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Comment by hollerith | Hacker News Reader

>the 90 or so minutes up to sunrise

That greatly helps me get to sleep by 11p, too, but IIUC has nothing to do with this submission: we know why exposure to the light of the sun when the sun is very low in the sky affects the circadian rhythm (namely, via its effect on intrinsically-photosensitive retinal ganglion cells) and it has nothing to do with the red and infrared photons we are talking about here. (It has rather to do with a particular ratio of yellow photons to blue photons according to Andrew Huberman. Also, I suspect that there aren't sufficient fluxes of red and infrared photons outdoors before sunrise.)

The point is that you need to go outside again later in the day -- or get your infrared or red photons some other way -- to "nourish" your mitochondria in the way we are talking about here. They're separate health effects of light (or EM radiation to be precise) just like the production of vitamin D is again a separate health effect.

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Image with the light sensitivity of the photoreceptor:

https://en.wikipedia.org/wiki/Intrinsically_photosensitive_r...

Note: Melanopsin is the name of the ipRGC's photopigments.

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I've seems studies showing that genetically modified blind mices with ipRGC had circadian cycle. And that just a few photons of blue light is capable of suppress melatonin production in humans.

But I haven't seem anything about supression of melatonin being regulated by the ratio of yellow light and blue light. Could you provide a source?

Neuroscientist Andrew Huberman says it in episode 2 of the Huberman Lab Podcast. Sorry I don't recall where in the episode.

Huberman never specifies how low in the sky the sun needs to be for the sunlight (and my guess it is specifically the indirect fraction of the sunlight) to have a strong effect on the timing of the circadian clock.

"Indirect": scattered by the atmosphere.

I tried to corroborate with other sources, but gave up after about 60 min in a search engine. I have corroborated by my own experience though (I aim to go outside about 10 minutes before sunrise, but sometime I am delayed by up to 30 min) and the experience of a friend. Also of course the grandparent of your comment is corroboration of one half of the hypothesis (the other half being the assertion that when the sun is high in the sky, it has neglible effect on the timing of the biological clock).

He says that on a cloudless day, you only need 5 minutes of exposure provided your eyes have a clear view of the sky (i.e., no brim of a hat obscuring half of the sky). On a very overcast day, 20 min might be required.

There are plenty of evidence that the activation of ipRGC inhibits melatonin production.

My question was about the "ratio of yellow photons to blue photons".

Fun fact: Blue light can stimulates melanogenesis in dark-skinned individual (type III and above) [1], no UV required. This process is mediated by an Opsin, like our vision.

This is a somewhat recent discovery (~2010) and the physiological effects are still largely unknown. Most studies on the subject are concerned about hyperpigmentation and oxidative stress.

[1] https://www.sciencedirect.com/science/article/pii/S0022202X1...

The "ratio of yellow photons to blue photons" is a verbatim quote from the podcast episode. Huberman didn't expand on that in the episode, and (again) my search for specifics yielded no additional understanding.

But Huberman was quite clear that the spectrum of light when the sun is low in the sky is different somehow from the spectrum when it is high, and the eye has some way to detect this difference.

The important fact is that when the sun is high in the sky, the light has very little effect on the timing of a person's circadian rhythm, and Huberman was quite clear on that too.

Most people do not seem to know that yet!

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