Dan Pardi
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We live in a time where immensely powerful technology has been completely embedded into the fabric of our everyday lives. And a visceral illustration of technology's power is spaceflight, where we literally transplant a human body off of our planet and into the microgravity environment of outer space. But living in space for just one month causes really serious health ramifications, from the dramatic loss of bone density and muscle mass and blood volume to the reactivation of latent viruses. There's really no part of the body that goes untouched when we put it into an environment to which we are unfamiliar. We don't think of gravity as a key part of our health, like diet and exercise, but clearly it is. So play a game with me here. Imagine that we created clothing that would allow us to adjust our relationship with gravity here on Earth. We would wear those clothes. We would feel lighter, we could run faster and farther and jump higher, and there would be all sorts of advantages, but there would be consequences too. We would now need to make sure that we were getting enough gravity in our day so that we didn't succumb to the same effects as these astronauts. I'm not here to talk to you about gravity per se, but it does speak to a fundamental truth. The successful functioning of the human body depends on a variety of environmental signals, and when those signals change, it poses a really serious risk to our health. And I am going to talk to you about one of these powerful health signals today: the signal of light. [A Powerful Factor in Health] And to do this, we can look to contemporary hunter-gatherer populations. Now, these are people that live without electricity, so they are exposed to light only in the forms that you see in nature. In the study of some of these populations, it's been observed they get their peak light exposure between the hours of nine and noon, at which point, they will seek shade during midday to get out of the intense heat. And at night, they're exposed to light only in the forms of fire and stars and the moon. [Natural Light Pattern] And like our relationship with gravity has been for our entire lives, humans' relationship with light had remained constant for millennia, all the way up until 1879 when Thomas Edison patented the incandescent lightbulb. Now, incandescent light gives off a warm tone of light similar to that of sunset, and these bulbs can be dimmed, but they are energy inefficient, rightfully worrying policy makers about their contribution to global warming. And so in attempts to be more efficient, humans were introduced to compact flourescent lighting, and these cannot be dimmed, and they give off a strange signature of light - only certain blues and greens and oranges are represented in their spectrum - and they flicker, causing headaches and fatigue. Then in 1992, the Japanese invented light-emitting diodes, or LEDs, and these had all sorts of benefits. They are energy efficient, they can be dimmed, and they are bright. And we find them not only in lamps but also in our screens, like high-definition televisions and our smartphones. And for the first time ever, from electric light, we could generate full spectrum white light. Now, when you filter out blue from full spectrum white light, we see the tone of sunset and fire. Now, all of this lighting technology has fundamentally changed the way that humans live. We now spend 90 percent of our time indoors, and according to a survey by the National Sleep Foundation, nearly all US adults have a screen in their bedroom and use those devices within an hour of going to bed. Compared to our ancestors, we have less sunshine, we have longer periods of light within a 24-hour day, and correspondingly, less darkness, and we get strange tones of light for a given time of day. For instance, you can get a full spectrum daytime signal right before bed. But does all of this matter to our health? And the answer to that is an unequivocal yes. We know that sunshine has a powerful effect on the synthesis of the hormone vitamin D. And it is now estimated that nearly 75 percent of the United States and over a billion people worldwide have low vitamin D status. We also know that sunshine is important for the synthesis of nitric oxide, which is involved in the regulation of blood pressure, which might be part of the reason why average blood pressure levels rise linearly the farther you get from the equator and why blood pressure rates tend to be higher in the winter than they are in summer months. But our brain is affected too. Animals that are kept in constant dim light conditions have 30 percent reduced capacity of key memory centers in the brain. And this translates to absolutely terrible performance on memory tests. When those animals are switched back to natural lighting conditions, those memory deficits are reversed. And perhaps most surprisingly, it's recently been discovered that our fat tissue contains light receptors. When sunlight is shined on these receptors, it causes the fat cells to shrink, to store less fat and to become less inflamed. And the authors of this research speculated that they might have just stumbled across a mechanism designed to increase fat storage during winter months, which is particularly interesting in light of the fact that we spend all of our time indoors and are nearly always fully clothed. So we see that sunshine is important for hormones, for blood pressure, for brain performance and for the regulation of fat. And I can assure you this is not an exhaustive list. But it's not the only way that our light environment has changed. We now get full spectrum white light after sundown, and it's having a dramatic effect on our sleep. Evening bright, white light associates with a reduction in total sleep and sleep quality, both of which associate with an increase in daytime sleepiness and reduced cognitive capacities the next day. And so it will now come as no surprise that children that have a screen in their bedroom perform worse in academics at every grade level tested compared to children who do not have a screen in their bedroom. And sleeping in darkness is important too. Adults that sleep with just a little bit of light on in their room are far more likely to experience symptoms of depression, and animals that sleep in dim light gain 50 percent more weight than their counterparts who sleep in darkness, even when they eat the same amount of calories. And so, as I was learning about all of this information in my work in the Zeitzer Circadian Biology Lab at Stanford and my work to optimize human health and performance, I started to become obsessed about how I could adjust my relationship with light so that I could maximize its benefits and minimize the negative effects of the wrong type of light at the wrong time. And to do this, I aimed to maintain a smart daily light rhythm - day, evening and night. This is a color temperature scale. Color temperature is measured in the units Kelvin. 1,000 Kelvin is the tone of fire. 5,000 to 7,000 Kelvin is full spectrum white light. And after 7,000 Kelvin, the light tone tints blue. And so by choosing the right LEDs, or LEDs that can adjust their tone, I was able to create a internal light environment that was reflective of what was happening outside at a given time of day. Here is my office at 4,000 Kelvins at 8:00 am, 6,000 Kelvins at 1:00 pm and back down to 3,000 Kelvins by 7:00. And in my bedroom, an hour before going to sleep, the light temperature is 2,000, which is, again, the tone of fire. But lamps are not the only way that we are getting electric light, and so I've also made adjustments to my screens. Either through modifying settings or installable apps, you can have it so that the blue light is pulled out after sundown. Now, I haven't only modified my bulbs, I've also modified my behavior. Morning light has been shown to increase the restorative nature of sleep at night. And so my morning motto is "get up, get out." Overall, I aim to spend at least 10 minutes outside before noon and at least 30 minutes outside every day. Now, what is the first thing people do when they step outside? Put on glasses. Well, I stopped wearing sunglasses. And instead, I started to wear special glasses in the evening to block out blue light from random sources like opening the refrigerator. And it has been shown that wearing blue-filtering glasses in the evening will naturally make people want to go to bed over an hour earlier than they usually do. Now, this might seem like a lot of information to digest, but we can keep it simple. Seek natural light rhythms - day, evening and night. Get outside when you can. And work to have your indoor spaces reflect what is happening outside. And this can be as simple as turning off lights that you're not using in the evening or dimming them to something more sophisticated, as I've mentioned today. Yes. We live in a world with immensely powerful technology, and it's only getting stronger and more invasive and more immersive. And the more the technology pushes us to live in a manner that is disconnected from the origin environmental conditions from which we came, the more that we need countervailing technology and strategies to help us stay human in the digital age. Societally, we have not fully embraced the powerful effects that light has on our health. But I can envision a day soon where human-centric natural lighting is the standard for all of our urban areas and our homes and the default settings on all of our devices so that we get something closer to the natural light signal that the human body needs to thrive. Thank you. (Applause) (Cheers)