How to Time Light for Optimal Sleep & Wakefulness | Samer Hattar & Andrew Huberman
00:00:00.000 | (silence)
00:00:02.160 | - Assuming that most people wake up in the morning,
00:00:06.320 | as opposed to night shift workers, et cetera,
00:00:08.240 | we could talk about later.
00:00:09.400 | But they wake up in the morning,
00:00:11.200 | so let's divide the day into quarters.
00:00:12.600 | What is the proper way to interact with light
00:00:16.760 | in the first part of the day?
00:00:19.360 | - So I honestly think the easiest thing is waking up.
00:00:22.600 | Get as much light as you can.
00:00:24.080 | - Into your eyes.
00:00:25.920 | - Yeah, it's really nice.
00:00:27.200 | Your system is primed.
00:00:28.580 | If you're entrained, it's primed to get light.
00:00:30.640 | The sun should be out.
00:00:32.440 | Most animals in the wild,
00:00:33.800 | they actually seem to track the sun.
00:00:36.080 | The sun has a huge influence on life on Earth.
00:00:38.520 | It's actually, life on Earth is because of sun.
00:00:41.640 | So that's easy.
00:00:43.820 | In the morning, when you wake up, you need light.
00:00:45.800 | - Okay, so what is the behavioral practice
00:00:48.200 | that you recommend?
00:00:49.760 | Does it, let's say somebody is in a condition
00:00:51.920 | where there's a lot of cloud cover.
00:00:53.440 | - Yeah.
00:00:54.280 | - Is it important to get outside?
00:00:55.400 | - So I have to tell you,
00:00:56.560 | the cloudiest day is gonna be much more brighter
00:00:59.140 | than your room.
00:00:59.980 | You could ask any photographer.
00:01:02.080 | A cloudy day, unless it's really dark, dark clouds,
00:01:05.220 | usually cloudy days have much more bright outside
00:01:08.560 | than inside the room,
00:01:09.580 | even when you have good lighting inside the room.
00:01:12.480 | So I think in the outside is usually,
00:01:15.720 | even when it's cloudy, you're gonna get enough intensity
00:01:18.300 | to help you adjust your cycle to the day-night cycle.
00:01:21.480 | - So how long do you,
00:01:23.600 | these are general rules of thumb,
00:01:24.760 | but how long do you recommend people go outside?
00:01:27.040 | - So if you do it daily, you possibly need very,
00:01:29.680 | if you do it daily,
00:01:30.600 | because remember,
00:01:31.440 | this thing is gonna happen on a daily matter.
00:01:33.240 | So let's say 15 minutes.
00:01:34.080 | - So the clock is tracking it on a regular basis.
00:01:35.840 | - Absolutely, it's photon counting, it's tracking.
00:01:39.360 | I would say 15 minutes.
00:01:40.440 | If you don't do it daily, you may wanna increase it.
00:01:43.400 | And we'll talk about when you travel, what you could do.
00:01:45.480 | But yeah, 15 minutes should be fine.
00:01:47.760 | You do it more, it doesn't hurt.
00:01:49.640 | - And through a window, I was,
00:01:51.140 | my understanding is that through a window,
00:01:52.960 | it dramatically decreases the amount of light energy.
00:01:55.640 | - It depends of how, you know,
00:01:57.480 | how thick the windows are and how dark they are.
00:01:59.960 | So it's, but it's also nice to go outside
00:02:02.640 | and to feel the season.
00:02:04.240 | - Sunglasses off.
00:02:05.840 | - I don't use sunglasses.
00:02:07.440 | - But you have the Jordanian for pigment, you know, so.
00:02:11.600 | Yeah, whereas my eyes are very sensitive, right?
00:02:14.100 | - No, but I personally, you know,
00:02:16.880 | if I'm in the shade or if it's not incredibly bright,
00:02:20.000 | I try to, especially in the morning,
00:02:21.780 | but I'm also an early person.
00:02:23.360 | So we have to differentiate between early.
00:02:25.000 | - What time do you wake up?
00:02:26.000 | - I wake up at 4.30 in the morning.
00:02:27.560 | - But the sun isn't out yet.
00:02:28.640 | - It's not out yet, so it's.
00:02:29.880 | - So what do you do?
00:02:30.720 | You turn on artificial lights?
00:02:31.880 | - I usually don't turn on artificial light
00:02:33.960 | because I know the sun is gonna come up eventually.
00:02:36.300 | But that's why I don't like the change
00:02:38.720 | in the timing that they do.
00:02:40.800 | - Wait, but what do you do between 4.30 a.m. and 7 a.m.?
00:02:43.520 | - I mean, I just got my computer and my phone.
00:02:46.040 | So possibly I get enough light.
00:02:48.480 | But in reality, I mean,
00:02:50.080 | as long as you let your body get the morning sunlight,
00:02:53.580 | which I think is really, to me,
00:02:55.980 | and there's no evidence, but to me, this is,
00:02:58.780 | if you look at all animals, plants,
00:03:00.620 | this morning sunlight seems to be very important.
00:03:04.140 | And I, you know, we don't have experiments to show it,
00:03:07.160 | but I have a gut feeling that it has a huge impact
00:03:10.500 | on humans.
00:03:11.460 | - Well, Jamie Zeitzer's lab at the Stanford Sleep Lab
00:03:14.140 | has shown that these early morning light flashes
00:03:16.900 | can adjust the total amount of sleep
00:03:19.420 | that one will get and makes it easier to get into sleep.
00:03:21.860 | - Absolutely, absolutely.
00:03:22.700 | - Okay, so--
00:03:23.520 | - And Ken Wright also did this beautiful camping experiments
00:03:28.000 | that showed--
00:03:28.840 | - Right, maybe you should describe those,
00:03:30.360 | 'cause those are beautiful experiments.
00:03:31.600 | - They are beautiful experiments.
00:03:32.960 | He took these, you know, college students
00:03:35.680 | that had a late onset of sleep and late waking time.
00:03:39.400 | And then he said, "Let's go camping
00:03:41.000 | "and just don't use any artificial light.
00:03:43.460 | "And you could go to sleep as late or as early as you want
00:03:47.460 | "and wake up as late as early."
00:03:49.040 | And he found a huge shift in their sleep pattern
00:03:52.760 | just by exposing them to the light-dark cycle.
00:03:55.160 | I mean, so--
00:03:56.280 | - And it lasted.
00:03:57.400 | - And it lasted.
00:03:58.240 | - Even after they came back.
00:03:59.080 | - Exactly.
00:03:59.920 | - I think it was two days of camping,
00:04:00.740 | reset the circadian clock.
00:04:01.580 | - Seven days, but it lasted.
00:04:03.120 | Yeah, it's pretty amazing.
00:04:04.680 | Yeah, it's really incredible.
00:04:06.500 | - Okay, so get bright light of some sort early in the day,
00:04:11.160 | ideally sunlight, even on a cloudy day,
00:04:13.480 | it's going to be brighter than indoor light.
00:04:15.440 | - So that's easy.
00:04:16.320 | - Okay, so then--
00:04:17.360 | - And the other thing that I would like
00:04:18.800 | to mention to people, if you think it's very dim outside,
00:04:22.140 | let's say it's very cloudy, stay longer.
00:04:24.280 | So remember, intensity is only one component.
00:04:27.040 | Duration is also important,
00:04:28.600 | because remember that the circadian system,
00:04:31.260 | it's not like the image system.
00:04:32.720 | In the image system, you have to change every second
00:04:35.080 | because you're looking at different objects.
00:04:36.720 | You have to change your perception.
00:04:38.760 | But for the circadian system, it's trying to figure out
00:04:41.880 | where am I in the day-night cycle?
00:04:44.680 | So the more you give them the information,
00:04:46.740 | the better you are.
00:04:47.760 | So if it's very bright, you don't need a lot,
00:04:50.280 | because it's clearly going to make you fire like crazy.
00:04:53.440 | But if it's not bright, stay longer.
00:04:55.400 | Stay for one hour, have your coffee outside
00:04:58.440 | or something like that.
00:04:59.480 | It's just going to help.
00:05:00.960 | - I think you said something extremely important,
00:05:02.800 | which is that this circadian system
00:05:05.000 | is trying to figure out when you are in time.
00:05:07.960 | - Exactly.
00:05:08.800 | - Not where you are in space.
00:05:09.640 | - Sorry, I said where you are in time.
00:05:11.240 | I meant when you are.
00:05:12.320 | - Oh, no, no, I wasn't correcting you.
00:05:13.480 | I just meant that, I think fundamentally,
00:05:15.820 | that's the incredible thing about this system,
00:05:19.620 | that you have this clock, this 24-hour clock in your brain,
00:05:22.540 | but it needs to be synchronized to the outside.
00:05:25.300 | So could we go a little deeper
00:05:27.580 | into this circadian setting behavior
00:05:30.180 | and come up with some general rules of thumb?
00:05:33.060 | So let's say it's a very bright day, extremely bright.
00:05:37.000 | No clouds, sun's out.
00:05:39.280 | You said 10 minutes, 15 minutes.
00:05:42.540 | And I'll tell you, if you're sensitive,
00:05:44.780 | you don't even have to go in the sun.
00:05:46.460 | You could be in the shade.
00:05:47.860 | There's going to be so many photons out there in the shade.
00:05:50.980 | It's going to be perfect.
00:05:52.060 | You don't even have to see the sun.
00:05:54.100 | You don't have to have the sun.
00:05:55.900 | It's great for vitamin D.
00:05:57.060 | That's a different story.
00:05:58.020 | You could do this for your skin and protect your skin.
00:06:01.900 | That's not my area of expertise.
00:06:03.520 | But for that effect on the circadian system,
00:06:07.460 | as long as you're outside in the shade and it's a sunny day,
00:06:10.700 | 10 to 15 minutes should be ample amount.
00:06:13.300 | - Okay, and then let's say it's kind of overcast.
00:06:16.980 | It's not particularly bright or there's solid cloud cover,
00:06:20.680 | but obviously the sun is out, but it's not as bright.
00:06:25.020 | How long do you think it would take to set the clock?
00:06:27.100 | - 10 to 15 should be sufficient.
00:06:29.060 | Stay for half an hour, stay for 45 minutes.
00:06:31.500 | If it's very dark cloud, yeah, stay for longer.
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