Blue light: do cell phones and the like really disturb sleep?

Christiane Fux studied journalism and psychology in Hamburg. The experienced medical editor has been writing magazine articles, news and factual texts on all conceivable health topics since 2001. In addition to her work for, Christiane Fux is also active in prose. Her first crime novel was published in 2012, and she also writes, designs and publishes her own crime plays.

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Widespread advice is that if you sleep poorly, you shouldn't stare at displays in the evening. The blue light that they emit is said to make it difficult to fall asleep. But is that really true?

It is correct: blue light is a pick-me-up. It is contained in a larger proportion in daylight. If the reddish part of the light spectrum increases towards evening, the body produces more of the "sleep hormone" melatonin.

The connection between the use of digital media and sleep disorders seems obvious. But it has not been proven. It seems questionable whether the blue light waves emitted by LED screens are even sufficient for such an effect.

For example, while an overcast winter sky still shines at 5000 lux on the eye retina, even modern mobile spays only manage a fraction of it.

Night light mode doesn't help

In fact, the number of studies so far has been fairly thin, and the test groups are rather small. A new study can now come up with at least 167 study participants. Before going to sleep, the 18 to 24 year olds used an iPhone either with or without special evening lighting (“Night Shift”) for the display with a warmer light spectrum. Another group avoided cell phones and other electronic media at all before going to bed.

The subjects' sleep quality and duration were then monitored the following night. The participants also wore chest straps with devices to monitor their heart rate. The result: none of the groups slept better or worse than the others.

This is matched by the results of another study: There researchers had shown that the night shift mode did not increase the amount of melatonin released.

Lights dim in the evening

Dimming the lights in the evening can still make sense: unlike the color of the light, the intensity of the radiation actually has an effect on melatonin production. Researchers at Monash University in Melbourne have shown that this is halved on average even with the usual evening lighting in households.

"Anyone who wants to read on an electronic device before going to sleep should avoid maximum brightness - this recommendation sounds trivial, but it is correct," reports Prof. Michael Bach from the Freiburg University Medical Center in a press release from the German Ophthalmological Society.

Reactions to light are individually different

What is particularly exciting about the study mentioned: the influence of the amount of light on the release of the sleep hormone turned out to be very different from one individual to the next. While with some test persons the amount of melatonin only halved in very bright light, with others an amount of light that corresponded to a candle flame was sufficient. “The effects of lighting on a certain person are highly unpredictable,” write the researchers working with Sean W. Cain.

And that corresponds to everyday experience: some people slumber easily in any situation, others even small disruptive factors bring about sleep. In addition to external factors such as light and noise, heavy food, exercise in the evening or caffeine consumption, psychological disruptive elements in particular can play a role here.

“Lights off” also means “mobile phone off!

And this is where mobile phone use comes into play again: A study at the School for Mass Communication Research in Leuven, Belgium showed that those of the 844 participants who still use their mobile phone after the light was turned off slept worse and were more tired the next day.

Sleep researchers recommend sleep disturbed people to mentally calibrate themselves to bedtime: with relaxing evening routines and rather calm mental activities. If you use your cell phone in bed, you don't shut it down mentally - and that can be the real sleep-thief.

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