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Blue light and sleep-wake rhythms: a difficult but necessary relationship

An interview with Mariana Figueiro, Director of the Lighting Research Center

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Published: 7 Jan 2020
“Light is like a drug, you have to take it at the right time”, explains Mariana Figueiro, Director of the Lighting Research Center. “People tend to think only about blue light and the colour of light, but the narrative really needs to change. We have to think about time and cyclicity, light and dark, and repeating that every day. Maintaining that regularity is very important”. Our health depends on it, and above all – according to recent reports – the health of our children and teenagers too.
Blue light and sleep-wake rhythms: a difficult but necessary relationship

A participant in an experiment conducted in 2018 on the effects of blue light and
the efficacy of the iPad Night Shift mode (photo: Lighting Research Center)

The Lighting Research Center (hereafter referred to as the LRC) at the Rensselaer Polytechnic Institute in Troy, New York State, is one of the most important research centers in the world with regard to light and its many practical uses. One of the issues that Figueiro and the other experts at the LRC have particularly focused on in recent years in their scientific publications and awareness raising activities is, without doubt, the role that smartphones and tablets play in disturbing users’ sleep-wake rhythms. The effects of screens held so close to peoples’ eyes for such a long time during the day and especially just before they go to sleep, have been shown to be much greater than those of the television screens we have been staring at for decades without anyone getting too worried.

Let’s start from the beginning. Nearly all the animal and vegetable species on this planet have circadian rhythms. These are physiological processes, activated by internal and external factors that are repeated over a twenty-four hour period. “A breakthrough regarding the impact of light on circadian systems came in 1980,” explains Figueiro, “when Alfred Lewy discovered that light suppresses melatonin, a hormone we produce at night, in darkness, that is basically a tiny messenger for the body that tells you it’s night time.”
Blue light and sleep-wake rhythms: a difficult but necessary relationship

A participant in an experiment conducted in 2019 on the effect of light on office workers’ quality of sleep and waking rhythms (photo: Lighting Research Center)

In the same way, when light returns in the morning, it wakes us up “like a cup of coffee” and helps keep us synchronised with our biological clock. But light has the same downside as coffee in that it keeps us awake without making up for the tiredness that sooner or later we end up paying for. Staring at self-luminous screens, like smartphones and tablets, before going to bed, keeps us awake and reduces the quality of our sleep patterns. As more and more people have become aware of this effect, they have begun using applications like f.lux or the Night Shift mode to filter the blue light on their screens in the evening.

A study conducted by the LRC shows that filtering the blue light created by screens really does reduce the suppression of melatonin, but it does not solve the whole problem. “We also need to reverse the polarity of screens by using a black background and white fonts, and emit less light generally. This would mean dimming the display completely, but then, of course, it would become very hard to see anything on the screen. So, I would recommend turning off any self-luminous displays two hours before going to bed, because that’s when you start producing melatonin. If you can’t do that, you need to get a lot of light during the day. So, go outdoors as much as you can during the day, because the more daytime light you get, the less sensitive you are to evening light.”

Paradoxically, notes Figueiro, in recent years buildings have become less bright on account of energy efficiency measures. This means that the people who work in them are less awake during the day and then go home and ruin their sleep by staring at a screen before going to bed.

So, the main problem, according to Figueiro, is not the light but the regularity of the sleep- wake cycle. “One of the things we are learning more and more,” she continues, “is that a lack of sync between your biological clock and your environment is linked to a series of maladies like sleep disruption, lack of performance and increased sleepiness during the day. If this continues for a long time, as with shift workers who have to work at night and sleep during the day, which is the opposite of what they should be doing, the risk of diabetes, obesity, cardiovascular diseases and even cancer increases. Mental health is another area, as a lack of sync is also associated with an increased risk of depression and mental health issues.”
Blue light and sleep-wake rhythms: a difficult but necessary relationship

The same environment lit during the day and at night (photo: Lighting Research Center)

Staring at self-luminous screens, like smartphones and tablets, before going to bed, keeps us awake and reduces the quality of our sleep patterns.
A particularly interesting statistic registered by the LRC is that adolescents between the ages of 15 and 17 are more sensitive than adults to the suppression of melatonin caused by blue light, while other studies have shown that children between the ages of 6 and 8 are even more sensitive. The results of a study conducted in 2015 show that exposing adolescents to a self-luminous screen for an hour suppresses melatonin by about 23%, while exposing them for two hours suppresses it by 38%. In other words, even if people of all ages use electronic devices far too much, children will probably be harmed the most.

Recently, especially since the producers of electronic devices introduced the Night Shift mode, users have become more aware of the potential negative effects of self-luminous screens. Nevertheless, most people haven’t changed their habits very much. According to Figueiro, “it’s like any other addiction, it takes years for you to see the negative impacts, as it’s a pleasure to have a phone or tablet to use and play with.” Actually doing something to recover your natural sleep-wake cycle, on the other hand, “is like going on a diet or exercising. You know exercise is good for you, but it’s up to you to get up every morning and do it. Nobody can force you. If you choose not to, it’s your responsibility.”