Smartphones may affect sleep – but not because of blue light


Children are more sensitive to blue light, so any potential effects may affect them more, but another sign that blue light may not be the problem is the different impact of interactive screens versus passive screen use. Relaxing in front of the TV, or reading on your phone, is more relaxing than playing video games or messaging in a group chat, even when the blue light exposure is the same.

Another problem related to the way we use screens is that we tend to stare intently, blinking less often, which can dry out our eyes. Whether you call it computer vision syndrome or digital eye strain, most of us have experienced itchy or red eyes, blurred vision, headaches, or neck or back pain at one time or another, usually after working at a computer. Experts continue to recommend the “20-20-20” rule: Every 20 minutes, try to look at an object at least 20 feet away for at least 20 seconds.

Can blue light glasses or filters help?

An entire industry has sprung up out of concerns about blue light exposure. You can buy blue light-blocking glasses, filters and special light bulbs, not to mention software options including dark mode. But do any of them actually help, or is it just scaremongering designed to sell technology?

Pierson says theoretically they could work, but the evidence is not straightforward. He highlights this review, which suggests a positive effect on sleep latency for people with sleep disorders, jet lag and variable shift work. But he says the problem with most studies is that participants’ actual light exposure is not measured, and the wavelengths these filters block are often poorly described.

Blue light has a shorter wavelength (between 400 and 495 nanometers) than red light (620 to 750 nanometers). But different filters block different wavelengths, making them difficult to compare. Cutting out longer wavelengths may be more effective at reducing light exposure to our circadian rhythm (our natural sleep/wake cycle), but it can also affect visual function, making it harder to see, Pierson says.

This review from the Cochrane Library examined a number of studies and found “no clinically meaningful difference” between normal lenses and lenses that filter out blue light. The American Academy of Ophthalmology and the College of Optometrists in the UK say there is no evidence that the blue light emitted from screens is harming our eyes, and neither do they recommend blue light-blocking glasses.

This study of blue-light filter apps shows they don’t improve sleep either, and dark mode might not be as good for your eyes as you think. So what should we do?

lights out

If you’re concerned about getting a good night’s sleep, establishing a bedtime routine is key. According to sleep expert Sophie Bostock, the intervention with the strongest evidence base is cognitive behavioural therapy for insomnia (CBT-I). She was part of the team working on Sleepio, the program that cured my insomnia. It’s a six-week course that covers a variety of simple techniques:

  1. Wake up at the same time every day.
  2. Use a sleep diary to keep track of your sleep patterns.
  3. Don’t go to bed unless you feel sleepy.
  4. When you can’t sleep, get out of bed.
  5. Use cognitive techniques to clear your mind of racing thoughts, such as mindfulness, journaling, and cognitive reframing.

Bostock also says that if you get plenty of natural light during the day, your body clock will be less sensitive to the effects of light at night. Taking a morning walk or having coffee in the garden before starting work can help get your circadian clock on track.

Blue light has the potential to harm us, but it can also be good for us. One study exposed students to either artificial blue light or warm white light for an hour every morning and found that blue light not only decreased melatonin levels; many students also reported higher alertness, positive mood, and visual relaxation.

As with most things in life, balance is key. Ultimately, you should avoid bright lights before bed, but you don’t have to worry about the blue light emitted by dimly lit smartphone screens or TVs.

That being said, it’s probably a good idea to take a break from screens at night, especially for kids. Podcasts and audiobooks are a great way to unwind without screens. And if you must use your smartphone in bed, follow this very simple rule: focus on fun things and avoid anything stressful.


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