Jen Oliver: Welcome to the, so that's Why podcast where we unpack the
science behind everyday questions.
I'm Jen.
Chris Smith: I'm Chris.
Matt Edmundson: And I'm Matt.
Jen Oliver: Right.
Today we're answering something that affects everyone with a smartphone,
laptop, or tablet, which is basically.
All of us.
Why does blue light affect sleep?
Because we've all heard we shouldn't scroll through our phones before bed,
but has anyone actually explained why?
Matt Edmundson: So you are talking, Jen, about this nightly ritual of lying
in bed, promising yourself just five more minutes of scrolling and then
suddenly realizing an hour's gone by.
And you've watched 17 videos of cats being scared by cucumbers.
Jen Oliver: Exactly.
I'm guilty of it, I have to admit.
Matt Edmundson: Yeah, me too.
Jen Oliver: Maybe not the cats and cucumbers, but hey.
Matt Edmundson: No, no, definitely those as well.
Jen Oliver: But here's what's fascinating.
For most of human history, the only blue light we encountered after
sunset was moonlight or starlight.
Now we're bathing our eyeballs in it.
Rife right up until we try and sleep.
Chris Smith: And so hopefully by the end of this episode we'll have explained
why your brain interprets that phone screen as a tiny artificial sunrise.
How specialized cells in your eyes communicate directly with your
internal clock and why children are significantly more vulnerable
to these effects than adults.
Matt Edmundson: Plus, we are tackling whether those trendy blue light blocking
glasses actually work or if they're just expensive fashion accessories.
Chris Smith: So.
Let's start with why this matters, and research shows that using an LED
backlit device for just two hours before bed can suppress melatonin production
by over 50% and delay when melatonin starts rising by an hour and a half.
The reason that's significant is when you consider that melatonin is your
body's signal that it's time to wind down
Jen Oliver: and the knock on effects are substantial.
Studies found that around a third of people experience reduced sleep duration
with evening blue light exposure, and half of those report feeling less tired
at bedtime, which sounds positive until you realize it means your body's natural
drowsiness signals are being overridden.
Matt Edmundson: So, so then Jen, all those times I've thought, I'm not tired yet.
I'll just watch one more episode.
My phone apparently is lying to me.
At least that's how I'm interpreting it.
Uh, and so we'll feel betrayed by my own technology.
Mm-hmm.
Chris Smith: That technology betrays in the end.
It's all I've seen that I've seen that movie.
It always does.
Matt Edmundson: It gets you in the end.
Chris Smith: Um, what's particularly concerning is research
showing that pre-B bedtime.
Blue lights exposure can reduce the proportion of deep
sleep throughout the night.
And of course, deep sleep is when your body does its most
important restorative work.
Jen Oliver: Yeah, I mean, we covered in our sleep episode how critical those
deep sleep stages are for things like your memory consolidation, physical
restoration, so disrupting them, it's got consequences well beyond
just feeling groggy in the morning.
Matt Edmundson: Okay, chaps.
So what actually happens biologically?
How does, uh, the blue light from the screen mess with my sleep?
Chris Smith: The key players here are specialized cells in your retina.
Yeah,
Matt Edmundson: so, let me guess, Chris Wright, they've got a
name that I have absolutely no chance of pronouncing whatsoever.
Chris Smith: I knew you'd do this to me.
They are called intrinsically photosensitive retinal ganglion cells.
Matt Edmundson: So yes is the answer to the
question,
Chris Smith: but for today, we'll call them IP RGCs in short.
So these IPRGCs don't contribute much to vision at all.
But they detect ambient light levels and send that information to your brain
and effectively to its master clock.
Jen Oliver: And these cells also contain a light sensitive protein called melanopsin.
And here's the crucial bit.
Melanopsin is most sensitive to blue light wavelengths, specifically
between 460 and 480 nanometers.
And that happens to overlap significantly with the light emitted by our screens.
Matt Edmundson: What a surprise.
Jen Oliver: What a surprise.
Matt Edmundson: I
have no idea what an nanometer is, but what a surprise.
So we've basically got specialized blue light detectors in our eyes that
aren't designed for a Netflix binge.
That's what you're telling me, right?
Chris Smith: Yep, exactly right.
And when Blue Light hits these melanopsin containing cells,
they find signals along a pathway directly to the Supra charismatic
nucleus, which we'll call the SCN.
Jen Oliver: I love that.
Chris Smith: Now this, I
Matt Edmundson: wanna be super charismatic.
Jen Oliver: We've got one,
we've each got one.
Chris Smith: And this SCN, I'm not gonna try and say it again.
Um, it sits in your hypothalamus in the brain.
But if you think of the SCN as your body's central timekeeper, it's coordinating
your 24 hour circadian rhythm.
Jen Oliver: And when the SCN receives these signals saying bright blue light
detected, it interprets this as daytime.
So in response, it sends inhibitory signals that suppress melatonin
in production in the pineal gland.
Matt Edmundson: So my brain then is literally thinking the phone is the sun.
Jen Oliver: Yeah.
Matt Edmundson: Is that
right?
Chris Smith: Yeah.
At a biological level, I'd say yes.
So your circadian systems can't distinguish between natural daylight
and artificial light from screens 'cause both activate the same
pathway under normal circumstances.
As evening approaches and blue light exposure decreases, the pineal gland in
your brain starts producing melatonin about two hours before your usual bedtime.
This rising melatonin signals that your body, that sleep is coming.
Jen Oliver: But when you're exposed to blue light in those evening
hours, this melatonin, the normal rise, it gets suppressed or delayed.
And research has shown that this follows what scientists call
a dose response relationship.
Brighter blue light produces greater melatonin.
Matt Edmundson: So I, I'm, listen, I'm, I'm, I, I had no idea my
casual scrolling was having such a measurable biological impact.
Jen Oliver: I know.
And what makes this particularly relevant to modern life is that blue
lights affects a wavelength specific.
Chris Smith: And interestingly, but probably not surprisingly, the
effects don't disappear immediately when you turn off the screen.
So this suppression of melatonin and the alerting effects can persist for some
time after that light source is removed.
So your circadian system doesn't have an instant reset button, for instance.
Matt Edmundson: So if I. Even.
Even if I sort of put my phone down finally and say at midnight, the damage
is already done for that evening.
Is that what you're saying?
Jen Oliver: To some extent, yes.
So the melatonin delay has already been triggered and this is why recommendations,
fo recommendations focus on like limiting blue light exposure in the hours
before bed, not just at bedtime itself.
Chris Smith: And something that's really interesting for parents to know is
that children are significantly more sensitive to these effects than adults.
So sorry kids, but it's true.
But
Matt Edmundson: sensitive, how, what does that mean?
Jen Oliver: Well, a study comparing children with an average age, age
of about nine to adults around the age of 40, they, it found striking
differences between the two.
So under blue light and enriched lighting conditions, children experience over
80% reduction in melatonin levels.
But adults showed much weaker responses to the same light.
Chris Smith: That's it.
And, um, there are several factors that explain this.
So firstly, children have larger pupils than adults and, and that allows
more light into the eye, but also their crystal eye lenses are clearer.
Yeah, as we age and get a bit more jaded, our lens is naturally yellow,
and this actually filters out some blue light, whereas children's lenses
transmit a high proportion of blue light to those photosensitive cells.
Matt Edmundson: So the very thing that gives kids those beautiful
crystal clear eyes also makes them more vulnerable to the screen.
Which is ironic, isn't it?
Every parent trying to pry an iPad away at bedtime.
Good news is you've now got scientific backing which your children will
fully understand and agree with.
Chris Smith: Yeah, yeah.
Good luck with that.
Jen Oliver: Yeah, no they won't.
But children, they also naturally produce melatonin earlier in the evening.
And in higher amounts than adults, which may make the suppressive
effects more pronounced.
And then the heightened sensitivity is particularly concerning given how
common device use has become before bed.
Chris Smith: Yeah.
And at the other end of the.
Kind of age spectrum.
Older adults may be somewhat less vulnerable because of that lens, uh,
yellowing that I mentioned earlier.
But however, this reduced blue light transmission can actually contribute
to weaker circadian rhythms and the sleep problems common in elderly people.
Jen Oliver: It is worth noting that individual sensitivity
varies quite a bit too.
Some people seem to tolerate evening use with minimal sleep disruption, whereas
others are highly sensitive and there's also genetic variations in clock genes
and differences in melanopsin sensitivity, and they all contribute to this variation.
Matt Edmundson: So some people think.
Really can get away with scrolling before bed whilst others can't,
which hardly seems fair to me.
If I can't and
Jen Oliver: life's not fair,
Matt Edmundson: get over it
Chris Smith: and, and research backs that unfairness.
So research has shown that under identical like conditions, some people experience
near complete melatonin suppression while others show minimal effects.
So if you've noticed that evening screen use doesn't seem to affect
your sleep, you may be less sensitive.
But if you're struggling to sleep.
And, and actually get off to sleep in that, that onset limiting evening
blue light is definitely worth trying.
Matt Edmundson: Mm. Okay.
So what about then guys, the blue light blocking glasses.
I see them everywhere.
Do they actually work?
Should I buy them?
Chris Smith: Yeah, it's an interesting one.
And the research here shows mixed results, but actually on the promising side.
So there's certain studies of involving people with insomnia
have found that wearing am tinted lenses for two hours before bedtime.
Did lead to improvements in sleep quality and duration compared to clear lenses.
Jen Oliver: And the key word there is amber tinted.
So blue light blocking glasses vary enormously in their effectiveness.
Some clear blue blockers filter only about 10 to 30% of blue light,
whereas amber or orange lenses can actually block 90% or more.
The darker tins that block more light tend to show more
consistent benefits in the studies.
Matt Edmundson: Well, I've got some amber tinted ski goggles I could wear to bed.
That might, that might be worth it.
Jen Oliver: Yeah.
I wanna see a photo that, yeah, reading your book with your
ski goggles on or watching
Matt Edmundson: Yep.
Doing that.
Jen Oliver: Looking at your phone.
Chris Smith: I don't want, I don't wanna see a photo.
Um, but you know, for those who can't avoid like evening screen
use, uh, am tin glasses used two to three hours before bed may help.
So it's definitely worth a, a go, but it's not a complete solution
because it's the stimulating content.
Itself.
You know, scrolling social media, catch up on work, emails, watching exciting
shows or boring shows, they all activate our brains regardless of wavelength.
So they all contribute.
Matt Edmundson: Which is fair enough.
Yeah, I get that.
So what about, um, night mode then on phones?
Jen Oliver: Well, research is interesting.
There was a study in 2024 that suggested that overall screen
brightness might matter as much as, or more than the color of light.
So night mode combined with reduced brightness appears more
effective than either alone.
Matt Edmundson: That's interesting, isn't it?
So turning on the night mode, but keeping the brightness like at maximum.
Seems to be like self-defeating, isn't it?
Mm. So, Chris, practical recommendations, you've bound to
have got some, but what are they?
Chris Smith: Yeah, A few things.
I think dimming your screens and, and using warmer color
settings in the evening.
Worth a try.
Considering am tinted glasses, if you must use, uh, devices before bed,
and ideally establishing a consistent time, say two hours before sleep when
you set devices aside altogether.
Jen Oliver: So one thing we should address.
Um, is the persistent myth that blue light from screens damages your
eyes And it's important to note that current evidence doesn't support this,
Matt Edmundson: which is interesting, isn't it?
'cause I, there's a lot of marketing hype out there and I know we're,
we're, you know, we are always down on marketing hype, but there is a lot of
marketing hype out there about protecting your eyes from the harmful blue.
Chris Smith: Yeah, you can get blue light treatment so it can get blue
light well, protection from blue light.
So it's a, it's a complete kind of hypocrisy.
And the confusion comes from laboratory studies using extremely high intensity
blue light on isolated cells.
But the thing is, screens emit far less blue light than natural sunlight does.
The sun delivers up to 1000 times more blue light.
Than you'd get from your electronic device.
So if a screen blue light was genuinely harmful to our retinas, outdoor
sunlight would be catastrophic.
Yeah.
Our eyes, of course, can handle daylight fine.
Jen Oliver: In the American Academy of Ophthalmology, they stated that there's
insufficient evidence that blue light from devices damages eyes, what screens
do, cause its digital eye strain, dry eyes, fatigue, headaches, but that's
from prolonged screen use and reduce blinking, not the blue light itself.
Matt Edmundson: That's interesting, Jen.
So any more recommendations, Chris?
Chris Smith: Yeah, so there are some simple environmental
changes that can help too.
So, switching to warm colored, dim lighting in the evening or bulbs
with, uh, lower color temperatures.
That reduces blue light exposure without requiring glasses or screen changes.
Jen Oliver: Yeah, and don't over overlook the power of getting
bright light during the day.
So getting outside for natural daylight, especially in the morning, that
actually strengthens your circadian rhythms, and so it might reduce your
sensitivity to evening light disruption.
It's not just about avoiding blue light at night.
It's about getting enough at the right times.
Matt Edmundson: So morning sunlight then is my friend, if I understand it.
But late night phone scrolling is perhaps a frenemy.
I just like that word frenemy.
Had to get it in.
Chris Smith: That's, it's a bit too Gen Z for me.
Jen Oliver: We're done with the kids
Matt Edmundson: Z or Gen Z.
Jen Oliver: It's okay.
Matt Edmundson: I
dunno,
Chris Smith: I dunno
which generation we're in these days.
Alpha, beta, I, I dunno.
Um, but no, you, you're right.
I mean the real concern here with blue, blue light is.
The, uh, circadian disruption rather than eye damage itself.
And this connects to everything else we've discussed on this podcast.
So sleep quality affects cognitive function, mood, metabolism,
immune function, everything.
Jen Oliver: And the circadian system also influences when we
feel hungry, when we have energy, and when hormones are released.
So disrupting it with mistimed light exposure can have ripple
effects throughout your biology.
Chris Smith: The good news.
If there is some good news is that blue light exposure during
the day is actually beneficial.
It promotes alertness and it helps reinforce strong circadian rhythms.
As Jen was saying, it's specifically the evening exposure that causes these
problems that we're talking about.
Matt Edmundson: Yeah, and listening to you guys talk, I'm realizing maybe just
five more minutes of scrolling might be costing me more than I thought.
So not just lost sleep, but lower quality of sleep when I do finally drop off.
Jen Oliver: So why does blue light affect sleep?
Chris Smith: Blue light affects sleep because specialized cells in your
retina containing melanopsin are highly sensitive to blue wavelengths.
When these cells detect blue light, they signal to your brain's master clock
that it's daytime, which suppresses melatonin production and delays your
body's natural wind down process.
Matt Edmundson: So every time I check my phone at 11:00 PM my brain genuinely
thinks I've glimpsed the sunrise.
And I wonder, I can't sleep after a scrolling session.
Jen Oliver: Now you know why dimming your screens using warmer light settings
and ideally putting devices away a couple of hours before bed can make
such a difference to sleep quality.
Your circadian system simply can't tell the difference between
your phone and the morning sun.
That's it for this week.
Make sure you hit that subscribe button.
We're unpacking the science behind everyday questions each week.
Tell us in the comments what you'd like us to explore.
Thanks for geeking out with us, but for now, that's it from me.
Matt Edmundson: That's it from me,
Chris Smith: and that's it from me.
Jen Oliver: Bye for now.