Why Using an iPad at Night Disrupts Your Sleep. Podcast with Jeanne Duffy

Did you get enough sleep last night? If not, you are not alone. Self-reported sleep data suggests that most folks in industrialized countries are getting less sleep than we need.

One study that examined 669 American adults found the average sleep duration was just 6.1 hours, which for most people is simply not enough for optimal health and function. Short sleep is associated with a plethora of problems, ranging from impaired immune function, to worse glucose tolerance, to increased risk of traffic accidents. People who report less sleep tend to weigh more, and are more vulnerable to psychiatric conditions such as depression. So this is a really big deal!

Interestingly, community surveys suggest that the prevalence of inadequate sleep has been increasing in Western countries for some time. In the early 1900s, Americans were reported to average as much as nine hours of sleep per night – around 20-30% more than we are now!

So why are we getting so little sleep now? What has changed?

Sleep is complex, so it is likely that many different factors are coming into play here: Stress from work, long commute times, inadequate physical activity, misaligned eating patterns (late night trips to Taco Bell are not conducive to good sleep).

But the most powerful cue for our biological rhythms is bright light. As you may know, visible light regulates circadian rhythms by interacting with light-sensitive neurons in the eye. And our patterns of light exposure have changed dramatically over the past decades, due to the invention and ubiquity of artificial lighting. Unlike our ancestors, we can now fully control when and how much light we are exposed to, regardless of the time of day.

Many researchers are keenly interested in better understanding how the timing of our exposure to bright light influences the circadian system and our sleep. Which brings us to our guest for this episode.

In this episode of humanOS Radio, Dan speaks with Jeanne Duffy. Jeanne is an associate professor of medicine at Harvard Medical School and a sleep researcher at Brigham and Women’s Hospital. Her research has focused on understanding how the circadian timing system affects individual differences in sleep timing and structure.

Specifically, she has worked on some compelling studies investigating how alterations in the light environment impact sleep and circadian rhythms. In an earlier experiment, she and colleagues recruited 26 healthy participants to live in a lab for nine days. During this in-patient stay, the researchers calculated the time at which the subjects normally secreted melatonin in response to dim light. Once this was established, the researchers went in very late at night and exposed the subjects to a single pulse of very bright light for either 15 seconds or two minutes.

When the researchers re-assessed dim light melatonin onset, they found that these pulses of light induced a significant shift in their circadian rhythms, meaning that their body began secreting melatonin later than usual. The 15 second and two minute light light pulses caused an average phase delay of ~35 and ~45 minutes respectively. This finding suggests that very brief exposure to bright light stimuli (just 15 seconds!) can produce substantial circadian disruption.

But some might argue that an experiment like this is not representative of real-life light exposure patterns. It’s worth noting that the level of brightness of these pulses of light was 9500 lux, approaching that of sunlight or a therapeutic light box. That’s something that we pretty much never encounter late in the evening.

That’s why a subsequent study caught our attention. This particular study used a more ecologically relevant stimulus, something that many of us would regularly interact with at night: a tablet computer.

This paper was the initial impetus for our interview with Jeanne, so let’s quickly review what they did.

Duffy and colleagues recruited nine healthy young adults. Before the study, the participants maintained a fixed sleep schedule of 10pm-6am for one week, which was verified using Actigraphs (little wrist-worn devices that continuously measure activity and sleep).

Then, all subjects lived in light- and sound-attenuated research rooms at Brigham and Women’s Hospital for a total of fourteen days. Here’s how it went:

For one period of five consecutive evenings, participants were granted totally unrestricted use of an iPad. They were free to use it for emailing, surfing the internet, playing games, watching videos, reading. Whatever they wanted basically. They were also allowed to choose when they wanted to go to sleep – while knowing that they were required to be up by 6am the next morning.

For another period of five nights, subjects were given access to printed materials that they had brought with them to the lab (books, magazines, newspapers). Similar to the tablet session, they were given free rein to read as much and as long as they wished, and their sleep time was self-determined.

So what did they find?

Well, this is probably not too surprising for most of you reading this: subjects using the iPad at night showed major disruption in their circadian signaling. The usual rise of melatonin secretion was suppressed by more than 50%, and the timing of circadian rhythm onset was 48 minutes later on average. Importantly, this phase shift carried over into the night after the tablet sessions, when subjects were all kept in dim light. Participants also chose to go to bed significantly later when in the iPad condition – despite the fact that they knew they had to be up by 6am.

Finally, during the time that they were using the iPad at night, the participants subjectively rated themselves as being less sleepy in the evenings, but also less alert in the first hour upon waking up the following morning.

Taken together, we see that exposure to light through common light-emitting devices like iPads has an immediate suppressing effect on the secretion of melatonin from the pineal gland. But it also induces a lasting shift in the timing of biological rhythms, which influences sleep-wake patterns. And of course, since most of us have to be awake at prescribed times due to work or school or social obligations, this phase shift will usually translate to less sleep and poorer performance during the day.

Incidentally, this might be even more relevant in kids. New research suggests that the children may be even more sensitive to the effects of bright light late at night than adults, due to some age-related differences in the lenses and pupils. But none of us is unaffected.

Fortunately, there are some easy things that you can do right now to minimize the impact of LED screens on your circadian rhythms.

Tech companies have become more responsive to this problem, and have started to provide ways to mitigate the melatonin-suppressing effects of bright light, particularly short-wavelength (blue) light. One familiar example for Apple users is “Night Shift” mode, which enables you to filter blue light from your iPhone or iPad at night. But as you can see from the image below, altering the Color Tint can create an even better dark mode for your iPhone.

Here’s how it works.

Settings app → General → Accessibility → Display Accommodations → Enable ‘Color Filters’ → Slide Hue and Intensity to the max level.

Settings app → General → Accessibility → Scroll to the bottom of the page → Select “Color Filters” on a triple-click of the home button to turn on and off.

That’s just one relatively easy change you can make. Check out the interview to learn some more about how you can enhance circadian alignment, and about Dr. Duffy’s remarkable research on the subject!

Since we are on the subject of light, be sure to check out our courses by Greg Potter, PhD. In these courses, Greg explains how your biological clock works, and specific recommendations on how you can synchronize your circadian system. You may also find this past interview with Jamie Zeitzer on social jetlag to be helpful.

Have you considered becoming a Pro member of humanOS.me for $9.99 per month? When you go Pro, you get access to all our courses, tools, recipes, and workouts, and you also support our writing and podcast work.

If you think other people would benefit from listening to this show, you can help us spread the word by leaving a review at iTunes. Positive reviews really help raise the profile of our show.

Dan prepared for and conducted the interview, Ginny wrote the blog post, and Jeanne continues to do all the hard work in the lab!

Jeanne Duffy - 00:06: The activities that you're doing on the computer may, in and of themselves, cause you to stay up a little later than you would if you were doing something potentially less engaging, like reading a book, or a magazine.

Kendall Kendrick - 00:24: Human OS: Learn. Master. Achieve.

Dan Pardi - 00:33: Jeanne Duffy, Associate Professor of Medicine, Harvard Medical School ... welcome to humanOS Radio.

Jeanne Duffy - 00:38: Thank you.

Dan Pardi - 00:39: You have recently published a very interesting paper in the Journal of Physiological Reports, entitled, "Unrestricted evening use of light-emitting tablet computers delays self-selected bedtime and disrupts circadian timing and alertness." I look forward to speaking with you about this today, but before we get there, I'd love to know more about you and your research interests in general.

00:59: So to begin, how did you get into this field?

Jeanne Duffy - 01:01: I got into this field a bit by accident. I was attending Northeastern University, which is here in Boston, and their undergraduate program ... students typically spend six months in the second, third, and fourth years working full-time somewhere. They run a co-op program. I had done a series of co-ops in labs that were focused on analytical chemistry and microbiology, and I thought that wasn't what I wanted to do with my career. Then I was walking down the hall one day and there was a flyer on the wall and they were looking for people to volunteer to work in the lab that I still currently work in now. So I started volunteering in the lab as a technician when I was an undergraduate.

01:46: After I graduated, I left to travel and do some other things, but I was really captivated by the research, so when I was offered the opportunity to come back, first as a research assistant, I jumped on it. So I worked as a research assistant for a couple of years and then realized that I really liked it, and needed to go and get a PhD, so I went and got a PhD and I'm still here, many years later.

02:12: The lab, of course, has changed multiple times over the years, and the research has changed a bit, but I'm still doing sleep and circadian rhythm research, which I just find very fascinating.

Dan Pardi - 02:23: Thank you for that. Before we jump into this most recent study, which is just so relevant to how we are all living these days, you've done prior work that has been hunting down better understanding of how light is affecting us. So one study, "Circadian phase resetting by a single short-duration light exposure;" if you wouldn't mind giving us a little synopsis of what you found there, and what was the takeaway from that study?

Jeanne Duffy - 02:48: If we even step back further than that, when I was working here ... both before going to graduate school and as a graduate student ... this lab here was doing a lot of the basic studies in humans showing how the human circadian system responds to light, and how it responds to light at different times of day, and different wavelengths, and different intensities, and so forth. And the study that you referred to was one where we essentially put together what's called a phase-response curve to light.

03:20: The interesting thing about the circadian system is that it doesn't respond to light equally at all times of day. So if you give the exact same light stimulus in the late evening, what you'll do is shift the timing of the biological clock later. But you take the very same stimulus and you just apply it in the morning, instead of shifting things later, it shifts everything earlier. And then still again, if you take that same stimulus and you apply it in the middle of the daytime, you get almost no change in the timing of the circadian system. So the system responds in what we call a phase-dependent manner: It depends what phase you apply the stimulus for what result you're going to get.

04:08: To then understand how it responds at all different times of day, you have to do a whole series of experiments, where you apply the same stimulus at all different times across the 24-hour day, and then you look at the responses and you summarize them in something called a phase-response curve. That is essentially what we did in that study that you're referring to.

Dan Pardi - 04:29: I think this would be interesting for our audience. What are all the different elements of lights or timing that matter in the entrainment or modification of the circadian system? As we talked about, the timing of it does matter.

Jeanne Duffy - 04:43: Right.

Dan Pardi - 04:43: The intensity. What else?

Jeanne Duffy - 04:45: The wavelength or the composition of wavelength within the light, the intensity or the brightness of the light. And also what your previous light exposure history has been.

Dan Pardi - 04:57: Um-hmm.

Jeanne Duffy - 04:57: So if you've been at the beach all day and then you get an evening light exposure, you're gonna be less sensitive to that evening light exposure than if it was a cloudy winter day and you stayed indoors all day. So what's happened to your light exposure previously also then influences how you respond to light.

Dan Pardi - 05:16: Yeah, that's a really important point. I call it an anchoring effect of outdoor daylight to help that circadian rhythm entrain to when you want it to, and so that these light-emitting devices have less of an impact, perhaps, than if we were, like you said, indoor with just normal room light.

05:33: That's always surprising for folks, just the difference in light intensity between what seems to be totally adequate light that you're getting inside so that you can see perfectly fine, but then compare that with the intensity of light that you get when full sunlight exposure at midday. It's orders of magnitude difference, so.

Jeanne Duffy - 05:50: Yeah, and our visual system is so incredible that it can just operate across that incredible range of light intensity, that we don't even really perceive what a huge difference it is between ... I think the only time we perceive it is if you're outdoors on a sunny summer day and then you go inside, you realize you can't see anything at first, until your photo-receptors adapt to that dimmer indoor light and so yeah, we're usually unaware of those humongous differences in intensity between indoor light and outdoor light.

Dan Pardi - 06:23: So going back to that study that I had mentioned previously, you were looking at 15 seconds and two minutes of exposure. But what were the previous conditions that the person had been in, prior to getting that light stimulus? And then what was the effect of the light stimulus on sleep timing?

Jeanne Duffy - 06:38: In those experiments, similar to previous experiments we had done, looking at other aspects of light, we kept the individuals in dim indoor light prior to getting both light exposures. Typically, the structure of the experiment would be to bring the person in and have them, just on several baseline days in the lab and then do an evaluation of their circadian rhythm phase and amplitude in a procedure we call a concertine. This concertine typically lasts somewhere about 24 and 48 hours. That's carried out in very dim light. And then the person would sleep and then wake up, and that next day would be the day that they get the light stimulus. And again, the background light level would be very dim on that day, so they would have been in fairly dim or darkness for at least two, and possibly three days, before they got the light stimulus. We did it that way to be consistent between that particular experiment and previous experiments that we had done in the same way, but looking at other aspects of light exposure.

Dan Pardi - 07:49: What would you compare the environmental conditions to the listener, because interpreting light intensity can be hard. We don't know what light intensities are, but what would it be like? Maybe one lamp on but otherwise dark?

Jeanne Duffy - 08:03: The background lighting you mean?

Dan Pardi - 08:04: Yeah.

Jeanne Duffy - 08:04: First of all the experimental rooms are designed so that the light comes from the ceiling and is fairly consistent across the room, but it's maybe the equivalent of being in your living room in the evening with a couple small lamps on. In other words, it's enough light to see everything that's going on and to be able to read, but it's fairly dim light.

Dan Pardi - 08:30: Okay. That's useful. So you'd expect conditions like this to really maximize sensitivity to other light stimuluses that were coming in, right, because you didn't get that normal outdoor light that you would. Is that true?

Jeanne Duffy - 08:42: Exactly.

Dan Pardi - 08:43: Okay. And what did you find when under these conditions, it was again, 15 seconds and two minutes of exposure of these little pulses of light ... what did you find was the response to that even those brief light stimulus?

Jeanne Duffy - 08:56: With those very brief light stimuli, we could still measure small, but what we think were real, shifts of the timing of the circadian system.

Dan Pardi - 09:07: Right. What was the intensity of just the light pulses? So they're in a dimly lit room. They're in there for a couple of days, but then what was the intensity at the light burst?

Jeanne Duffy - 09:15: The light stimuli were on the order of about 8 to 12 thousand lux of light, and to put that into context, that is about as much light as there is shortly after sunrise or shortly before sunset outdoors. Much less than if you went outdoors in midday. If you go outdoors in the middle of the day on a sunny summer day, you may be exposed to as much as 100 thousand lux of light.

Dan Pardi - 09:43: So I'll just do a quick synthesis, you can tell me if I got it right. In this study, you kept the participants in a dimly lit room conditions that was the equivalent of maybe being in your house in the evening with a few lights on, enough that you could read, but not very bright. Then you gave them a 15 second or two minute burst of 8 thousand lux lights, which is like early morning or dusk lighting, so not midday, but outdoor light. And that was enough to cause a shift in their circadian timing system by 35 and 45 minutes, respectively. So I think what we see there is just even these pulses of light, when the conditions are right can cause the timing of the circadian system to shift.

Jeanne Duffy - 10:23: Yes, that's exactly right.

Dan Pardi - 10:25: Okay. Great. So that was leading up to the study that you've done now, which is very robust. It had these participants in for 14 days. How many subjects were looked at and what was the protocol?

Jeanne Duffy - 10:38: We studied nine people in the current study, and then actually follows on from related studies that we published a couple of years ago.

10:48: The protocol was to bring everyone into the lab for a two-week study. Each study began with us evaluating the timing of that individual's melatonin rhythm as a marker of the biological clock, and then they spent five successive days in one condition. I'll explain the conditions in a minute, but five successive days in one condition.

11:14: We then reevaluated the timing of their rhythms and also evaluated their sleep. And then another five successive days in the second condition, followed by another evaluation of their rhythms and sleep.

11:28: The two conditions in the current study were either just reading printed material, either books or magazines or newspapers in the evening, starting at 6:00 pm and going until at least 9:00 pm, or for the exact same time, in the other condition, using a light-emitting tablet computer. They weren't restricted to what they could do on that, so they could read or play games or do social media or check their email or whatever.

11:59: Around 9:00 pm, we did a few evaluations of their alertness, and then they were told that they could choose when they wanted to have the lights turned out to go to sleep at any point after that.

12:13: So we then looked at whether they chose to go to sleep right then or whether they chose to stay up later than that, and looked at comparing the two conditions and what they chose to do in those two conditions.

Dan Pardi - 12:26: Okay, great. So trying to keep the conditions as identical as possible, looking at markers of circadian timing ahead of time, doing some cognitive testing for sleepiness et cetera, around 9:00 pm, but the major differences were reading printed materials ... books, magazines, newspapers ... or using this light-emitting tablet, but they had to be using it for a certain amount of time, so that part was controlled. Then individuals could choose when they felt like going to sleep.

Jeanne Duffy - 12:55: Right. And just to step back, the previous study that we had done was quite similar, in that there were two conditions. There was a printed material condition and a tablet condition. The difference in the previous study was they could only read in each condition. So in the printed condition, they could only read a book and in the tablet condition they could only read a book on the tablet computer. And we chose the bedtimes in the previous study. So in the previous study, everyone read, either on the book or on the computer, from 6:00 pm until 10:00 pm, when we turned the lights out for everybody. And we found differences in the two conditions in terms of how long it took them to fall asleep, how much sleep they got, and whether the timing of their underlying rhythms changed.

13:41: And so in the current study, we wanted to understand whether without that constraint of telling them when to go asleep, whether there would be a difference in how long they stayed awake in the two conditions, because what we had found in the previous study was that one of the things that the light-emitting tablet does is it makes you more alert, and we think that's from the light itself. So we found that in that condition they were more alert in the evening, and so we wondered whether the fact that it makes them more alert would then have them choose to go to bed later.

Dan Pardi - 14:20: Right.

Jeanne Duffy - 14:21: So that's one of the reasons we did the second study.

Dan Pardi - 14:24: So between those two different conditions, you could see that the print materials, those are a little more passive, so you're reading either books, magazines, or newspapers, but with the tablet you could both read but also send emails and play games. Could some effects of delaying sleep time be because of the nature of the interaction versus just the light?

Jeanne Duffy - 14:45: Yes. That's exactly what we were thinking. We knew from the previous study that the tablet itself made the individuals more alert, and so we thought that might choose them to go to bed later, but we also thought that the other thing that's different, as you said, using the computer may also be more engaging. And just the activities that you're doing on the computer may, in and of themselves, cause you to stay up a little later than you would if you were doing something potentially less engaging, like reading a book or a magazine.

Dan Pardi - 15:18: Right. Let's talk about sleep first. What did you find between those two conditions on sleep?

Jeanne Duffy - 15:25: The first thing that we found is that the subject self-selected to go to bed later when they had been reading on the tablet computer compared to when they were just reading printed materials. It was around half an hour later that they were choosing to go to bed. Now they knew what time it was in both conditions, and they also knew that we were gonna wake them up at a fixed time the next morning. And so despite that, they self-selected to go to bed later.

Dan Pardi - 15:56: And since you were measuring melatonin as well, did you see that the light-emitting tablets had a different effect on melatonin than the newspapers?

Jeanne Duffy - 16:05: Yeah. So there's two differences. One is the direct effect that the light caused suppression of the melatonin on the evenings when they were using the tablet computer.

16:17: And then when we measured everything again the following evening, when everybody was in just dim light conditions to see what the cumulative effect of the previous five nights were, we found that the melatonin onset was significantly later after having used the tablet computer, compared to using the other printed materials. So light has a direct effect and it suppresses melatonin while you're using it, and then meanwhile it's also causing this shift in the underlying timing of your rhythms that is there even on the following nights when you're not using the computer anymore.

Dan Pardi - 16:54: Right. And so you'd expect that to have effect then on sleep architecture and awake quality the next day. Did you notice anything with differences in sleep architecture, aside from just the late sleep time for the tablet users?

Jeanne Duffy - 17:07: We didn't find any strong differences in overall sleep architecture. We definitely did find differences the next morning in how alert the two groups were. After having used the tablet computer in the evenings, those individuals were more sleepy the next morning, presumably because they both went to bed a little later and because even though we didn't find significant differences in the sleep architecture, there may have been subtle differences in the sleep architecture that made them feel more sleepy the next day.

Dan Pardi - 17:43: Yes, you could imagine by utilizing light-emitting devices, you feel like going to bed later, there could be some important changes in sleep architecture; the first one delayed sleep encroaching into total amount of sleep that you're getting. The second, having an impairment or changed to the sleep architecture even thought that was more subtle. And then third is the timing then of your circadian rhythm and if that is then determining your wake rhythm. Those three different factors that are going to lead to a harder day the next day by using those light-emitting devices. Would you agree with that?

Jeanne Duffy - 18:14: Yes. Absolutely.

Dan Pardi - 18:16: Yeah. Thank goodness it's so uncommon! Just kidding.

Jeanne Duffy - 18:22: Yeah, unfortunately it's not at all uncommon. And I think one of the biggest areas of concern is that the teenagers and even children are using these devices in the evening. So they're getting to be as sleep-deprived as adults are, and we know that you not only need sleep to feel alert during the daytime but sleep is so important we know for memory and for learning. And so if you're altering your sleep and disrupting your sleep by using these devices in the evening, for someone in that vulnerable age group where they need to learn so much and they're in school, it's probably impacting school performance as well. And there are some survey studies or epidemiology-type studies that suggest that may be the case.

Dan Pardi - 19:08: It's so interesting to me that the iPad tablets are used and that was really the first type of tablet that really exploded into the general population. It's not even 10 years old. It was introduced in the third quarter of 2010 by Apple, and of course there's different versions of tablets now, but within a very short period of time there was hundreds of millions of them sold. And so it's just a broader comment about how quickly life can change with the introduction of technology into our world.

19:36: And I think that we're now, thankfully, because of researchers like yourself and the work that you're doing, really having a greater appreciation about the impact of these light-emitting devices and even room lights and refrigerator lights et cetera, and how that affects how we feel that next day and how well we sleep. Are you planning on doing more studies like this to continue to hone in on the factors of these light-emitting devices and how they're affecting our physiology?

Jeanne Duffy - 20:00: We hope to do more studies like this. Right now we're preparing a grant application to be able to continue the studies. And some of those things that we would like to look at include software available that can alter the spectral composition that's emitted by the devices. We want to see whether by applying some of that it actually reduces some problems that we've noted, because theoretically it hasn't really been thoroughly tested yet. So we want to try that.

20:33: We also want to look at whether turning down the brightness of the screen as far as possible would also help.

20:41: And then we also want to do some studies where rather than being just in dim background lighting as a comparison for the control group or the groups reading on the printed material, to have both groups be in background lighting across the whole day that's similar to what people do in the real world. And we have a good idea of that because before our participants come into these studies, they wear a monitor that among other things monitors their light exposure levels. So we have a good sense of what typical light exposure levels in adults look like and we want to mimic that in the lab and see if you're in the more typical light exposure across the day, what's the impact of using these devices right before bed?

Dan Pardi - 21:27: I'd be interested to know is there a total time of exposure during the day that would then mitigate the effects of environmental light at night? What about timing of that stimulus; is it more important to get morning light and let's say, a half an hour or an hour of it? Those are interesting questions.

21:44: And then yeah, I think it's just part of good sleep hygiene to turn off lights that you're not using. I use programs that modify the intensity and the spectral composition or the tone of the light and even wear glasses that filter the blue light, so if I'm going to brush my teeth or opening the refrigerator, I'm not getting that pulse of more intense light right before bed.

22:04: I think that's one of the more interesting things for me is experientially finding what you've found in your study, that if I'm utilizing light-emitting devices, I just feel like going to bed later. And if I don't, then I'll feel like going to bed at least a half an hour sooner.

22:18: Well, thank you for doing this research and sharing the results with us. I think it's something that is affecting all of us in very profound ways. But it's also exciting because it's something that we can do something about and there'll be more work that comes out that, I think, shows us where to place our efforts. My intuition is that it'll be a balanced effort across the day to get the right type of light stimulus day, evening, and night, and look forward to seeing more work that comes out from your lab and others that help guide us in the right direction.

Jeanne Duffy - 22:45: Yeah. I think your point about how recently these devices were developed and how now ubiquitous they are, it's amazing to think about how rapidly they've been adopted and how often when we do things like this we don't initially understand what we're doing to ourselves by using them. And so, I think more research on how to mitigate the impacts of them are gonna help us, and hopefully help people to make sure that they get enough sleep every night, because we know it's important, not just for feeling good the next day but for all aspects of both physical and mental health.

Dan Pardi - 23:23: I work with a lot of audiences and one thing that I stress is getting exposure to what the feeling of really good circadian alignment and adequate sleep feels like. The competitive landscape is your device. It is an interest-delivering mechanism, because we self-select what we're reading, what games we're looking at, what videos we're looking at, and so it's something that's really pulling our attention with high interest. And you have to have this countervailing force of saying, "I really want to feel my best the next day," to prevent you watching one more episode of this show that is designed to hook you and keep playing them automatically.

Jeanne Duffy - 23:58: Exactly.

23:59: Yeah, and I think that's a good point that one of the interesting things that we know from our research and other people's research is that when you have disrupted sleep, and either insufficient or disrupted sleep and you have the same issue night after night, after night, after the first few nights you no longer remember what it feels like to have a really good refreshing night of sleep and to feel really awake the next day, because you're always comparing it to what happened yesterday.

24:29: And we see this in the lab all the time and when you do give someone a really good night of sleep then they suddenly realize what they were missing and what was happening. And so I think it's a really good point that it's an effort that we have to make, to make sure that we allow ourselves enough time to have a good night of sleep, just like we have to expend some effort to eat the right foods or to make sure we get enough exercise, to keep our health in top shape.

Dan Pardi - 25:00: That's what my company humanOS is all about; we call it a personal health mastery platform. Nobody's gonna make more efforts that affect your health than you will, and light is a great example for it. You are going to be the one that makes more decisions about food. You're also going to be the one that's going to have the greatest influence on the type of light exposure that you are getting across the 24 hour period.

25:21: With some knowledge we can self-direct in a more effective way. I mean, the nice thing about sleep ... I always joke around when I speak with folks is that with food the thing is: Don't eat that food that you love. But with sleep it's: Okay, do more of this thing that makes you feel amazing the next day.

Jeanne Duffy - 25:37: And it's so easy, right?

Dan Pardi - 25:40: The rewards are immediate.

25:41: So there is possibly this response from light coming into the eye that directly stimulates cortical arousal that keeps you up. There's also the light effects on circadian timing. What are some of the easiest interventions? And yes, perhaps utilizing these tools within our technology that modify the spectral composition of the light, so things like F.lux or wearing blue-blocking glasses. Those are interesting.

26:05: What about taking 300 micrograms of melatonin at the same time every night to initiate that dark signal pharmacologically?

Jeanne Duffy - 26:12: That's an interesting question. I think we don't know how those two things would compete against each other and which one might win out. So in other words, if you were taking the melatonin and you were still using the device, which one would win? I'm not sure that the melatonin would cancel out what was going on with the light from the device.

Dan Pardi - 26:34: I'd love to see a comparison of that, because for a lot of people, they're willing to try to do ... what are all the things I can do to feel my best, but for another broad spectrum of group it's: What's the easiest way to get improvements in outcome? So hopefully your tests will include maybe a comparator of a small amount of melatonin at the same time somebody puts on glasses. I think that would be quite interesting.

Jeanne Duffy - 26:53: It's an interesting question, yeah.

Dan Pardi - 26:55: Well, Professor Jeanne Duffy, thank you for your time. I really appreciate it, and it's been delightful to speak with you about your work and this important area that we can all take action on now.

27:04: More research will come that will give us more confidence about what we can do, but if you want to be at the cutting edge ... and what I like about it is: it's pretty low risk if you wear some glasses at night that filter blue light and you turn off your devices, it's a low risk intervention, even if we're still learning more about the impact of these types of interventions on our health and our sleep and our next day performance.

Jeanne Duffy - 27:24: Yeah and I think it starts with just appreciating that these things do have effects on our physiology, and so once you recognize that then you can start to figure out ways to again, minimize the negative aspects of those effects. So it's been interesting to talk about it. I'm glad that you're interested in it and will hopefully stay tuned for more studies that we're gonna be doing to tease apart more of this puzzle.

Dan Pardi - 27:49: I definitely will, and as you publish those, you can probably expect an invitation to come back and talk about it.

Jeanne Duffy - 27:54: I'd be glad to. That would be fun.

Kendall Kendrick - 27:59: Thanks for listening, and come visit us soon at humanOS.me