Kiwis increased exposure to artificial blue light at night is knocking our body clocks out of kilter and may be putting our health at risk, says a Royal Society Te Apārangi report.

The paper Blue Light Aotearoa summarises the latest research evidence on the health impacts of exposure to artificial blue light from screens and lighting, as well as the impact on animals and astronomers’ ability to study the night sky.

Blue light is part of daylight which is made up of the whole ’rainbow’ spectrum of visible light. But blue light in particular triggers our natural circadian rhythms.  Scientists in 2002 discovered a new type of cell in the human eye that detects blue light and sends signals to the master circadian clock that not only governs our day/night body rhythms but a whole range of processes that influence our metabolism, immune function, sleep and mood.

Dr Lora Wu, Senior Research Officer at Massey University’s Sleep/Wake Research Centre and a contributor to the report, says people need to be exposed to natural blue light in the morning to keep their body clocks in synch.  But if our eyes’ blue-light sensitive cells perceive too much blue light at night then our bodies receive the wrong message and our body clocks are put ‘out-of-whack’ in a similar manner to jetlag.

“This not only disrupts our sleep but can have a range of negative flow-on effects to our health, such as increased risk of obesity, depression and potentially some types of cancer,” said Wu. “New evidence for health problems caused from disrupted sleep is emerging all the time.”

Preliminary evidence suggests that high levels of light exposure at night, particularly when enriched in blue wavelengths, may contribute to the development of some cancers and other health problems. Possible mechanisms proposed include sleep and circadian disruption due to suppression of the normal night-time production of melatonin or disruption of the immune system.

Associate professor Guy Warman, a chronobiology researcher at the University of Auckland, said the Society’s report was “both timely and important, particularly given the modern move to artificial light sources which produce ‘bluer’ light than we have previously been exposed to (such as LED lights in the home and public places, and blue light produced by electronic devices)”.

“The negative and positive effects of light in the blue end of the spectrum is an extremely important issue for scientists, policy makers and the general public alike,” he said.  The effects of blue light on our biology were relatively new and areas needing further research included how much artificial light exposure we’re getting in our everyday lives and when, said Warman.

The Society report says our increasingly 24/7 lifestyle alters our patterns of blue light exposure. Exposure to blue wavelengths in the evening, including from domestic lighting and light emitting screens, directly challenges our circadian drive for sleep at night by delaying the circadian clock.  Whereas reinforcing circadian rhythms with blue-enriched white light at the right time in the circadian cycle – i.e. in the morning – can improve alertness, performance, mood and sleep quality.  Also exposure to bright daylight may also reduce the sensitivity of the circadian system to blue light exposure at night compared to those experiencing dim daytime light with minimal outdoor light contact.

Wu said the health message can be summed up with the ditty:

Blue light at night, not so bright,

 Blue light in the morning, stops you yawning…’

Wu said the best way of receiving blue light in the morning was by being outside or via strong natural light coming in through a window.

“But, at the other end of the day, we need to limit how much blue light we are exposed to so as to not disrupt our sleep cycle and the many other factors of metabolism that are associated with our body clock, like digestion and cell renewal.”

Rather than sitting in the dark, there are practical things we can do to reduce our exposure to blue light at night, Dr Wu says.

“Inside our homes we can replace bluer ‘cooler’ light bulbs to bulbs that emit more yellow ‘warm’ light and use dimmers.

“We can also use software that reduces bright blue light from our digital screens at night or turn them off. It’s also important to make sure your bedroom is dark while you sleep, so unplug any ‘glowing’ devices and use good quality curtains.”

The Society’s report says repeated flashes of saturated blue light during the night, even

delivered through closed eyelids, has been shown to shift the human circadian clock.

Tips to reduce harmful effects on yourself

  • Be exposed to daylight in the morning and darkness at night for better circadian health and wellbeing.
  • Limit blue light exposure from digital screens including smartphones, televisions and computers at night by reducing screen brightness, using night-time apps that lower blue light output or turning devices off.
  • Replace brighter blueish ‘cool-white’ lightbulbs with warmer-coloured, yellowish ‘warm-white’ lightbulbs.


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