Is blue light a red herring?

Is blue light a red herring?

I've just returned from the latest excellent Talk About Trust's 2025 conference in Bournemouth, where someone mentioned the dire effects of blue light from smartphones on the sleep patterns of teenagers. This is widely talked about and may be something of a core belief in our community (1), but is it really something to worry about?
The story is that a surge of secretion by the pineal gland of a hormone, melatonin, promotes sleepiness at night, and blue light from our devices suppresses or delays that surge.
A widely-cited study from 2014(2) showed that use of an e-reader in a dimly lit room delayed sleep by 10 minutes, and did so by reducing melatonin levels. The authors pointed the finger at the shorter wavelengths of light in particular -- the blue end of the spectrum.
These suggested effects of our devices has spawned a whole industry of apps and filters designed to reduce the exposure of our eyes to such blue light.
Yet...
10 minutes' delay in getting to sleep is unwelcome, but if that's the worst night's sleep I ever had, I would count myself very lucky.
Also, the study used as its exposure condition, 4 hours of reading on a device set to maximum brightness in a dimly lit room. If I wanted to show an effect, that's what I would do too, but that's not a real-world case. My 'phone automatically dims itself in a dim room, so at most I can be getting only a fraction of the blue light from my device than the participants in that study.
In fact, “The evidence for smartphone use near bedtime affecting sleep and circadian rhythms isn’t great,” says Professor Stuart Peirson, a professor of circadian neuroscience at Oxford University.(3)(4)
I'm much more concerned about what screens are showing than how blue they are, how exciting or upsetting is that content, whether teenagers are using phones when they should be asleep, and whether their phones are set to 'do not disturb' at night, and... The blue light story may be an unimportant distraction.
The bigger story about teenagers and sleep cycles is that we have persisted in making them get up and go to school at a time which does not fit their sleep cycle at all, and this has been going on long before anyone had heard of a smartphone.(5)
(1) https://kidshealth.org/en/teens/blue-light.html
(2) https://www.pnas.org/doi/10.1073/pnas.1418490112
(3) https://www.wired.com/story/blue-light-smartphone-screen-sleep/
(4) https://www.sciencedirect.com/science/article/pii/S1087079224000376
(5) https://sheu.org.uk/sheux/EH/eh303ed2.pdf

Topics: 
lifestyle
research
Author: 
DrDave
Post date: 
23 June 2025 11:13