You probably heard that being exposed to Blue Light in the evening can affect your sleep negatively.

Recommendation for a good sleep is to avoid Blue light, especially screens, up to 2h before your bedtime.

This posts concentrate on 2 different effects Blue Light has on our sleep. On the one hand, it can deregulate our circadian clock, which make us go to bed later, and on the other hand it affects our melatonin production, the hormone that put us to sleep.

Blue light impact both our melatonin production and our circadian clocks

Effect on our Circadian clock

Basically, we have light sensitive cells at the back of our eyes (ipRGCs) which fire responses to any light (especially blue part of the spectrum) and send signals to areas of the brain that control alertness.

A research showed that an hour exposure to low intensity blue light increased people reaction speed more than 2 cups of coffee.

It also send signals to a part of the brain  (SCN) which is part of the body master clock, and can tweak the timing of our circadian clocks. So exposure to light in evening delays the timing of the SCN, making you go to bed later. 

Exposure to light in evening delays the timing of the SCN, making you go to bed later

Effect on melatonin

I finally found some data, based on a research carried out by Mariana Figueiro and her team at the Rensselaer polytechnic Institute of New York State (courtesy of article in the New Scientist).  The tested the impact of various blue lights (at various intensity) by measuring melatonin, a hormone linked to sleep that rises in the evening in response to a signal from your body clock. 

Figueiro’s team found that only bigger devices produce enough bluish-white light to affect your levels of melatonin

  • for adult, it was 85lux for 1h
  • for adolescents, 71 lux

A larger ipad can produce that amount of light, but iphone typically don’t. 

However, they found that lower intensities could suppress melatonin if people were exposed to them for longer period of time. Even night shift mode, which reduces the blue light on ipad, could still suppress melatonin.

In other word, her only advice is: turn it off, or use blue light glasses. 

TV screen at more than 2m is ok.

Typical levels of light in living rooms are ok. Key is how close is the light from you. Use warmer color light is recommended

There is also growing evidence that blue light could damage our vision by harming your retina overtime, though more research is needed ~ Source: BusinessInsider

What can you do?

Turn on Blue Light Mode

Most phones and laptop have functions to turn down the blue light. Not 100% reliable but better than nothing.

Use Blue Light glasses.

I don’;t have some as I don;t think I sufgfer from it, might get some in the winter

Turn down your light in the evening

Try to have light that is warmer color in your bedroom … may be use a dimmer light switch. I have Hue lights, so I can turn the intensity down in the evening and turn it back on in the morning automatically.