My understanding is that there are still significant unknowns on the exact mechanisms of entrainment, and I don’t dispute that yellow-blue (YB) contrasts play a role. I considered mentioning it in this post, but my understanding is that it is more of a secondary point compared to the significance of the timing of bright, blue light exposure. Curious to see any evidence for your/Huberman’s assertion that early morning light exposure in the absence of YB contrasts has little effect on entrainment. This seems to contradict most of the literature I’ve seen.
The balance of my post more closely reflects this 2021 summary of the state of the art by Russell Foster (who was crucial in the discovery of the role ipRGCs). I’m inclined to trust his overview of the literature over Huberman, who has spread himself quite thin in the past. Having said that am wary that this summary is from 2021 and am less familiar with research from the last couple of years….
If there is anything specific you think is factually inaccurate in the essay, I would be more than happy to discuss.
I know you just said that you don’t completely trust Huberman, but just today, Huberman published a 30-minute video titled “Master your sleep and be more alert when awake”. I listened to it (twice) to refresh my memory and to see if his advice changed.
He mentions yellow-blue (YB) contrasts once (at https://www.youtube.com/watch?v=lIo9FcrljDk&t=502s) and at least thrice he mentions the desirability of exposure to outdoor light when the sun is at a low angle (close to the horizon). As anyone can see by looking around at dawn and again at mid-day, at dawn some parts of the sky will be yellowish (particularly, the parts of the sky near the sun) or even orange whereas other parts will range from pale blue to something like turquoise to deep blue whereas at mid-day the sun is white, the part of the sky near the sun is blue and the blue parts of the sky are essentially all the same shade or hue of blue.
He also says that outdoor light (directly from the sun or indirectly via atmospheric scattering) is the best kind of light for maintaining a healthy circadian rhythm, but that if getting outdoors early enough that the sun is still low in the sky is impractical, artificial light can be effective, particularly blue-heavy artificial light.
I’ve been help greatly over the last 2 years by a protocol in which I get outdoor light almost every morning when the YB contrasts are at its most extreme, namely between about 20 min before sunrise and about 10 min after sunrise on clear days and a little later on cloudy days. (The other element of my protocol that I know to be essential is strictly limit my exposure to light between 23:00 and 05:00.) I was motivated to comment on your post because it did not contain enough information to help someone sufficiently similar to me (the me of 2 years ago) to achieve the very welcome results I achieved: I’m pretty sure that even very bright artificial light from ordinary LED lights that most of us have in our home (even very many of them shining all at once) would not have helped me nearly as much.
Huberman is not so insistent on getting outside during this 30-minute interval of maximum YB contrast as my protocol is. In fact in today’s video he says that he himself often gets outside only after the sun has been out for an hour or 2 and is consequently no longer particularly near the horizon.
Health-conscious people apply a (software-based) filter to their screens in the evening to reduce blue light emitted from the screen. On iOS this is called Night Shift. If your rendition of the effects of light on the circadian rhythm (CR) is complete, then they’re doing everything they can do, but if YB contrasts have important effects on the CR, it might be useful in addition to eliminate YB contrasts on our digital devices (which Night Shift and its analogs on the other platforms do not eliminate). This can be done by turning everything shades of gray. (On iOS for example, this can be achieved in Settings > Accessibility > Display & Text Size > Color Filters > Grayscale and can be combined with or “overlaid on” Night Shift.) I and others do this (turn of a filter that makes everything “grayscale”) routinely to make it more likely that we will get sleepy sufficiently early in the evening. Additional people report that they like to keep their screens grayscale, but do not cite the CR as the reason for their doing so.
Is a computer screen bright enough such that YB contrasts on the screen can activate the machinery in the retina that is activated by a sunrise? I’m not sure, but I choose to eliminate YB contrasts on my screens just in case it is.
Finally let me quote what I consider the main takeaway from the video Huberman posted today, which I expect we both agree with:
Get up each morning, try to get outside. I know that can be challenging for people, but anywhere from 2 to 10 min of sun exposure will work well for most people. If you can’t do it every day or if you sleep through this period of early-day low-solar angle, don’t worry about it. The systems in the body—these hormone systems and neurotransmitter systems—that make you awake at certain periods of the day and sleepy at other times are operating by averaging when you view the brightest light.
Thanks for the detailed reply.
My understanding is that there are still significant unknowns on the exact mechanisms of entrainment, and I don’t dispute that yellow-blue (YB) contrasts play a role. I considered mentioning it in this post, but my understanding is that it is more of a secondary point compared to the significance of the timing of bright, blue light exposure. Curious to see any evidence for your/Huberman’s assertion that early morning light exposure in the absence of YB contrasts has little effect on entrainment. This seems to contradict most of the literature I’ve seen.
The balance of my post more closely reflects this 2021 summary of the state of the art by Russell Foster (who was crucial in the discovery of the role ipRGCs). I’m inclined to trust his overview of the literature over Huberman, who has spread himself quite thin in the past. Having said that am wary that this summary is from 2021 and am less familiar with research from the last couple of years….
If there is anything specific you think is factually inaccurate in the essay, I would be more than happy to discuss.
I know you just said that you don’t completely trust Huberman, but just today, Huberman published a 30-minute video titled “Master your sleep and be more alert when awake”. I listened to it (twice) to refresh my memory and to see if his advice changed.
He mentions yellow-blue (YB) contrasts once (at https://www.youtube.com/watch?v=lIo9FcrljDk&t=502s) and at least thrice he mentions the desirability of exposure to outdoor light when the sun is at a low angle (close to the horizon). As anyone can see by looking around at dawn and again at mid-day, at dawn some parts of the sky will be yellowish (particularly, the parts of the sky near the sun) or even orange whereas other parts will range from pale blue to something like turquoise to deep blue whereas at mid-day the sun is white, the part of the sky near the sun is blue and the blue parts of the sky are essentially all the same shade or hue of blue.
He also says that outdoor light (directly from the sun or indirectly via atmospheric scattering) is the best kind of light for maintaining a healthy circadian rhythm, but that if getting outdoors early enough that the sun is still low in the sky is impractical, artificial light can be effective, particularly blue-heavy artificial light.
I’ve been help greatly over the last 2 years by a protocol in which I get outdoor light almost every morning when the YB contrasts are at its most extreme, namely between about 20 min before sunrise and about 10 min after sunrise on clear days and a little later on cloudy days. (The other element of my protocol that I know to be essential is strictly limit my exposure to light between 23:00 and 05:00.) I was motivated to comment on your post because it did not contain enough information to help someone sufficiently similar to me (the me of 2 years ago) to achieve the very welcome results I achieved: I’m pretty sure that even very bright artificial light from ordinary LED lights that most of us have in our home (even very many of them shining all at once) would not have helped me nearly as much.
Huberman is not so insistent on getting outside during this 30-minute interval of maximum YB contrast as my protocol is. In fact in today’s video he says that he himself often gets outside only after the sun has been out for an hour or 2 and is consequently no longer particularly near the horizon.
Health-conscious people apply a (software-based) filter to their screens in the evening to reduce blue light emitted from the screen. On iOS this is called Night Shift. If your rendition of the effects of light on the circadian rhythm (CR) is complete, then they’re doing everything they can do, but if YB contrasts have important effects on the CR, it might be useful in addition to eliminate YB contrasts on our digital devices (which Night Shift and its analogs on the other platforms do not eliminate). This can be done by turning everything shades of gray. (On iOS for example, this can be achieved in Settings > Accessibility > Display & Text Size > Color Filters > Grayscale and can be combined with or “overlaid on” Night Shift.) I and others do this (turn of a filter that makes everything “grayscale”) routinely to make it more likely that we will get sleepy sufficiently early in the evening. Additional people report that they like to keep their screens grayscale, but do not cite the CR as the reason for their doing so.
Is a computer screen bright enough such that YB contrasts on the screen can activate the machinery in the retina that is activated by a sunrise? I’m not sure, but I choose to eliminate YB contrasts on my screens just in case it is.
Finally let me quote what I consider the main takeaway from the video Huberman posted today, which I expect we both agree with:
https://www.youtube.com/watch?v=lIo9FcrljDk&t=816s