Sleep hygiene: Understanding the role of light in rest

Have you ever wondered how the light around us affects our sleep? It turns out, the kind of light we’re exposed to can make a big difference in the quality of our sleep. The simple act of flipping a light switch or staring at a screen before bedtime can impact our restful nights.

Light is an important external factor of sleep. The average amount of sleep recommended for adults is seven or more hours. But lights in our homes, electronics, and light pollution outside have made the relationship between light and sleep much more complex. 

Health-e News spoke with Professor Karine Scheuermaier, who leads the Sleep Lab in the Brain Function Research Group  at the University of Witwatersrand. 

She explains how light affects our sleep. 

According to Scheuermaier, exposure to light in the evening makes our brains more alert. So when we read on our phones, tablets or laptops in the evening, it also gives us a boost of alertness, keeping us awake and preventing us from falling asleep quickly.  

“When we are exposed to light (even if only room light brightness) in the early evening, it shifts our circadian rhythms or sleep-wake cycles to a later time. This means we feel sleepy later and fall asleep later. But we may still have to wake up the next morning because of work or school. This ends up curtailing our sleep – which is not good,” she says. 

Scheuermaier says when we are exposed to natural light in the morning (between eight and 10) will advance our rhythms. This is a good thing. It means that we will want to go to bed earlier and wake up earlier. But this will not be the case if we expose ourselves to light in the evening, especially artificial light. 

Light during the day is important 

“Exposure to light during the day has a stabilising effect on our rhythms. In one of our reports we found that during the hard lockdown of Covid for example when South Africans could not get out of the house, they had much more irregular sleep-wake cycles, lost more sleep and were more likely to be anxious and depressed. 

Findings from the report showed that, from a variety of sleep and lifestyle behaviours, difficulties with going to and staying asleep had the most influence on symptoms of depression and anxiety. This relationship was exacerbated during lockdown. 

“So as much as light in the evening can lead to curtailing sleep and disrupting sleep architecture, being exposed to light during the day is really important to maintain regular sleep-wake schedules and good sleep architecture. We shouldn’t stay closeted inside,” she says.

Types of light with the worst effect

“We have special receptors in our eyes which are connected to our biological clock. These receptors in our eyes have a maximum sensitivity to light of the blue spectrum. Hence light from our devices (smartphones, tablets, laptops, TV) which is highly enriched in the blue spectrum (it helps contrast with the light of day) is going to have the largest effect,” she explains. 

Scheuermaier says this is why it’s recommended that people do not use devices in the evening before going to sleep. And if they have to, they use the orange filters which exist on most devices these days.

“Those orange filters help somewhat as they do block the blue light but the brightness is still too high and still has an effect on our sleep-wake cycle,” she says.

Best conditions for quality sleep

Scheuermaier recommends that people have regular bedtimes and wake times.

“Leave time for sleep: about eight hours everyday. You won’t regret it as you will be more productive at work or school, feel better, and have better health.”

“Some people are helped by meditating before bedtime – to change the mood and get into a true sleepy mood/ non alert mood,” she says.

“The main thing is to avoid bright lights inside the house (neon lights for example), have a dim lit house two hours before bedtime, so we can allow our melatonin – a hormone that regulates the sleep-wake cycle – to rise and help make us sleepy, and avoid being on our devices. Rather read, do meditation, chat with family members or friends,” says Scheuermaier. – Health-e News


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