(silence) - Assuming that most people wake up in the morning, as opposed to night shift workers, et cetera, we could talk about later. But they wake up in the morning, so let's divide the day into quarters. What is the proper way to interact with light in the first part of the day?

- So I honestly think the easiest thing is waking up. Get as much light as you can. - Into your eyes. - Yeah, it's really nice. Your system is primed. If you're entrained, it's primed to get light. The sun should be out. Most animals in the wild, they actually seem to track the sun.

The sun has a huge influence on life on Earth. It's actually, life on Earth is because of sun. So that's easy. In the morning, when you wake up, you need light. - Okay, so what is the behavioral practice that you recommend? Does it, let's say somebody is in a condition where there's a lot of cloud cover.

- Yeah. - Is it important to get outside? - So I have to tell you, the cloudiest day is gonna be much more brighter than your room. You could ask any photographer. A cloudy day, unless it's really dark, dark clouds, usually cloudy days have much more bright outside than inside the room, even when you have good lighting inside the room.

So I think in the outside is usually, even when it's cloudy, you're gonna get enough intensity to help you adjust your cycle to the day-night cycle. - So how long do you, these are general rules of thumb, but how long do you recommend people go outside? - So if you do it daily, you possibly need very, if you do it daily, because remember, this thing is gonna happen on a daily matter.

So let's say 15 minutes. - So the clock is tracking it on a regular basis. - Absolutely, it's photon counting, it's tracking. I would say 15 minutes. If you don't do it daily, you may wanna increase it. And we'll talk about when you travel, what you could do. But yeah, 15 minutes should be fine.

You do it more, it doesn't hurt. - And through a window, I was, my understanding is that through a window, it dramatically decreases the amount of light energy. - It depends of how, you know, how thick the windows are and how dark they are. So it's, but it's also nice to go outside and to feel the season.

- Sunglasses off. - I don't use sunglasses. - But you have the Jordanian for pigment, you know, so. Yeah, whereas my eyes are very sensitive, right? - No, but I personally, you know, if I'm in the shade or if it's not incredibly bright, I try to, especially in the morning, but I'm also an early person.

So we have to differentiate between early. - What time do you wake up? - I wake up at 4.30 in the morning. - But the sun isn't out yet. - It's not out yet, so it's. - So what do you do? You turn on artificial lights? - I usually don't turn on artificial light because I know the sun is gonna come up eventually.

But that's why I don't like the change in the timing that they do. - Wait, but what do you do between 4.30 a.m. and 7 a.m.? - I mean, I just got my computer and my phone. So possibly I get enough light. But in reality, I mean, as long as you let your body get the morning sunlight, which I think is really, to me, and there's no evidence, but to me, this is, if you look at all animals, plants, this morning sunlight seems to be very important.

And I, you know, we don't have experiments to show it, but I have a gut feeling that it has a huge impact on humans. - Well, Jamie Zeitzer's lab at the Stanford Sleep Lab has shown that these early morning light flashes can adjust the total amount of sleep that one will get and makes it easier to get into sleep.

- Absolutely, absolutely. - Okay, so-- - And Ken Wright also did this beautiful camping experiments that showed-- - Right, maybe you should describe those, 'cause those are beautiful experiments. - They are beautiful experiments. He took these, you know, college students that had a late onset of sleep and late waking time.

And then he said, "Let's go camping "and just don't use any artificial light. "And you could go to sleep as late or as early as you want "and wake up as late as early." And he found a huge shift in their sleep pattern just by exposing them to the light-dark cycle.

I mean, so-- - And it lasted. - And it lasted. - Even after they came back. - Exactly. - I think it was two days of camping, reset the circadian clock. - Seven days, but it lasted. Yeah, it's pretty amazing. Yeah, it's really incredible. - Okay, so get bright light of some sort early in the day, ideally sunlight, even on a cloudy day, it's going to be brighter than indoor light.

- So that's easy. - Okay, so then-- - And the other thing that I would like to mention to people, if you think it's very dim outside, let's say it's very cloudy, stay longer. So remember, intensity is only one component. Duration is also important, because remember that the circadian system, it's not like the image system.

In the image system, you have to change every second because you're looking at different objects. You have to change your perception. But for the circadian system, it's trying to figure out where am I in the day-night cycle? So the more you give them the information, the better you are.

So if it's very bright, you don't need a lot, because it's clearly going to make you fire like crazy. But if it's not bright, stay longer. Stay for one hour, have your coffee outside or something like that. It's just going to help. - I think you said something extremely important, which is that this circadian system is trying to figure out when you are in time.

- Exactly. - Not where you are in space. - Sorry, I said where you are in time. I meant when you are. - Oh, no, no, I wasn't correcting you. I just meant that, I think fundamentally, that's the incredible thing about this system, that you have this clock, this 24-hour clock in your brain, but it needs to be synchronized to the outside.

So could we go a little deeper into this circadian setting behavior and come up with some general rules of thumb? So let's say it's a very bright day, extremely bright. No clouds, sun's out. You said 10 minutes, 15 minutes. And I'll tell you, if you're sensitive, you don't even have to go in the sun.

You could be in the shade. There's going to be so many photons out there in the shade. It's going to be perfect. You don't even have to see the sun. You don't have to have the sun. It's great for vitamin D. That's a different story. You could do this for your skin and protect your skin.

That's not my area of expertise. But for that effect on the circadian system, as long as you're outside in the shade and it's a sunny day, 10 to 15 minutes should be ample amount. - Okay, and then let's say it's kind of overcast. It's not particularly bright or there's solid cloud cover, but obviously the sun is out, but it's not as bright.

How long do you think it would take to set the clock? - 10 to 15 should be sufficient. Stay for half an hour, stay for 45 minutes. If it's very dark cloud, yeah, stay for longer. (upbeat music)