Are we sure
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A very niteresting article about blue light :
https://www.techradar.com/news/smartphone-night-modes-may-not-actually-help-you-sleep-say-scientists -
This study answers an important question in mice, and we don't think it applies (yet) to humans.
What's amazing is that there is a study saying that there is no such effect in humans in the very same issue. So read this one too: https://www.cell.com/current-biology/fulltext/S0960-9822(19)31501-5
Regarding the Mouland study, here are some details:
- This study does not dispute the contribution of melanopsin, which is the blue-cyan pigment that started this whole "blue light" thing. The question is what's going on in addition to melanopsin.
- This is a demonstration in mice, which have a UV-sensitive S-cone, not in humans. The mice are nocturnal, not active during the day like humans, so you might say they need different cues about dawn and dusk.
- Several studies in humans (see below) say that humans tend to be more sensitive to blue even than melanopsin would predict (all of these things are measured at night) - others (including the above by Spitschan) say there is no effect
- In the above experiment, the blue stimulus is much dimmer than the orange one, so we don't know if this effect would work at light levels that humans would see as comfortable after dark, and this is the main problem for our own lighting
Stepping back, first: the reason people talk about "blue light" is because of the discovery of melanopsin in the eye (which is sensitive to cyan).
The question this paper addresses isn't about melanopsin - instead, it asks if there is an additional response at dusk (when blue > cyan) that says "it's more stimulating" or "it's less stimulating". In other words, does melanopsin explain everything, or are the cones boosting it? (Probably the latter is true.)
So far in humans, there are mixed reports about whether or not there is such an effect:
- The Thapan study from 2001 indicates extra blue-light sensitivity in addition to melanopsin. Lights are seen for a half hour at night. https://doi.org/10.1111/j.1469-7793.2001.t01-1-00261.x
- The Spitschan study from this same issue of Current Biology says there is no effect in either direction when comparing S-cone contrast. The lights here are "pink" (which has a lot of blue) and "orange".
- The Brainard 2015 study compares 4000k to 17000k lights: at the same "melanopic" level the 17000k lights do a lot more melatonin suppression: https://jdc.jefferson.edu/cgi/viewcontent.cgi?article=1081&context=neurologyfp
- There is one important study in humans (Gooley 2010) that says we can be more sensitive to 555nm light after two days in dim light, so that mirrors this study. But this is not exactly comparable to the study cited here due to sensitization: it stands on its own due to the duration of the experiment.
That said, it's very compelling to think of twilight (the "blue hour") which has a kind of purple hue, as having a beneficial effect on circadian entrainment - why would we ignore it in our lighting schemes? There is a difference between 6 hours of "warm light" at night and 1 hour of twilight as is seen in nature, so it's unclear how to merge the two. Our history with electric lighting doesn't simulate twilight, and it's not clear exactly what it would look like.
Overall, the other research so far in humans says there is either no effect, or that it goes the other direction. These effects are sort of "boosts" to the overall system that detects day and night, and there is likely something like this going on with humans too. It is important to do more research to find out what's going on exactly.
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It would be interesting to include the blue hour (dark cold blue light after the golden hour) in the cycle as an option and see what it does.
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@herf Thanks for that great reply! I gave a much shorter, more general response - basically - 1. one study does not "debunk", 2. mice are not human and 3. It's all a lot more complicated!!
I didn't want to spend much time, because it doesn't appear that this blog is very active.. most posts are years old. That is sad, b/c this is such an important topic, which I am fairly new to, and am trying to soak up as much info as I can.
I don't know if you'll even see this.
I come from a 'science' background, so I know how to read papers, and I know about the 'politics' involved in all areas of science, and publishing, AND the media (which uses 'sciencey sounding blogs, etc to often present completely misrepresented info).
I do think it's important to not send the message "blue light bad" - as you astutely pointed out in a reply in another thread - it does a lot of good things.. in fact full spectrum/blue lights have been used to (successfully treat depression), particularly SAD (seasonal affective disorder). I do suffer from mild low mood during the cold dark days where I live, and one of those lights helped me tremendously. In fact, I'm looking to get another one! Some would say, look at the computer - but the light from the computer is different - and if one is 'wired' , the Wifi exposure is probably more deleterious.
As you pointed out, it is the HUGELY increased exposure to blue light at night (and I believe not just the visible light, but the other radiation - the 'dirty electricity from the LED bulbs, etc.; and of course the EMF. I was wondering if you had any comments about those things, as you seem very knowledgeable.
I need to read through your references.. but I think there is something just to light in general. A person can do a lot for their sleep just by darkening rooms, shutting off lights in the evening - following nature.
Bottom line - as you point out. this is a complicated issue, we are only scratching the surface - and it is going to be further complicated by the opposition by big tech - who seem to not just rule science, but the world now. :)
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Just this week, there is a new publication that says in humans that the s-cone is able to suppress more melatonin than a similar source with less "blue":
https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpi.12719
But this isn't the whole point: my point in writing that post was to say that "blue" in this context is not what everyone thinks. The first thing is that MOST of the signal from the eye to the brain is from the melanopsin photopigment (which sees blue/cyan). The mouse paper (Mouland) then uses "blue/yellow" to refer to the cone color "blue" sensation in addition to melanopsin. They are basically saying, if we use the same amount of cyan and add blue or yellow, then what happens?
Thus most people can think (and I would encourage them to think), it's probably still 80% melanopsin doing the work in a lot of conditions, and for shorter durations, the only information we have in humans is: more blue is more stimulating, or it has a small effect.
As for EMF I think non-ionizing radiation interactions with leukemia+cancer (from powerlines, wi-fi, cell phones etc) is probably unproven, mainly because most of the studies are association studies. This means to me that light/sound/etc. could be correlated with those exposures, and the early work on childhood leukemia did not take a nuanced view of light exposure and other factors into account. So if you have a powerline near your bedroom window, you likely have a street lamp also. We should skeptically ask if the light exposure or the EMF is having a bigger effect:
https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/electromagnetic-fields-fact-sheetHowever, here is a recent study about holding a cellphone next to your head, which I wonder about: https://www.statnews.com/2016/05/27/cellphone-study-explainer/
