone down.

You can decrease your exposure to blue light in a variety of ways, beyond turning off all the light sources. There are special filters, glasses, light bulbs, and even software you can use. But, before we get into that, let's delve into the science behind it.

What's the problem with blue light?

Blue light tells our brain that it isn't time to sleep, according to the experts.

"There are about 30,000 cells inside your eye that are reactive to the wavelength of light which would be considered blue," explains clinical psychologist and sleep therapist, Dr. Michael J. Breus. "Blue runs in about the 460 nanometer range, in terms of the spectrum of light. That particular spectrum of light hits these cells and makes them send a signal to an area of the brain known as the suprachiasmatic nucleus and tells it to turn off melatonin production. Melatonin is the key that starts the engine for sleep."

The impact of blue light has been well-known to sleep researchers and scientists for many years now. Our circadian rhythms determine our internal clocks. Someone who routinely stays up late probably has a longer rhythm than an early riser. Daylight traditionally keeps those rhythms aligned with our environments. Blue light therapy is frequently used to shift sleep patterns and tackle sleep disorders.

"In the past 50 years, there has been a decline in average sleep duration and quality, with adverse consequences on general health," so begins an illuminating paper entitled, Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness, based on research from Harvard Medical School, amongst other places.

The paper assessed two groups; half read a normal printed book for four hours before bedtime for five consecutive nights, while the other group read a light-emitting ebook reader for the same period. The patients using the ebook reader showed suppressed levels of melatonin. On average, they took 10 minutes longer to fall asleep and displayed significantly less rapid eye movement (REM) sleep than the group reading printed books.

Unsurprisingly, the ebook reader group reported feeling less tired in the evening, but they also reported that they felt more tired in the morning, despite having the same duration of sleep as the other group.

There are more serious health issues to consider if you aren't getting enough sleep. When our circadian rhythms are thrown off researchers believe we are put at more risk of all sorts of things including heart attacks, obesity and type-2 diabetes, and various cancers. Those examples are mostly related to long term night shift, or severe sleep disorders, but any disruption to your circadian rhythm can cause problems. Lack of sleep has also been linked with mood problems, anxiety and depression, and increased risk of accidents.

Can blue light damage our eyes?

There are also some scientists linking blue light to age-related macular degeneration, though the evidence doesn't seem to be conclusive. Over exposure could be playing a role in the rise of cataracts and even blindness.

"We are seeing a much greater number of age-related macular degeneration patients, even back correcting for the aging population, so the risk factors are clearly changing," explains Professor John Marshall, Frost Professor of Ophthalmology at the Institute of Ophthalmology in London, "If you look at cataracts there's a very good correlation between the age of onset of cataracts and the degree of ultraviolet where you live in the world, that's why people close to the equator tend to get their cataracts 5 to 10 years earlier."

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We know ultraviolet (UV) is damaging and the blue range is closest to it. For damage to the eye, the peak wavelength for blue light is around 440nm, but the suppression of melatonin is higher, at around 460nm.

"By far and away the biggest exposure you're going to get is from the sun -- that is the biggest blue light hazard that you will meet in your lifetime," says Professor Marshall. "The big red herring here is smartphones. If you actually do the calculations from the spectral emission of those things -- it's tiny."

The risk of damage has a great deal to do with power and brightness.

"Light bulbs are much brighter sources," explains Prof. Marshall. "When was the last time you got an after image from looking at your iPad? When you look at a light source, especially an LED, you've got that multicolored image on your retina which takes a long time to fade."

LED light bulbs may be worse than your phone

The electric lights in our homes may be having a bigger impact than our devices. The paper Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans, found that exposure to room light before bedtime suppressed melatonin in 99 percent of individuals and shortened melatonin duration by about 90 minutes.

"Until recently, we lit our homes with incandescent bulbs and they were relatively biologically friendly, in that there was very little blue," says Prof. Marshall, "More commonly now they're LEDs and these light sources have a lot of the potentially damaging blue, to the extent that I don't use them."

There's a Florida company called Lighting Science Group which offers a line of "biological" lighting. You might opt for a warm light bulb that emits lower levels of blue light for your bedroom, and use an Awake & Alert bulb in the kitchen to get you going in the morning along with your first cup of coffee. There is evidence that the bulbs we use can also impact on our circadian rhythms, and worse, affect our skin the way that the sun does, but this usually requires close, prolonged proximity.

A lot of bright lighting is obviously going to be an issue, that's often a problem for night shift workers, depending on their environment. For most of us, subdued lighting towards bedtime is going to be enough to make a difference. But, what about the blue light coming from our devices?

If you're really concerned about blue light exposure, then there are bigger fish to fry than smartphones and tablets.

"Wear a big hat, appropriate sun glasses, and consider the lighting in your home," says Professor Marshall. "If it's iPads and iPhones, I wouldn't worry."

The right balance of blue light

"There's nothing wrong with blue light for most of the day," says Dr. Breus. "You just don't want to have it about 90 minutes or so before bed."

Sunlight has a tremendous amount of blue light in it. The worrying negative effects are connected with the melatonin deficit and disruption of circadian rhythms that leads to less sleep and poorer quality sleep. But, we need blue light to get us going in the morning, and it has been linked with higher levels of alertness.

"When we wake up in the morning our circadian rhythm is a little off, our internal biological clock runs on a slightly longer schedule in many cases than 24 hours, and so to reset that clock every morning we need sunlight," says Dr. Breus. "One of my biggest recommendations for patients is every morning go outside and get 15 minutes of sunlight."

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At the other end of the day we need to be more mindful of our blue light exposure. Proximity is an important factor. That's why smartphones, tablets, and laptops are perceived as a bigger risk than light bulbs or TV screens. Though, it's worth remembering that the impact on sleep is about more than just the blue light exposure.

"I think there's a second factor that people aren't really talking about that much, and that is the level of engagement in whatever the device is," explains Dr. Breus. "If you're playing your favorite game, or whatever it is you like to do before you go to bed, you're mentally engaged in that act."

Let's be honest, turning everything off and sitting in a dark room is not something many of us will do. Thankfully, there are alternatives.

How to filter blue light with special glasses

There have been protective glasses on the market for a while, but they tend to have colored lenses. Now, we're beginning to see alternatives that aren't so strongly tinted, such as the Jins Screen range of glasses, which have been specifically developed to address the blue light problem.

"They reduce the transmission of light in the 460 nm range by 25 percent via two pathways: coating and substrate," explained Lilian Wouters, PR Manager at Jins. "Certain wavelengths of blue light are reflected by the patented coating on the lenses, while others are absorbed by the substrate, which is made of a compound that absorbs certain wavelengths of blue light."

You can pick them up as standalone non-prescription specs, but the special coating will also be available on prescription glasses.

There's also a newcomer on the scene, called Gauss, which recently smashed its Kickstarter target.

"Gauss glasses come with lenses that have multiple layers of coating applied to them. Each layer has different properties and all this combined results in our Blueguard coating," developer Jay Uhdinger told us. "It reflects light peaking with the wavelengths of 400 to 440 nanometers, while still letting other wavelengths pass through, to enable people to still see blue as blue with minimal impact on normal color vision. Studies show that these frequencies can cause most damage to the retinal pigment cells of the eyes."

With self-tinting lenses and UV blocking, Gauss glasses are intended to serve as sunglasses and offer indoor protection. They are designed primarily to protect your eyes against the potentially harmful 440nm peak blue light, but they do also filter 460nm light that might impact on your melatonin production.

"Our goal was to create the perfect sunglasses for the digital age because it is simply easier for people to carry around one pair of glasses that they can use to protect their eyes while they are outside or when sitting in front of a computer or other digital device screen," says Uhdinger.

The science behind these glasses appears to be sound. There is a lot of research on lenses that block blue light and they do seem to have a positive impact on sleep quality. Jins was also a sponsor of the recent New York Blue Light Symposium which had various academics presenting research on blue light and its negative impacts.

Why not use software?

One of the most popular options right now is F.lux. It tweaks the color of your computer's display according to the time of day, so it gets warmer at night and has more blue throughout the day. It's completely free and you can use it on Windows, Mac, Linux, and jailbroken iOS devices. There's an app called Twilight on Android that does the same thing.

We asked Uhdinger why people would use glasses over software and here's what he said,

"We think apps like F.lux or Twilight are great and everyone should use them. In fact, they should be part of future operating systems. Gauss glasses just add another layer of protection because unless you completely turn off the blue color channel in your monitor it still emits blue light. Plus many other sources of blue light like light bulbs with cold color temperatures still emit blue light that interferes with your melatonin production and as a result, with your circadian rhythm."

What works to reduce blue light?

I've been using Twilight and F.lux for a couple of weeks and it does feel like it's made a difference. Just like millions of other people, I tend to read on a screen in bed, with no other light source, and since using the apps I have felt tired earlier and fallen asleep more easily than before. Judging by the reviews and discussion online, a lot of people feel the same way.

I'll be getting a hands-on look at the Gauss glasses very soon, so stay tuned for more on that.

In the meantime, think about your exposure, and if you're having trouble sleeping, try modifying your lighting and device use. Blue light is just one of the factors that determines your sleeping pattern, but it's clearly very important. Some experts recommend staying away from devices for a half hour before sleeping.

"Would I say we have a health problem because of phones and tablets shining light in our faces? I would say, yes we do," Dr. Breus told us. "But, they're not the only factor."

You can find more advice on getting healthy sleep at his Secrets to Sleep Success website.