Effects of calibrated blue–yellow changes in light on the human circadian clock, 2024, Blume et al

Discussion in 'Other health news and research' started by Hutan, Jun 9, 2024 at 11:53 AM.

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  1. Hutan

    Hutan Moderator Staff Member

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    https://www.nature.com/articles/s41562-023-01791-7

    Abstract
    Evening exposure to short-wavelength light can affect the circadian clock, sleep and alertness. Intrinsically photosensitive retinal ganglion cells expressing melanopsin are thought to be the primary drivers of these effects. Whether colour-sensitive cones also contribute is unclear.

    Here, using calibrated silent-substitution changes in light colour along the blue–yellow axis, we investigated whether mechanisms of colour vision affect the human circadian system and sleep. In a 32.5-h repeated within-subjects protocol, 16 healthy participants were exposed to three different light scenarios for 1 h starting 30 min after habitual bedtime: baseline control condition (93.5 photopic lux), intermittently flickering (1 Hz, 30 s on–off) yellow-bright light (123.5 photopic lux) and intermittently flickering blue-dim light (67.0 photopic lux), all calibrated to have equal melanopsin excitation.

    We did not find conclusive evidence for differences between the three lighting conditions regarding circadian melatonin phase delays, melatonin suppression, subjective sleepiness, psychomotor vigilance or sleep.
     
  2. Hutan

    Hutan Moderator Staff Member

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    Article about the findings

    Blue Light May Not Be Keeping You Awake After All
    A new study shows that the brightness of light matters more than its color.

    KEY POINTS
    • Researchers exposed healthy subjects to blue, yellow, and white light for an hour before bed.
    • The color of light made no difference to participants' level of drowsiness or sleep quality.
    • Light-sensitive ganglion cells in the eye, not color-producing cone cells, affect circadian rhythm.
    “We found no evidence that the variation of light color along a blue-yellow dimension plays a relevant role for the human internal clock or sleep,” says Christine Blume, lead study author and post-doctoral researcher at the University of Basel’s Centre for Chronobiology. “Rather, our results support the findings of many other studies that the light-sensitive ganglion cells are most important for the human internal clock.”

    ...

    So does that mean the Night Shift function on your phone is useless?

    Though another study has shown that warm-light screen settings don’t actually improve sleep quality, Blume says we shouldn’t do away with them just yet. Most night options on electronic devices change not only the color temperature of the light they emit but also its intensity, which does have an impact on sleep.​
     
  3. JemPD

    JemPD Senior Member (Voting Rights)

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    interesting. I struggle with the night light settings on my screens because the yellow makes me able to see/focus less well, so i have to turn up the brightness. If i have full daylight setting ie blue, i can see at much lower levels of brightness, which has always felt instinctively better.
     
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  4. bobbler

    bobbler Senior Member (Voting Rights)

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    Interesting

    it also makes me think given how many assumed paradigms and truisms that medicine happily based things on like a foundation have turned out to have no science (just be values based on upbringing and mother knows best this is his one behaves) or the old ‘famous claimed experiment’ of the past.

    is it not time someone investigated this light and circadian rhythm one better than it has been. I know lots of old psych experiments have been debunked.

    I know there was a tv one about 8yrs ago. But it was one experiment. Lots if the ‘it must be trye’ is based on citing blind people and then people who were put in a cellar

    surely you want to compare just removing all the clocks and things that indicate time of year and ergo time and have enough people just living life with light to see if it’s actually the whole light thing that’s a differentiator.

    and the having people live in a cave with no clocks for thirty days or whatever could have had two controls: one who got light and one who gif radio at the start of the day.

    the surety with which it has ducaltated so much if what has been advised to people and done based on its assumptions in medicine vs the robustness of the research and enquiry in this area to me has ever quite matched

    but then it often doesn’t when it’s something everyone is happy to think makes sense (feasible) most want to believe and you do it just to have about enough one-liners to sound convincing - like citing blind people.

    it’s a real shame because I bet there is not just a lot more going on but if they got some properly forensic measures across a range of circumstances (even if they were less dramatic and therefore convincing) they might not just have more useful data to help with diseases (and now we know there are clock genes and proteins might be insightful for example) as well as then offering easier options for methodology if they hone what’s going on. So you no longer have to do the basement gif a month and know what caries with what etc
     
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  5. alex3619

    alex3619 Senior Member (Voting Rights)

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    This might mean we need more information to interpret this. By calibrating to equal melanopsin excitation they introduce a specific bias. The yellow light is much more intense than the blue for equal response. So care needs to be taken in interpreting this study. In doing this they showed the colour makes no difference at equal excitation levels. However its not equal excitation under most circumstances, which implies colour is important.

    Its a little like broad chemical intolerance. A lot of an intense substance is bad, but a small amount is no different from a less intense substance. Quantity matters. So a huge serving of delicious apples to someone who is salicylate intolerant is similar to a small serving of some spicy food.

    However its clear we need more research into circadian regulation and disruption. That includes diet, not just what is eaten but when. Then of course we need to figure out how this fits with all the ME research. It is not going to be simple.
     
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  6. bobbler

    bobbler Senior Member (Voting Rights)

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    i haven’t read in depth but noting you bring in ME/CFS to this just flags the other issue: ‘calibrated to melanopsin excitation’ is likely to have both individual differences and within person differences (bad day good day etc)

    was it calibrated but to the eponymous ‘normal person’ (it’s possible even eye colour affects things with eg normal sun) or calibrated each time it was set up to that subjects level?

    because of course when you think of eg ME it would be interesting if they are starting to map the distribution on these things.

    I can sort of see that they tried to control other factors to just see whether colour itself is different- but this is where the issue with how the impact section got bunged on as an additional with the RAE to REF changes comes in.

    If that last section is just about selling application to real world in more PR language and plain spoken ie doesn’t include ‘method bits’ and yet most blue light devices vs yellow light need to be at a certain level for their use then that’s different to the ‘in theory’ of ‘if it was just colour’ making a difference tests to find out how the brain etc works /mechanisms. Even for medical ‘science’ part (ie the latter) there comes a point where the ‘in-between’ of these two levels needs to be brought in otherwise indeed the contrast and other factors start not being equal.

    tough area. I hope this is a map getting to the bottom of and not a do a quick experiment then give out advice it’s not fully confirmed thing , but the nature of things today …
     
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  7. Creekside

    Creekside Senior Member (Voting Rights)

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    There are a lot of factors where we have to do our own experiments to see how much effect they have on us. Maybe some people do notice a difference if they use the night setting on a screen, while others don't. If a factor is expensive, then testing whether it makes a significant--worth the expense--difference for you is worthwhile.
     
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  8. JemPD

    JemPD Senior Member (Voting Rights)

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    Struggling to follow what you mean/extrapolate to real life circumstances for my own use, feeling very foggy

    so do you mean that a long exposure to low brightness blue light will be worse than a long exposure to higher brightness yellow light?

    so i can keep it blue if i'm just using for a short time but change it to yellow with it a little brighter if i'm going to be using for a lonegr period?

    or???
     
  9. alex3619

    alex3619 Senior Member (Voting Rights)

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    No. I don't think so if I am interpreting you right. Blue light is more intense, so you can tolerate brighter yellow light for the same effect, again if I am interpreting this right. At the specific brightnesses (lux) used in the study, dim blue light and bright yellow light have the same outcome.

    We need to do our own testing, as usual. It also depends on what you are trying to do. I might want more blue light, or less, or even regular light, depending on my intent. I have still to figure out the general rules in any practical sense, as this requires experimenting on my circadian patterns, and they are still in flux. I have been dealing with circadian disorders for decades, and tonight for example I am not sleeping, which is leaving me wrecked, because I need to adjust my wake hours for my surgery in a few days. I can be wrecked before or after, but I do not want to be wrecked heading into hospital.
     
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