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Why Does Blue Light Affect Sleep? · So That's Why

• 0:04
  Jen Oliver: Welcome to the, so that's Why podcast where we unpack the
• 0:08
  science behind everyday questions.
• 0:10
  I'm Jen.
• 0:11
  Chris Smith: I'm Chris.
• 0:12
  Matt Edmundson: And I'm Matt.
• 0:13
  Jen Oliver: Right.
• 0:13
  Today we're answering something that affects everyone with a smartphone,
• 0:17
  laptop, or tablet, which is basically.
• 0:20
  All of us.
• 0:21
  Why does blue light affect sleep?
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  Because we've all heard we shouldn't scroll through our phones before bed,
• 0:28
  but has anyone actually explained why?
• 0:31
  Matt Edmundson: So you are talking, Jen, about this nightly ritual of lying
• 0:35
  in bed, promising yourself just five more minutes of scrolling and then
• 0:39
  suddenly realizing an hour's gone by.
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  And you've watched 17 videos of cats being scared by cucumbers.
• 0:48
  Jen Oliver: Exactly.
• 0:49
  I'm guilty of it, I have to admit.
• 0:51
  Matt Edmundson: Yeah, me too.
• 0:52
  Jen Oliver: Maybe not the cats and cucumbers, but hey.
• 0:54
  Matt Edmundson: No, no, definitely those as well.
• 0:57
  Jen Oliver: But here's what's fascinating.
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  For most of human history, the only blue light we encountered after
• 1:03
  sunset was moonlight or starlight.
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  Now we're bathing our eyeballs in it.
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  Rife right up until we try and sleep.
• 1:11
  Chris Smith: And so hopefully by the end of this episode we'll have explained
• 1:13
  why your brain interprets that phone screen as a tiny artificial sunrise.
• 1:19
  How specialized cells in your eyes communicate directly with your
• 1:22
  internal clock and why children are significantly more vulnerable
• 1:26
  to these effects than adults.
• 1:28
  Matt Edmundson: Plus, we are tackling whether those trendy blue light blocking
• 1:33
  glasses actually work or if they're just expensive fashion accessories.
• 1:37
  Chris Smith: So.
• 1:38
  Let's start with why this matters, and research shows that using an LED
• 1:43
  backlit device for just two hours before bed can suppress melatonin production
• 1:48
  by over 50% and delay when melatonin starts rising by an hour and a half.
• 1:53
  The reason that's significant is when you consider that melatonin is your
• 1:57
  body's signal that it's time to wind down
• 2:00
  Jen Oliver: and the knock on effects are substantial.
• 2:03
  Studies found that around a third of people experience reduced sleep duration
• 2:08
  with evening blue light exposure, and half of those report feeling less tired
• 2:13
  at bedtime, which sounds positive until you realize it means your body's natural
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  drowsiness signals are being overridden.
• 2:21
  Matt Edmundson: So, so then Jen, all those times I've thought, I'm not tired yet.
• 2:26
  I'll just watch one more episode.
• 2:29
  My phone apparently is lying to me.
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  At least that's how I'm interpreting it.
• 2:33
  Uh, and so we'll feel betrayed by my own technology.
• 2:36
  Mm-hmm.
• 2:37
  Chris Smith: That technology betrays in the end.
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  It's all I've seen that I've seen that movie.
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  It always does.
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  Matt Edmundson: It gets you in the end.
• 2:43
  Chris Smith: Um, what's particularly concerning is research
• 2:46
  showing that pre-B bedtime.
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  Blue lights exposure can reduce the proportion of deep
• 2:51
  sleep throughout the night.
• 2:53
  And of course, deep sleep is when your body does its most
• 2:55
  important restorative work.
• 2:57
  Jen Oliver: Yeah, I mean, we covered in our sleep episode how critical those
• 3:01
  deep sleep stages are for things like your memory consolidation, physical
• 3:06
  restoration, so disrupting them, it's got consequences well beyond
• 3:11
  just feeling groggy in the morning.
• 3:14
  Matt Edmundson: Okay, chaps.
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  So what actually happens biologically?
• 3:17
  How does, uh, the blue light from the screen mess with my sleep?
• 3:22
  Chris Smith: The key players here are specialized cells in your retina.
• 3:25
  Yeah,
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  Matt Edmundson: so, let me guess, Chris Wright, they've got a
• 3:27
  name that I have absolutely no chance of pronouncing whatsoever.
• 3:33
  Chris Smith: I knew you'd do this to me.
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  They are called intrinsically photosensitive retinal ganglion cells.
• 3:38
  Matt Edmundson: So yes is the answer to the
• 3:41
  question,
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  Chris Smith: but for today, we'll call them IP RGCs in short.
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  So these IPRGCs don't contribute much to vision at all.
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  But they detect ambient light levels and send that information to your brain
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  and effectively to its master clock.
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  Jen Oliver: And these cells also contain a light sensitive protein called melanopsin.
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  And here's the crucial bit.
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  Melanopsin is most sensitive to blue light wavelengths, specifically
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  between 460 and 480 nanometers.
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  And that happens to overlap significantly with the light emitted by our screens.
• 4:15
  Matt Edmundson: What a surprise.
• 4:16
  Jen Oliver: What a surprise.
• 4:17
  Matt Edmundson: I
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  have no idea what an nanometer is, but what a surprise.
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  So we've basically got specialized blue light detectors in our eyes that
• 4:24
  aren't designed for a Netflix binge.
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  That's what you're telling me, right?
• 4:28
  Chris Smith: Yep, exactly right.
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  And when Blue Light hits these melanopsin containing cells,
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  they find signals along a pathway directly to the Supra charismatic
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  nucleus, which we'll call the SCN.
• 4:40
  Jen Oliver: I love that.
• 4:40
  Chris Smith: Now this, I
• 4:41
  Matt Edmundson: wanna be super charismatic.
• 4:42
  Jen Oliver: We've got one,
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  we've each got one.
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  Chris Smith: And this SCN, I'm not gonna try and say it again.
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  Um, it sits in your hypothalamus in the brain.
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  But if you think of the SCN as your body's central timekeeper, it's coordinating
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  your 24 hour circadian rhythm.
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  Jen Oliver: And when the SCN receives these signals saying bright blue light
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  detected, it interprets this as daytime.
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  So in response, it sends inhibitory signals that suppress melatonin
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  in production in the pineal gland.
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  Matt Edmundson: So my brain then is literally thinking the phone is the sun.
• 5:19
  Jen Oliver: Yeah.
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  Matt Edmundson: Is that
• 5:20
  right?
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  Chris Smith: Yeah.
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  At a biological level, I'd say yes.
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  So your circadian systems can't distinguish between natural daylight
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  and artificial light from screens 'cause both activate the same
• 5:30
  pathway under normal circumstances.
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  As evening approaches and blue light exposure decreases, the pineal gland in
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  your brain starts producing melatonin about two hours before your usual bedtime.
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  This rising melatonin signals that your body, that sleep is coming.
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  Jen Oliver: But when you're exposed to blue light in those evening
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  hours, this melatonin, the normal rise, it gets suppressed or delayed.
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  And research has shown that this follows what scientists call
• 5:57
  a dose response relationship.
• 5:59
  Brighter blue light produces greater melatonin.
• 6:03
  Matt Edmundson: So I, I'm, listen, I'm, I'm, I, I had no idea my
• 6:07
  casual scrolling was having such a measurable biological impact.
• 6:10
  Jen Oliver: I know.
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  And what makes this particularly relevant to modern life is that blue
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  lights affects a wavelength specific.
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  Chris Smith: And interestingly, but probably not surprisingly, the
• 6:20
  effects don't disappear immediately when you turn off the screen.
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  So this suppression of melatonin and the alerting effects can persist for some
• 6:28
  time after that light source is removed.
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  So your circadian system doesn't have an instant reset button, for instance.
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  Matt Edmundson: So if I. Even.
• 6:36
  Even if I sort of put my phone down finally and say at midnight, the damage
• 6:39
  is already done for that evening.
• 6:40
  Is that what you're saying?
• 6:41
  Jen Oliver: To some extent, yes.
• 6:43
  So the melatonin delay has already been triggered and this is why recommendations,
• 6:47
  fo recommendations focus on like limiting blue light exposure in the hours
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  before bed, not just at bedtime itself.
• 6:55
  Chris Smith: And something that's really interesting for parents to know is
• 6:58
  that children are significantly more sensitive to these effects than adults.
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  So sorry kids, but it's true.
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  But
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  Matt Edmundson: sensitive, how, what does that mean?
• 7:07
  Jen Oliver: Well, a study comparing children with an average age, age
• 7:10
  of about nine to adults around the age of 40, they, it found striking
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  differences between the two.
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  So under blue light and enriched lighting conditions, children experience over
• 7:22
  80% reduction in melatonin levels.
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  But adults showed much weaker responses to the same light.
• 7:29
  Chris Smith: That's it.
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  And, um, there are several factors that explain this.
• 7:32
  So firstly, children have larger pupils than adults and, and that allows
• 7:36
  more light into the eye, but also their crystal eye lenses are clearer.
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  Yeah, as we age and get a bit more jaded, our lens is naturally yellow,
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  and this actually filters out some blue light, whereas children's lenses
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  transmit a high proportion of blue light to those photosensitive cells.
• 7:53
  Matt Edmundson: So the very thing that gives kids those beautiful
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  crystal clear eyes also makes them more vulnerable to the screen.
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  Which is ironic, isn't it?
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  Every parent trying to pry an iPad away at bedtime.
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  Good news is you've now got scientific backing which your children will
• 8:09
  fully understand and agree with.
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  Chris Smith: Yeah, yeah.
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  Good luck with that.
• 8:12
  Jen Oliver: Yeah, no they won't.
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  But children, they also naturally produce melatonin earlier in the evening.
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  And in higher amounts than adults, which may make the suppressive
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  effects more pronounced.
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  And then the heightened sensitivity is particularly concerning given how
• 8:28
  common device use has become before bed.
• 8:31
  Chris Smith: Yeah.
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  And at the other end of the.
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  Kind of age spectrum.
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  Older adults may be somewhat less vulnerable because of that lens, uh,
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  yellowing that I mentioned earlier.
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  But however, this reduced blue light transmission can actually contribute
• 8:43
  to weaker circadian rhythms and the sleep problems common in elderly people.
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  Jen Oliver: It is worth noting that individual sensitivity
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  varies quite a bit too.
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  Some people seem to tolerate evening use with minimal sleep disruption, whereas
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  others are highly sensitive and there's also genetic variations in clock genes
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  and differences in melanopsin sensitivity, and they all contribute to this variation.
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  Matt Edmundson: So some people think.
• 9:09
  Really can get away with scrolling before bed whilst others can't,
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  which hardly seems fair to me.
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  If I can't and
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  Jen Oliver: life's not fair,
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  Matt Edmundson: get over it
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  Chris Smith: and, and research backs that unfairness.
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  So research has shown that under identical like conditions, some people experience
• 9:27
  near complete melatonin suppression while others show minimal effects.
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  So if you've noticed that evening screen use doesn't seem to affect
• 9:35
  your sleep, you may be less sensitive.
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  But if you're struggling to sleep.
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  And, and actually get off to sleep in that, that onset limiting evening
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  blue light is definitely worth trying.
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  Matt Edmundson: Mm. Okay.
• 9:45
  So what about then guys, the blue light blocking glasses.
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  I see them everywhere.
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  Do they actually work?
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  Should I buy them?
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  Chris Smith: Yeah, it's an interesting one.
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  And the research here shows mixed results, but actually on the promising side.
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  So there's certain studies of involving people with insomnia
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  have found that wearing am tinted lenses for two hours before bedtime.
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  Did lead to improvements in sleep quality and duration compared to clear lenses.
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  Jen Oliver: And the key word there is amber tinted.
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  So blue light blocking glasses vary enormously in their effectiveness.
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  Some clear blue blockers filter only about 10 to 30% of blue light,
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  whereas amber or orange lenses can actually block 90% or more.
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  The darker tins that block more light tend to show more
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  consistent benefits in the studies.
• 10:34
  Matt Edmundson: Well, I've got some amber tinted ski goggles I could wear to bed.
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  That might, that might be worth it.
• 10:38
  Jen Oliver: Yeah.
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  I wanna see a photo that, yeah, reading your book with your
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  ski goggles on or watching
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  Matt Edmundson: Yep.
• 10:44
  Doing that.
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  Jen Oliver: Looking at your phone.
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  Chris Smith: I don't want, I don't wanna see a photo.
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  Um, but you know, for those who can't avoid like evening screen
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  use, uh, am tin glasses used two to three hours before bed may help.
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  So it's definitely worth a, a go, but it's not a complete solution
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  because it's the stimulating content.
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  Itself.
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  You know, scrolling social media, catch up on work, emails, watching exciting
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  shows or boring shows, they all activate our brains regardless of wavelength.
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  So they all contribute.
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  Matt Edmundson: Which is fair enough.
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  Yeah, I get that.
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  So what about, um, night mode then on phones?
• 11:20
  Jen Oliver: Well, research is interesting.
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  There was a study in 2024 that suggested that overall screen
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  brightness might matter as much as, or more than the color of light.
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  So night mode combined with reduced brightness appears more
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  effective than either alone.
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  Matt Edmundson: That's interesting, isn't it?
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  So turning on the night mode, but keeping the brightness like at maximum.
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  Seems to be like self-defeating, isn't it?
• 11:45
  Mm. So, Chris, practical recommendations, you've bound to
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  have got some, but what are they?
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  Chris Smith: Yeah, A few things.
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  I think dimming your screens and, and using warmer color
• 11:54
  settings in the evening.
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  Worth a try.
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  Considering am tinted glasses, if you must use, uh, devices before bed,
• 12:01
  and ideally establishing a consistent time, say two hours before sleep when
• 12:06
  you set devices aside altogether.
• 12:09
  Jen Oliver: So one thing we should address.
• 12:11
  Um, is the persistent myth that blue light from screens damages your
• 12:16
  eyes And it's important to note that current evidence doesn't support this,
• 12:20
  Matt Edmundson: which is interesting, isn't it?
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  'cause I, there's a lot of marketing hype out there and I know we're,
• 12:24
  we're, you know, we are always down on marketing hype, but there is a lot of
• 12:27
  marketing hype out there about protecting your eyes from the harmful blue.
• 12:31
  Chris Smith: Yeah, you can get blue light treatment so it can get blue
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  light well, protection from blue light.
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  So it's a, it's a complete kind of hypocrisy.
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  And the confusion comes from laboratory studies using extremely high intensity
• 12:42
  blue light on isolated cells.
• 12:45
  But the thing is, screens emit far less blue light than natural sunlight does.
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  The sun delivers up to 1000 times more blue light.
• 12:53
  Than you'd get from your electronic device.
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  So if a screen blue light was genuinely harmful to our retinas, outdoor
• 13:00
  sunlight would be catastrophic.
• 13:02
  Yeah.
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  Our eyes, of course, can handle daylight fine.
• 13:05
  Jen Oliver: In the American Academy of Ophthalmology, they stated that there's
• 13:08
  insufficient evidence that blue light from devices damages eyes, what screens
• 13:13
  do, cause its digital eye strain, dry eyes, fatigue, headaches, but that's
• 13:19
  from prolonged screen use and reduce blinking, not the blue light itself.
• 13:24
  Matt Edmundson: That's interesting, Jen.
• 13:25
  So any more recommendations, Chris?
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  Chris Smith: Yeah, so there are some simple environmental
• 13:30
  changes that can help too.
• 13:31
  So, switching to warm colored, dim lighting in the evening or bulbs
• 13:35
  with, uh, lower color temperatures.
• 13:37
  That reduces blue light exposure without requiring glasses or screen changes.
• 13:41
  Jen Oliver: Yeah, and don't over overlook the power of getting
• 13:43
  bright light during the day.
• 13:45
  So getting outside for natural daylight, especially in the morning, that
• 13:48
  actually strengthens your circadian rhythms, and so it might reduce your
• 13:52
  sensitivity to evening light disruption.
• 13:54
  It's not just about avoiding blue light at night.
• 13:57
  It's about getting enough at the right times.
• 13:59
  Matt Edmundson: So morning sunlight then is my friend, if I understand it.
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  But late night phone scrolling is perhaps a frenemy.
• 14:08
  I just like that word frenemy.
• 14:09
  Had to get it in.
• 14:11
  Chris Smith: That's, it's a bit too Gen Z for me.
• 14:15
  Jen Oliver: We're done with the kids
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  Matt Edmundson: Z or Gen Z.
• 14:15
  Jen Oliver: It's okay.
• 14:16
  Matt Edmundson: I
• 14:16
  dunno,
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  Chris Smith: I dunno
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  which generation we're in these days.
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  Alpha, beta, I, I dunno.
• 14:20
  Um, but no, you, you're right.
• 14:22
  I mean the real concern here with blue, blue light is.
• 14:26
  The, uh, circadian disruption rather than eye damage itself.
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  And this connects to everything else we've discussed on this podcast.
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  So sleep quality affects cognitive function, mood, metabolism,
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  immune function, everything.
• 14:39
  Jen Oliver: And the circadian system also influences when we
• 14:42
  feel hungry, when we have energy, and when hormones are released.
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  So disrupting it with mistimed light exposure can have ripple
• 14:50
  effects throughout your biology.
• 14:53
  Chris Smith: The good news.
• 14:54
  If there is some good news is that blue light exposure during
• 14:57
  the day is actually beneficial.
• 14:58
  It promotes alertness and it helps reinforce strong circadian rhythms.
• 15:02
  As Jen was saying, it's specifically the evening exposure that causes these
• 15:06
  problems that we're talking about.
• 15:07
  Matt Edmundson: Yeah, and listening to you guys talk, I'm realizing maybe just
• 15:10
  five more minutes of scrolling might be costing me more than I thought.
• 15:15
  So not just lost sleep, but lower quality of sleep when I do finally drop off.
• 15:20
  Jen Oliver: So why does blue light affect sleep?
• 15:24
  Chris Smith: Blue light affects sleep because specialized cells in your
• 15:27
  retina containing melanopsin are highly sensitive to blue wavelengths.
• 15:32
  When these cells detect blue light, they signal to your brain's master clock
• 15:36
  that it's daytime, which suppresses melatonin production and delays your
• 15:39
  body's natural wind down process.
• 15:42
  Matt Edmundson: So every time I check my phone at 11:00 PM my brain genuinely
• 15:47
  thinks I've glimpsed the sunrise.
• 15:49
  And I wonder, I can't sleep after a scrolling session.
• 15:54
  Jen Oliver: Now you know why dimming your screens using warmer light settings
• 15:58
  and ideally putting devices away a couple of hours before bed can make
• 16:02
  such a difference to sleep quality.
• 16:05
  Your circadian system simply can't tell the difference between
• 16:09
  your phone and the morning sun.
• 16:11
  That's it for this week.
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  Make sure you hit that subscribe button.
• 16:15
  We're unpacking the science behind everyday questions each week.
• 16:19
  Tell us in the comments what you'd like us to explore.
• 16:22
  Thanks for geeking out with us, but for now, that's it from me.
• 16:26
  Matt Edmundson: That's it from me,
• 16:27
  Chris Smith: and that's it from me.
• 16:29
  Jen Oliver: Bye for now.