5 ms·

> Type "blue light circadian rhythm study" on google and you basically only find studies supporting that blue light has a negative impact. But the moment you a

> Type "blue light circadian rhythm study" on google and you basically only find studies supporting that blue light has a negative impact. But the moment you actually evaluate the studies, you'll find that almost all * don't research blue light specifically, but light at all * use unrealistic settings, like 4 to 8 hours bedtime reading (really) * don't properly control for other known sleep affecting factors - and have small sample groups so they can't rely on the law of large numbers to solve that issue * only measure melatonin, not actual sleep. If you filter those out, the result ist basically zero quality studies. I'm aware that many people swear that this works, but there really is not much scientific support for the theory. Just for comparison: Full sunlight has up to 30000lux of blue light alone, while a very bright phone screen, set to all white, manages to output at most 300lux of blue light. There may be a real effect here, but it has to be weak, else people in scandinavia would have severe problems with their circadian rhythms.

herf 7y ago
It is important first to say that sleep optimization is not the only goal with these things, and understanding the timing of melatonin (not just melatonin suppression) is how we find out "when" the circadian clock is set. The circadian system is loosely coupled to sleep, but it affects many other parts of the body. So if your rhythms are more than 2-3 hours out of sync you will definitely have more trouble sleeping, but this is not the only effect, which is why we work with people studying other topics also. But overall, yes, I think we'll learn that regular room lighting has at least as big an effect as screens, and that's because in terms of "hours" people spend a lot of them in general illumination, but often only check their phone a few times, or watch a dark movie, which isn't very bright. It's only some of us that code all night in front of a bright screen.
lm28469 7y ago
> Full sunlight has up to 30000lux of blue light alone Well yeah that's the whole point, blue light during the day is perfectly fine, that's how your body knows it's time to get shit done, sitting in front a screen after sunset during X hours _will_ fuck up your rhythm and blocking blue light will moderately mitigate the issue. > else people in scandinavia would have severe problems with their circadian rhythms. They do, just like you do when we switch to winter time. It's not a "problem" though, it's just our body's natural response. The problem arise when you shift your rhythm so bad that it impact your life / work schedules. > If you filter those out, the result ist basically zero quality studies. It's 100% a fact that blue light is the light which impact the production of melatonin the most, and that melatonin directly regulate your circadian rhythm.
- bildung 7y ago
  Even on a cloudy winter day the sun's luminocity is about 20 times higher than a very bright phone display. My point is that it is not reasonable to assume a strong physical reaction if the artifical light is so much weaker. Note I'm not denying that there isn't a small effect! But it is probably dwarved in comparison to a change in eating habits, anti stress methods like meditation, sports and so on. > It's 100% a fact that blue light is the light which impact the production of melatonin the most, and that melatonin directly regulate your circadian rhythm. Then why don't most studies study effects on the actual circadian rhythm? My guess is because the results there are less clear with actual sleep (i.e. they actually studied both but only published the "good" results - a sad side effect of publication bias). BTW the same is true for light therapy for prevention of winter depression: There probably is an effect, but it is so weak that rigorous meta analysises don't show real evidence. My overall point is: There seldom are strong effects with most treatments of this kind. If there were, we already would have found out in pre science times. People are doing artifical lighting for thousands of years (think campfires, not LED lights).
  - jiofih 7y ago
    Campfires are not artificial light. This is about blue light after all. You need to show some data to back your statements besides hand-waving all existing studies in one swoop.
    - bildung 7y ago
      Campfires are artifical as in they are not the sun, and people were exposed to their radiation for millenia. A fire obviously emits most of its electromagnetic radiation in the IR band, but it the emission goes down right into UV. This is not exactly rocket science, just point a UV/Vis spectrometer at a fire and see for yourself. I'm not quite sure why you think I should provide data - I'm not the person postulating the effect of blue light. But anyway. You can find examples of the sun's illuminance all over the net, for example Wikipedia has a list here: https://en.wikipedia.org/wiki/Illuminance https://en.wikipedia.org/wiki/Illuminance Illuminance usually only covers the VIS part of the EM spectrum, so all of about 380-700nm. So 1/4 to 1/3 of that is the cold light part. The radiation emmited from a heat source can be determined using Planck's law. A campfire is about 1400K. Here you can see that the higher the temperature, the more the maximum radion shifts into smaller wavelengths: https://www.spektrum.de/lexika/images/geo/f4f1653_w.jpg https://www.spektrum.de/lexika/images/geo/f4f1653_w.jpg So obviously the sun with about 6000k has way more UV and blue light parts, but a campfire is still hot enough that the absolute amount of blue light emitted trumps every phone screen. Yes, probably more than 95% will be IR, but than again the overall luminocity of a campfire is about 10kW. For light therapy and winter depression I refer you to the excellent chochrane review: https://www.cochrane.org/CD011269/DEPRESSN_light-therapy-prevention-winter-depression https://www.cochrane.org/CD011269/DEPRESSN_light-therapy-pre... As to my criticisms regarding most studies about the effects of light: You can look them up yourself, most of them apply to the studies linked at f.lux's research links: https://justgetflux.com/research.html https://justgetflux.com/research.html For example the top two studies there: "Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans" used 8h room light and didn't check for blue light at all. Neither did they look at actual sleep patterns. "The human circadian system adapts to prior photic history" : 6.5h of exposure, no blue light specifically, only melatonin, no actual sleep measurments. Again: I'm not the person making claims here. I would be delighted to see some proper studies showing the effects of blue light.

herf 7y ago

It is important first to say that sleep optimization is not the only goal with these things, and understanding the timing of melatonin (not just melatonin suppression) is how we find out "when" the circadian clock is set. The circadian system is loosely coupled to sleep, but it affects many other parts of the body. So if your rhythms are more than 2-3 hours out of sync you will definitely have more trouble sleeping, but this is not the only effect, which is why we work with people studying other topics also. But overall, yes, I think we'll learn that regular room lighting has at least as big an effect as screens, and that's because in terms of "hours" people spend a lot of them in general illumination, but often only check their phone a few times, or watch a dark movie, which isn't very bright. It's only some of us that code all night in front of a bright screen.

lm28469 7y ago

> Full sunlight has up to 30000lux of blue light alone Well yeah that's the whole point, blue light during the day is perfectly fine, that's how your body knows it's time to get shit done, sitting in front a screen after sunset during X hours _will_ fuck up your rhythm and blocking blue light will moderately mitigate the issue. > else people in scandinavia would have severe problems with their circadian rhythms. They do, just like you do when we switch to winter time. It's not a "problem" though, it's just our body's natural response. The problem arise when you shift your rhythm so bad that it impact your life / work schedules. > If you filter those out, the result ist basically zero quality studies. It's 100% a fact that blue light is the light which impact the production of melatonin the most, and that melatonin directly regulate your circadian rhythm.

bildung 7y ago
Even on a cloudy winter day the sun's luminocity is about 20 times higher than a very bright phone display. My point is that it is not reasonable to assume a strong physical reaction if the artifical light is so much weaker. Note I'm not denying that there isn't a small effect! But it is probably dwarved in comparison to a change in eating habits, anti stress methods like meditation, sports and so on. > It's 100% a fact that blue light is the light which impact the production of melatonin the most, and that melatonin directly regulate your circadian rhythm. Then why don't most studies study effects on the actual circadian rhythm? My guess is because the results there are less clear with actual sleep (i.e. they actually studied both but only published the "good" results - a sad side effect of publication bias). BTW the same is true for light therapy for prevention of winter depression: There probably is an effect, but it is so weak that rigorous meta analysises don't show real evidence. My overall point is: There seldom are strong effects with most treatments of this kind. If there were, we already would have found out in pre science times. People are doing artifical lighting for thousands of years (think campfires, not LED lights).
- jiofih 7y ago
  Campfires are not artificial light. This is about blue light after all. You need to show some data to back your statements besides hand-waving all existing studies in one swoop.
  - bildung 7y ago
    Campfires are artifical as in they are not the sun, and people were exposed to their radiation for millenia. A fire obviously emits most of its electromagnetic radiation in the IR band, but it the emission goes down right into UV. This is not exactly rocket science, just point a UV/Vis spectrometer at a fire and see for yourself. I'm not quite sure why you think I should provide data - I'm not the person postulating the effect of blue light. But anyway. You can find examples of the sun's illuminance all over the net, for example Wikipedia has a list here: https://en.wikipedia.org/wiki/Illuminance https://en.wikipedia.org/wiki/Illuminance Illuminance usually only covers the VIS part of the EM spectrum, so all of about 380-700nm. So 1/4 to 1/3 of that is the cold light part. The radiation emmited from a heat source can be determined using Planck's law. A campfire is about 1400K. Here you can see that the higher the temperature, the more the maximum radion shifts into smaller wavelengths: https://www.spektrum.de/lexika/images/geo/f4f1653_w.jpg https://www.spektrum.de/lexika/images/geo/f4f1653_w.jpg So obviously the sun with about 6000k has way more UV and blue light parts, but a campfire is still hot enough that the absolute amount of blue light emitted trumps every phone screen. Yes, probably more than 95% will be IR, but than again the overall luminocity of a campfire is about 10kW. For light therapy and winter depression I refer you to the excellent chochrane review: https://www.cochrane.org/CD011269/DEPRESSN_light-therapy-prevention-winter-depression https://www.cochrane.org/CD011269/DEPRESSN_light-therapy-pre... As to my criticisms regarding most studies about the effects of light: You can look them up yourself, most of them apply to the studies linked at f.lux's research links: https://justgetflux.com/research.html https://justgetflux.com/research.html For example the top two studies there: "Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans" used 8h room light and didn't check for blue light at all. Neither did they look at actual sleep patterns. "The human circadian system adapts to prior photic history" : 6.5h of exposure, no blue light specifically, only melatonin, no actual sleep measurments. Again: I'm not the person making claims here. I would be delighted to see some proper studies showing the effects of blue light.