Talieh Ghane researches the interaction between light and health at the California Lighting Technology Center. We talked about the biological vs. visual system of light, how to synchronize your circadian clock for better health, how light is like a drug, and why you shouldn’t be on your phone right before bed (guilty).

Can you give an overview of your research on how lighting impacts human biology?

Our body is confused—doesn’t know when it’s day and when it’s night—because during the day we don’t get that much of the intense light that you’re supposed to get if you’re in nature. And at night, when you’re not supposed to get any blue light, you get a lot of blue light.

We know that when light enters our eyes it travels through two separate pathways. For a long time scientists were aware of one pathway, the visual pathway that connects the retina to the visual cortex and helps us [perceive] the world around us.

Right now, [we know that light also travels] through this new set of photoreceptors called intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) and they contribute mostly to the biological pathway. The biological pathway sends a signal to our master biological clock (a very small area in the hypothalamus) and this clock needs to be synchronized with the cues it receives from the external environment.

The clock needs to be reset daily with a 24 hour day-and-night cycle. And if the clock is not synchronized, then our entire system is off.

One example is when we travel [through] different time zones. We have jet lag, we are tired and sick, and our whole sleep schedule, digestion—everything is messed up because our biological clock is running at the previous time zone, and then we travel to a new time zone and it’s trying to adjust itself.

When the retina sends information about the light in the environment to the biological clock, it resets itself and we get melatonin secretion, hormone production, our digestive patterns, our muscle strength, rest-activity cycle, core body temperature, immune response—everything is responding to the biological clock. And the whole thing is governed by signals from the light and the environment and how it synchronizes with the internal clock.

For millions of years, humans were exposed to sunlight in the morning and they went to sleep at nighttime. During the day we were exposed to the greater dynamic range of light [that] sunlight provides. We get different color temperatures and intensities of light throughout the day with natural light—with daylight.

And at night, human beings were not really exposed to high intensity light. Our main source of light [in] pre-history was the light from the moon and stars, which is really insignificant. Later on, we had fire and candles, which don’t really have that much light in the blue part of the spectrum. They’re more of a red light, which appears to be really insignificant to our biological system.

In fact, more than 90% of our time is spent indoors.

After 1880 when electric lighting was discovered, as humans we spend more and more time indoors. In fact, more than 90% of our time is spent indoors. We spend a lot of time at night at home: We watch TV on big screen LED TVs, we spend time on iPads, iPhones, and our computers late at night. And those have a lot of blue light—there’s more energy in the blue part of the spectrum—which our biological system is really sensitive to. Our body is confused—doesn’t know when it’s day and when it’s night—because during the day we don’t get that much of the intense light that you’re supposed to get if you’re in nature. And at night, when you’re not supposed to get any blue light, you get a lot of blue light.

So that’s why when we [see] the massive increase in the rate of breast cancer, prostate cancer, infertility problems, retinal degeneration disease, obesity problems, diabetes—those are known to be linked to the destruction of our biological pattern.

It might be too late when we finally realize what we have done to our bodies.

That’s actually what I’m fascinated with, and I think it’s really a public health issue. Right now a lot of the policies and the technology are [focused on] the visual effects of light and not really considering the biological effects of light—because we don’t see it, it’s not tangible. We don’t really know what’s going on and we can’t really quantify this light, so it’s very hard to pinpoint where the problems are. But we are starting to see all these issues. It might be too late when we finally realize what we have done to our bodies.

I have heard some information in the media about the health effects of blue light from electronic devices. Do you think the issue is getting enough publicity? 

I don’t really think it’s enough. I think receiving proper lighting throughout the day should also be a part of our lifestyle. It’s not just about proper lighting design, it’s also just little things that are important—we need to spend one to two hours in the morning under daylight. If we’re not receiving enough daylight in the morning, we should make sure that in our workspace, in our hospital [room], whatever space that we are confined to, we have high intensity, high CCT (correlated color temperature) light sources with high blue content. We need to have that kind of exposure for at least one hour in the morning.

And this is going to help our biological clock to be reset everyday.

There are multiple [studies] that show that effective lighting can really benefit healthcare outcomes. It reduces the cost of healthcare.

At night, if you need to study late or you have work to do late at night, there are tinted goggles that are orange or amber-colored that you can wear. Right now there are [also] different types of software that you can upload on your computer—f.lux is one of them. It changes the color of your screen so it takes some of the blue out. Apple recently added a night mode to the iPhone that you can program and after a certain time you don’t receive as much blue [light].

Also, we [should] change the policies. Right now, most commercial and industrial applications are transitioning from fluorescent to LED. But the industry is actually trying to replicate the same type of lighting that fluorescent was providing—it’s just the spectrum that’s changing. We are trying to get the same kind of lighting capability from the very dynamic light source that LED provides. We can tune the color temperature, we can tune the intensity, and we can program this system to mimic the spectrum of daylight throughout the day.

And I think [this is significant], especially in spaces where lighting is really important—my main research [has been] in a hospital setting. In a hospital, we know that patients are very confined to that space due to their physical limitations. They can’t really go out and they [are not] exposed to the outdoors or enough daylight.

We are trying to get the same kind of lighting capability from the very dynamic light source that LED provides.

In a hospital, you have a very consistent type of lighting throughout the day and night. They turn the light on when the nurse comes in to do their routine, their checkups. And that’s very uncomfortable for the patient and it also messes up their biological system. And if the patient can’t sleep enough, then they can’t recover fast enough, their medication doesn’t work as well . . . There are multiple [studies] that show that effective lighting can really benefit healthcare outcomes. It reduces the cost of healthcare. [Patients] are taking less pain medication when they are exposed to better lighting, the length of stay is shorter, and depression [decreases] in patients with dementia.

I think with LED lighting especially, in a space where people can’t go out to be exposed to good lighting, we can program it in a hospital setting to mimic the same kind of spectrum and similar intensity throughout the day [as daylight].

Is that what you would like to see in the future?

The process has already started. There are a few hospitals in Europe that are already doing this. Yes, this will be the future of healthcare design—I really believe it. It should be mandatory in hospital settings because it’s really key to the healing process of the patient, as well as the productivity of the staff: the nurses, the doctors. If you provide proper lighting in the nurse’s station at night they can be more alert and more productive.

Do you have any other tips for people who are trying to be healthier in the light they are exposed to?

Healthy lighting goes hand in hand with healthy darkness.

My best advice from what I learned in my research on light and health is that our biological system needs contrast. So it cares about the contrast [between] the light that you are exposed to during the day and the darkness that you are exposed to during the night. Healthy lighting goes hand in hand with healthy darkness. We need light during the day and we need darkness at night.

Have your room as dark as possible. Two hours before bedtime try to eliminate digital screens, TV—that should be a must-do before bedtime. And in the morning, even if you can spend 30 minutes of your lunchtime outdoors, spend some time outdoors, be exposed to high-level light and that can reset your circadian system, so you can sleep much better at night and be more productive [during] the day.

That sounds like really great advice. What about for someone who is on a night shift schedule? 

At nighttime our circadian system responds to pulses of light.

There’s been a lot of research about people who work the night shift. It’s possible to shift the phasing of their circadian system.

With a lighting prescription that a light and health specialist can [provide], we can change the phase shift of the circadian system [so] that [it] is in harmony with the work schedule. The problem is when you have rotating shifts—the rotating shift is worse because you get used to one biological cycle, and then two days after [that] you switch to a day shift and that destroys everything. It’s better to stay on a consistent night shift if you have to do a night shift.

For night shift workers, there’s a lot of research on what type of light you should give them. At nighttime our circadian system responds to pulses of light. During the day we need two hours of high intensity blue light (between 1 to 2 hours minimum) to reset our circadian system. At night time we don’t need continuous light, our circadian system responds to cycles, 10 minutes of bright light and then just regular light, and then another 10 minutes [of bright light]—in intervals. So we do four to five intervals of 10-15 minutes of bright, high intensity, high CCT light at night. That works better.

Would the ideal in the workplace be to program the system to match daylight?

The light that reaches our eye—that’s what counts.

The ideal would be mimicking daylight, that would be the best, healthiest option. What I’m saying is matching the dynamic nature of daylight: going from high color temperature (high blue content) to lower, and in the same way the intensity can also be dynamic. With daylight, the illumination is just too high for regular office hours. For regular office hours, between 300-500 lux on the task surface, that’s good enough.

But sometimes if there’s a budget problem, maybe in the office environment they can provide a lunchroom with skylights or high levels of blue light. So when people go in the morning to get their coffee or when they go to lunch, for 30 minutes to one hour they are exposed to a lot of high intensity blue light.

But in order for our biological system to be reset in the morning we need to be getting at least 600 lux at the cornea. The light that reaches our eye—that’s what counts. Sometimes we have a window in [our] office space, but if you are three, four meters away from the window, the intensity of the light that you get is not the same. So, that’s why in the office space—ideally, yes, you want to have very dynamic lighting, similar to what you are exposed to in nature.

But if that’s not possible, I think early in the morning getting at least one to two hours of higher intensity blue light. A lot of this can also be achieved—if the budget is the problem or the office space doesn’t want to change its entire lighting system—with personal task lighting. For example, doctors use light box therapy for depression, for people with SAD (Seasonal Affective Disorder).

What is a lighting prescription? Does it come from a lighting designer?

[W]e know that light is like a drug to the body. And just like a drug that you need a prescription for, how much you take, when you take it, what dosage, how many times a day, lighting works the same way.

Not really, no. Light and health is a very new field. There is still a lot that we don’t know. But based on what we [do] know, we know that light is like a drug to the body. And just like a drug that you need a prescription for, how much you take, when you take it, what dosage, how many times a day, lighting works the same way.

 

So the type of light that you receive, when you receive it, how many times a day, is it before—the marker for our circadian clock is our core body temperature—is it before your core body temperature [changes], is it after your core body temperature [changes]. The whole thing comes as a package. There are so many different factors that are important when we consider the non-visual effects of light versus the visual effects of light.

The visual system responds to light in a fraction of a second. But the circadian system is much slower in its response. It works as a cumulative response rather than a simultaneous response that the visual system has. And it cares about the intensity, the timing, the spectrum of the light, and it cares about prior history of exposure.

So for example, if you are exposed to effective light during the day [for your circadian system]—high intensity blue light during the day—you would be less sensitive to blue light at night. So even at night if you cheat and you’re working on your iPhone for half an hour before bedtime, your circadian clock wouldn’t be as disturbed as if you were not getting proper lighting in the morning.

The visual system responds to light in a fraction of a second.

History is important. So for a lighting designer, if you’re designing for, let’s say, a farmer, the farmer’s circadian system responds differently to light than a computer programmer who spends ten hours at the computer. So, that’s how history of exposure [comes into play].

So you’re saying that a lighting prescription might be something that a lighting designer might take into account when they’re designing light for a specific setting?

The amount of light that a young person needs to have their circadian system reset is much lower than the amount of light that an older person needs to get the same effects.

If you’re doing [lighting] for a hospital patient’s room, you can program the control system based on the age of the patient. If this is an elderly [patient] they need more light because the lens of the eye gets a yellow tint with age and it filters out the blue part of the spectrum that gets into the eye. The amount of light that a young person needs to have their circadian system reset is much lower than the amount of light that an older person needs to get the same effect.

If you’re doing the control system for a hospital patient’s room you can have a setting for older people and a setting for younger people. In the morning you can give them—the most effective time is two hours after waking—you can program it to expose patients to one to two hours of high intensity light.

And it can be changed. If the patient just came out of surgery and wants to sleep you don’t want to have that [light] on. It can be individually controlled by the patient and by the nurse.

And I know that right now a lot of people who are into lighting research, they do prescriptions for jet lag. So if you’re traveling they tell you exactly [what to do]—[they ask] when you arrive and what time zone you’re in, and they say, “Okay, so when you arrive you go under the sun for one hour and then you come back and then don’t open your curtains or do this.” And so they tell you exactly at what time you need to sleep so you can shift your circadian clock. It helps you to be in harmony with local time much faster.

Have you designed your own life to reflect your research?

No. Not yet. [laughing]

I think it takes time, and practice, and good habits. Right now, yes, if I don’t have a deadline, if I don’t have a presentation coming up, I try to eliminate blue light two hours before bedtime and I really see the difference in my sleep patterns. But I am researching all the time so a lot of nights I have to work till 3, 4 [AM]. Right now my lifestyle is not healthy at all. In the morning if I feel sleepy and I didn’t get enough sleep, I try to spend more time outside. I make sure that I am exposed to some sunlight on my drive to work. And I think that helps. I can feel on the days that are cloudy and I don’t get enough sunshine, I am a lot sleepier. And on sunny days I can see the difference.

What do you see for the future of lighting and what would you like to continue to research? 

I think the future of lighting eventually has to include the effects of light on human health and well-being. Just like energy-efficiency, at first a lot of people didn’t really buy into [it], because you have to spend more money to save just a little bit of money—by changing to an LED or energy-efficient lighting system. But eventually the technology wins and the price points drop down and more people are into energy-efficient lighting.

The same thing [will happen] with healthy lighting.

And for myself, I want to continue my research into the quantification of light for the biological system. That’s something that, in fact, I’ve started to do. We don’t really have a solid system to quantify light for the biological system and that’s because it’s a very complicated system. The way our circadian system responds to light is multidimensional, there are multiple variables that we need to consider. We have a lot of lighting systems that quantify light for the visual system. For example, you can say, “100 lux” and you have a sense of how much light it would be on a task. But when you say 200 lux for the circadian system, it can really be nonsense, because we can’t really visualize it or quantify it.

We have to come up with a new matrix to quantify light for the biological system. So we can say, “Okay, this light source provides 50 such-and-such units for the circadian system” and it’s either good or bad. That’s something that I’d like to continue working on.

[This interview has been edited for clarity and content.]

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