Even candlelight before bed is bright enough to delay sleep as scientist admits he keep his lights ‘as dim as possible without bumping into furniture’
- People’s individual sensitivity to light could be an important health factor
- Exposure to artificial light after sunset delays a rise in sleep hormone melatonin
- Some people are so sensitive only candlelight is enough to keep them awake
- While others don’t experience the same effect until they see sunrise brightness
Just the glow from a few candles could be enough to keep people up at night, according to research.
Bright lights can slow down the body’s production of melatonin, a hormone which spikes in the evening and makes us sleepy.
And while sleep experts often drill home advice against using phones, computers or TV before bed, even lower levels of light could be enough to disrupt sleep.
Researchers studying how different levels of light affected people found some people’s tolerance may be up to 58 times higher than others’.
One scientist involved in the study even admitted he keeps his home ‘as dim as I can without bumping into furniture’.
Researchers in Australia tested the effects of artificial light on people’s sleep patterns and found some people could withstand 60 times as much light as others before it impacted their ability to doze off (stock image)
Scientists at Monash University tested the effects of artificial light in the evening on a group of 55 men and women.
They found a level of light too low to read in – measured as 24.6 lux (lux are equal to a lumen per square metre) – was enough to stunt melatonin by 50 per cent in the average person.
However, some people experienced the same drop in light levels only a quarter as strong (six lux), which were equal to a few candles or half as bright as a streetlight.
Melatonin is a hormone which controls how asleep or awake people feel.
The hormone is produced in the pineal gland in the brain and its release into the body is controlled by light.
During the day, when the eye absorbs light, melatonin levels in the body are low and, as a result, we feel awake.
But when darkness settles and the amount of light being absorbed by the eye reduces (although this is disrupted in modern societies because of artificial light), more melatonin circulates round the body.
Melatonin prepares the body for sleep by slowing the heart rate, reducing blood pressure, and changing how heat is stored in the body – the body’s core temperature drops while the outside of the body and the limbs become warmer.
The hormone also makes people feel sleepy.
Melatonin supplements can be taken to aid sleep in people who have problems with it, as well as for certain medical conditions such as tinnitus or Alzheimer’s disease.
Sources: Medical News Today and Journal of Applied Physics
At the same time, those with a higher tolerance didn’t have the 50 per cent drop in their melatonin levels unless exposed to 350 lux, about the brightness of a sunrise.
‘For some people, a dim reading light might as well be daylight, and for others it might as well be darkness,’ associate professor Sean Cain told the New Scientist.
While people won’t be able to test their own light sensitivity, Professor Cain said it would be best to ‘err on the side of caution’.
He added: ‘I keep my lights as dim as I can without bumping into furniture.’
The intensity of a light appeared to have a direct effect on how long it delayed a rise in melatonin, which would influence how much longer sleep took to come.
A brightness of 10 lux, about equal to a streetlamp, could delay sleep by 22 minutes, the research found.
While 30 lux, the lowest light recommended for reading, led to a 77 minute delay, and 50 lux, equal to about a 45-watt lightbulb, added 109 minutes.
Professor Cain and his colleagues said how sensitive people are to light could be an underappreciated measure of how the body clock influences overall health.
In the research the group of 55 people followed a strict sleep pattern for up to eight weeks and were exposed to light and measured for one night per week in a lab.
The research was published in the journal PNAS.
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