What is blue light and should you care about it?

One of the more contradictory trends in tech over the past few years has been the integration of so-called digital wellness features. These days, it’s not uncommon to find tech that wants you to use it a little less. 

At first blush, that might sound a little counterintuitive. However, most Aussies would admit to spending a little too much time on their devices nowadays. The addition of new software settings designed to push consumer behaviour in the opposite direction is in some ways just a natural response to that demand. 

More than just new software like the digital well-being tools that Apple and Google are building into their respective operating systems, this drive towards the reduction of potential harms has brought with it new hardware features. 

Ironically, the emergence of built-in blue light filters on devices as small as a smartphone and as large as a TV is one of the most visible such digital wellness settings. However, the truth of whether blue light filters are actually something you should care about is more than a little hazy.

Blue light is exactly what it sounds like, but you can’t really talk about it without first talking about how human vision works. 

The simple version: when we open our eyes, our retinas absorb incoming light. Our brains unscramble that raw data into images. There are lots of different kinds of light. Human eyes are capable of seeing some, but not all of it.

The slice of frequencies that our eyes can handle is called the visible light spectrum.  When your eyes are exposed to any screen based around light-emitting diodes (LEDs), they absorb what is called white light. This type of light is made up of every colour in the visible light spectrum. That includes blue light, which is aptly named after the colour that our brains process it as.

While LEDs do emit greater amounts of blue light than older lighting technologies, it's worth noting that the former still pales in comparison to the biggest source of blue light that most people will encounter: the Sun.

Speaking to Reviews.org, Optometry Australia chief clinical officer Luke Arundel said that studies have suggested that high intensities of blue light can damage retinal cells.

However, he noted that the majority of research conducted involved animal models and intensities far greater than that emitted from digital devices. 

As you might expect, a blue light filter is something used to filter the blue light part of a white light out of the spectrum. In its most basic form, there are no fancy moving parts or electrochemical trickery involved.

Most blue light filters are exactly what they sound like. They're made up of an ultrathin material that either block, absorb or otherwise reduces the amount of blue light projected by the white light emitted by a given screen.

The rest of the spectrum passes through the filter to reach our eyes. Blue light does not.

Blue light filters promise to promote digital wellness and improve your broader health by reducing the amount of blue light that our eyes are exposed to. 

The hope is that a reduction in blue light will also reduce the incidence of the symptoms that are sometimes associated with or attributed to high blue light exposure, such as headaches, eyestrain, and poor sleep.

Describing blue light as "implicated" when it comes to eye strain and computer vision syndrome, Mr Arundel noted the limited size and reliance on anecdotal evidence when it comes to blue light filters.

While the notion of filtering out the “bad” light from our screens has an appealing ring to it, the scientific basis for the benefits of blue light filters is far from undisputed.

It is true that the experience of spending too much time looking at your laptop or smartphone screen that your eyes begin to feel sore is hardly rare. However, many of those symptoms have less to do with blue light exposure and more to do with the way we use our devices. 

When you’re staring at any screen for hours at a time, blue light or not, you may incur some symptoms that emerge under the broader banner of digital eye strain or computer vision strain.

As put by the American Optometric Association, “many individuals experience eye discomfort and vision problems when viewing digital screens for extended periods. The level of discomfort appears to increase with the amount of digital screen use.”

Blue light doesn’t really play much of a role here. 

Digital eye strain has more to do with how we use our devices than it does the kinds of light they do or don’t emit. If you’re staring at a screen for too long at the wrong viewing or in an environment with poor lighting, that’s the kind of situation that can lead to digital eye strain. 

According to one report published in 2020 by the Royal Australian and New Zealand College of Ophthalmologists (RANZCO), the key to harm reduction when it comes to digital eye strain is as simple as taking regular breaks.

So far as general eye hygiene is concerned, the case for blue light filters seems pretty flimsy. 

The other narrative that tends to crop up around blue light filters is that blue light reduction can help improve your sleep. The answer to this question is more complicated because blue light does have a role to play when it comes to how sleep cycles.

Mr Arundel explained that exposure to blue light naturally suppresses the production of a hormone called melatonin. More melatonin makes you drowsy, priming you for sleep. Less melatonin produces the opposite effect.

"When our eyes are exposed to blue light we suppress the production of melatonin and this tells our body to wake up.  Conversely, without blue light, our body produces more melatonin which helps us get ready for sleep," he said.

For the reasons described above, melatonin is typically framed as the hormone that shapes your sleep cycle. However, experiments have shown that this biological mechanism can be tricked by exposure to light, shifting your circadian rhythms by hours at a time.

One test found that blue light had a more pronounced effect in this regard than some other types of light.

Mr Arundel admitted that the use of devices that emit blue light can play a role in sleep disruption, but emphasised the limitations of the research that's been done into the topic.

Another study, conducted by the University of Houston in 2017 found that those who used blue light filters in the three hours before they went to bed recorded a 58% increase in melatonin levels.

That figure sounds really high. However, the study itself only involved a sample of 22 participants. 

More broadly, melatonin production and blue light exposure are only one of many factors that affect sleep quality.

It’s hard to untangle the influence of either from the many other possible variables in the mix, let alone the baseline effect that looking at any LED screen for long periods of time can have on your sleep cycle.

"There are however many components which contribute to digital eye strain or computer vision syndrome and while research in this area continues, there is currently no metadata or high-level evidence to support wearing of blue light-blocking glasses for eyestrain," Mr Arundel told Reviews.org.

He's not the only sceptic out there in the professional world of eye care.

The American Academy of Ophthalmology (AAO) has gone so far as to say that there is no credible scientific evidence that the light from digital screens is harmful.

Australia's own RAZNCO took the same stance.

According to the venerable medical college, filtering out blue light isn't necessary for most people. There may be other benefits to reducing screen time in the evening, but that's not the same narrative that those flinging filters like to peddle.

The little evidence that blue light filters are good for sleep is often conflated as something much more than what it is, and when you think about the commercial implications for those involved, it’s not hard to be sceptical about the reasons why.