You often read that light in the evening keeps you awake and that blue light is mainly the culprit. Questions like ‘how many hours before bedtime without blue light?’ and ‘what does blue light do to your brain?’ are therefore regularly asked. Blue light is also said to have a negative effect on your melatonin production. But what is it really like? Sleep scientist Merijn van de Laar, knowledge partner of Beter Bed, tells you all about it.
Blue light for sleeping, very normal these days
It’s the most normal thing in the world: after dinner you flop on the couch. Watch some TV before going to bed. When your favorite movie or series is over, you move to your bed to check all the social media on your phone. You spend the entire evening with screens and that means a lot of blue light before sleeping.
Does blue light before sleeping have a negative effect?
Blue light and sleep, what do they have to do with each other? First of all, it is good to know that almost all (ambient) light has an effect on sleep. The strength of the light is especially important. We express this in lux. To give you an idea of light intensity: daylight, for example, is approximately 10,000 lux, while a well-lit office sometimes only just reaches 500 lux. The light intensity (the number of lux) you are in has more effect on your sleep quality than the light color.
Is it good to filter out blue light with glasses?
Many studies have been done on blue light and sleep quality, but most studies are not well designed. One study found small effects of blue light filter glasses on sleep, while the other did not. A recent large study shows that the effect of glasses on sleep quality has not been properly demonstrated so far.
Some glasses seem to filter out more blue light than others, but the effect of orange, well-sealed glasses on sleep quality also seems to be limited. Young people who wear orange glasses before sleeping may have slightly better sleep quality, but the difference is very small.
Does it make sense to limit blue light before going to sleep?
So it actually doesn’t matter much whether it is blue light or other light. Too much light before bedtime has a negative effect on sleep. It is therefore not surprising that (solely) filtering out blue light seems to have so little effect on sleep quality. It turns out that light of other wavelengths can also lead to changes in your sleep. In general, it can be said that it is not so much the color, but rather the amount of light, and especially the ambient light, that is important for your sleep quality.
How much ambient light do you need at what times?
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In the morning and during the day
Timing of light is important. A study from the Netherlands shows that later exposure to a small amount of light in the morning is associated with waking up more often and staying awake for longer. So getting yourself into the light early in the morning seems like a good idea, because it may help you sleep better the next night.
If you are mainly exposed to artificial (and probably warmer and weaker) light during the day, you appear to be more sensitive to the negative effects of light in the evening. If you have been outside a lot during the day, you are better protected against evening light and you sleep better. In other words: a walk outside in the daylight can have a positive effect on your sleep*.
*Small side note: in this study it is that people who work more indoors may have less physical exercise and that this can play a role in the results. But don’t worry: if that were the case, walking (outside) would still be a good idea!
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‘in the evening
In the evening it is important to dim the light as much as possible. The less light you have had during the day, the more this can help. A light intensity of a maximum of 10 candles is recommended from 3 hours before you go to bed. That is comparable to twilight. In short: turn off those fluorescent lights early in the evening and use as little light as possible in the last hours before you go to bed.
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‘at night
Here applies; the darker the better. At night, extreme darkness is best. Even if you close your eyes, very dim light can affect your sleep.
How long before bed should I not use screens?
So it is not so much blue light that is the culprit when it comes to reduced sleep quality. It is important to ensure that you do not take in too much light too late. It is of course true that watching television and using (blue) screens before going to sleep does have an effect on stimuli. Are you watching Netflix and scrolling on your phone at the same time? Then you get much more stimulation than when you quietly read a book. And that amount of stimuli does have an effect on your sleep. Using as few screens as possible before going to bed is therefore not a bad idea. How do you arrange that? In any case, don’t look at screens an hour and a half before you go to sleep. Find a replacement activity that you can do in the evening, such as reading, a yoga flow or listening to music. And, super important: don’t put a TV in your bedroom, that’s bad for your night’s sleep anyway.
