AMA Addresses Light Pollution

Researchers are raising several possible health concerns related to nighttime light exposure, among them a higher risk of cancer.

I usually think of light pollution as astronomers’ concern. Who else would mind if the sky glow is so bright that it washes out Orion? (When I can’t see Orion, I feel jilted — yes, even in the months when it’s below the horizon at night.) But the issue has a broader reach than my petulance. Fighting light pollution isn’t merely about seeing stars; it’s about being sensible in our usage and reducing waste.

Cheney in Times Square
Filmmaker Ian Cheney stands forlornly with a star wheel in Times Square in this shot from his documentary The City Dark. Light pollution is not just astronomers' pet peeve: a new report from the American Medical Association suggests that long-term nighttime light exposure could have health consequences.
Wicked Delicate Films
Still, I was surprised to see that the American Medical Association recently released a report entitled “Light Pollution: Adverse Health Effects of Nighttime Lighting.” It’s a review of some of the available research literature on nighttime lighting’s effect on people; it doesn’t present new research done by the AMA, although many of the results considered come from the authors' own work. The report covers a lot of ground, but it’s unclear what the review’s effect will ultimately be.

The document’s first human concern is glare, which report coauthor Dr. Mario Motta (Tufts Medical School) outlined for S&T readers back in 2009. Glare’s a pretty standard discussion topic in light-pollution conversations, in part because, as drivers age, their eyes become less able to cope with poorly directed light that scatters inside the eye itself. In 2009 the AMA passed a resolution submitted by Motta supporting the use of fully shielded lights, such as the flat-bottomed street lights. The new report reaffirms that resolution.

Vision researcher Gary Rubin (University College London) agrees with the report’s concern, saying the conclusions are “balanced, well-reasoned and thoroughly researched.” Disability glare — as opposed to “discomfort glare,” which differs from person to person — is definitely a problem for drivers, he says, noting that some cataract patients have had second surgeries to replace their new intraocular lenses with another kind that causes less nighttime glare. And as many of us know from experience, modern halogen and LED headlamps can make nighttime driving downright painful. (I can’t tell you how many times I’ve looked away from an oncoming car’s bright bluish headlights and thought, with scathing condescension, “Is that really necessary?”) Blue-rich light’s destructive effect on the molecule rhodopsin (a.k.a. “visual purple”) in the retina is what makes these headlights hurt so much.

But what really struck me was how much attention the reports’ authors give to serious health effects, particularly cancer. Several studies have concluded that women who mess up their natural day-night cycle by working night shifts on a long-term basis (such as nurses in a brightly lit hospital) were more likely to develop breast cancer. This natural day-night cycle, called the circadian rhythm, is a roughly 24-hour cycle our bodies follow to regulate things such as cellular processes and hormone release. It’s generally reset to match our environment by light that reaches specific photoreceptors in our retinas, signals that are then passed on to our brains. Usually that light comes from the Sun, but more frequently our bodies are taking their cues from manmade light sources.

Light trespass
Nighttime light can come both from inside — an active computer monitor, for example — and outside, shown here in a shot from Cheney's documentary film. So-called "light trespass" can be an issue when those around you aren't as careful with their nighttime light usage as you are.
Wicked Delicate Films
The evidence for shiftwork’s long-term risk is convincing enough that in 2007 the U.N.’s International Agency for Research on Cancer classified shiftwork that disrupts the circadian rhythm as “probably carcinogenic to humans.” The new documentary The City Dark also highlights the possible consequences of shiftwork in an interview with a nighttime shopping show host who later developed cancer.

One marker for circadian rhythm is a hormone called melatonin. (You may have seen it in the pharmacy’s sleep aids section.) Our bodies naturally make more melatonin at night and less in the daytime, but when exposed to enough light we damp down melatonin production, regardless of the “real” time.

As the new report acknowledges, what constitutes “enough light” is debatable. One 2011 study by AMA report coauthor and neurology specialist George Brainard (Jefferson Medical College) and his colleagues suggested that 90 minutes of nighttime exposure to 200 lux of fluorescent white light (equivalent to a moderately lit office) could drop melatonin blood levels by 30% — but so could only a few lux of blue light over the same period of time (melatonin production is particularly sensitive to the 450-480 nanometer range). Other studies have found a variety of effects, including a lack of notable effect. Mark Rea (Rensselaer Polytechnic Institute), director of RPI’s Lighting Research Center, suggests that 30 lux (think “modest twilight”) for 30 minutes is probably a good benchmark for when light exposure will start to affect melatonin levels.

Studies done by report coauthor Dr. David Blask (Tulane University School of Medicine) and others also suggest that melatonin fights tumor growth in rodents. But extrapolating that result from a nocturnal creature such as a mouse to the diurnal human is tricky. Melatonin levels and day-night ranges also differ significantly from person to person, Rea notes. He stresses that it’s still unknown how much of a melatonin drop might be needed to have serious health consequences. “That information just doesn’t exist,” he says. “I believe that melatonin is something you don’t want to squander, but extrapolating that to everybody’s daily life is unnecessarily dire.”

One of Rea’s major concerns with the AMA report is that it presents no specific measurements and therefore sets no threshold for what is and isn’t safe nighttime exposure. “You can say the sky is falling, but how much does it weigh?” he quips. He stresses that he’s convinced by Blask’s tumor work and the evidence for higher breast cancer risk in nighttime shift workers, but he wants to be careful about connecting the dots. “I’m against light pollution, I’m against breast cancer, I’m in favor of melatonin. Let’s just put them in the right order.”

Motta counters that there is now enough evidence to suggest that long-term melatonin suppression could lead to an increased risk for hormonally-induced cancer in people. “I’m not saying we go back to the Stone Age and not use nightlights,” he says. It’s not the brief exposures to light he’s worried about, either, or even delaying bedtime by a couple of hours. The problem arises when people are in “constant jetlag,” he says — living with confused circadian cycles and consistently suppressed melatonin. He hopes that the new report will push awareness of the importance of proper light usage.

The AMA review doesn’t distinguish between outdoor and indoor night lighting, but from poking through the research I get the sense that it’s the indoor light pollution that researchers are focusing on, not the pollution that keeps me from seeing Orion at night. On the other hand, Motta is also an amateur astronomer, and both he and Rea have successfully fought to limit outdoor lighting in their home neighborhoods. Inside vs. outside nighttime lighting is no doubt one of the issues that need further exploration.

Work is ongoing to expand our understanding of how light — particularly bluish light, like that from LCD screens — affects our melatonin levels. Some of the AMA report’s authors are among the leaders in this field. And a team led by Rea’s LRC colleague, Mariana Figueiro, is looking at iPads’ effect on melatonin and hopes to have those results out soon.

At Rea’s suggestion, I downloaded an iPhone app that measures the illuminance in your environment (yes, there’s an app for that) and tested evening conditions at home. I don’t know which wavelengths my iPhone camera is most sensitive to, but I figured a rough estimate was better than none. I held my phone beside my face and pointed its camera at my laptop, the overhead light turned on and reflecting off the bright screen where my Word document awaited my typing fingers. The meter registered about 200 lux, probably enough to suppress melatonin production if I sat at my desk late into the night. That rather made me glad that I turn off the computer at least an hour before bed.

15 thoughts on “AMA Addresses Light Pollution

  1. Mike W. Herberich

    In several cases known to me people do not constantly and exclusively do night shifts, but rather switch between day and night shifts every week or two weeks or so. Sometimes even between 3 shifts, early day, late day and night. This as opposed to exclusive night shifts would be another interesting point to be discerned in studies. I suspect that the outcome could be pretty different since it seems easier to me for a body to get accustomed to something very regular and lasting, rather than something constantly and irregularly switching. Another interesting point to me would be whether the number of lux are required to be applied uninterrupted in one stretch or rather could be in many shorter "flashes", all adding up to the same maximum limit.

  2. Bruce

    Unusual story Camile, but I’m glad you wrote it and S&T ran it. The part about those blindingly bright headlights is what I wanted to discuss. I thought that something was wrong with my eyesight, but your article shows that while it likely is worse for a person of my age, even a person less than half my age as you look to be has trouble at night looking into these new blue headlights. Your very right that it hurts, Camile. The driver’s equipped with these headlights must be pleased with the better view they provide, but if you’re driving around blinding oncoming drivers are you really any safer?

  3. K

    Do you really mean LED headlamps, or HID? LED headlamps exist, but are very rare, and I doubt you’ve seen a set. The HIDs are the bluish, blinding, obnoxious retina blasters you normally see in luxury cars.

    Thanks for a good article.

  4. S Catty

    Excellent article addressing an important issue. The connection between cancer and night time light exposure is an important one and has been largely overlooked in the 3+ years since I first read the research. If this were more widely known and publicized many people would not just turn off computers and lights at night but would be lobbying for reduced outside night-time lighting. Besides reducing potential cancers it would reduce costs to cities and home owners as well as benefiting nocturnal animals and the environment.
    Thank You

  5. Anthony Barreiro

    This AMA report course focuses on human health effects of light pollution. But biologists and environmental scientists have published a lot of research on the harmful effects of nighttime light pollution on plants and animals, e.g. migratory birds to name just one tragic example. I would urge every reader of sky and telescope to join the International Dark Sky Association, http://www.darksky.org . Unlike other forms of pollution which are very persistent in the environment, the solutions for light pollution are simple, inexpensive, and immediately 100 percent effective.

  6. carol gibson

    Bruce’s comment is so true. I’ve seen vehicles with as many as six of these bluish, glaring lights mounted on the front of their vehicles. When these are focused in the rear view mirror, it’s disorienting.

  7. Camille Carlisle

    To Owen: I just searched "illuminance meter" in the app store and picked the free app listed. To K: The researcher specifically mentioned LED headlights when I asked him about the glare issue, but you’re right, other types might also be problematic. Thanks for the comments!

  8. Phil

    Yes, alarm /is/ warranted. There is a long, long list of known drawbacks to excessive night lighting in the fields of safety, security, environmental lifeform effects, medical impacts on vision and hormonal disruptions (leading to cancer), and outright energy waste. There is precious little to recommend excessive night lighting.

    Remember the old discussion on Global Warming (now pretty much dead and gone)? Scientists dialed WAY back on their suggestions of harmful effects, for fear of being seen as alarmist. The results were twofold: the news was still suppressed by those with a vested interest in burning fossil fuels, and the results so far have been even worse than any responsible scientist was prepared to suggest would happen. We might as well get the news out, as any change to the status quo will be bitterly resisted.

  9. Mark

    Camille,
    Thanks for the update on the lighting issue. I live in southern Indiana and worked for nearly five years to establish a reasonable outdoor light trespass ordinance in our county.

    I took a lot of written and verbal abuse for the effort.

    I would like to see regional resources established where community conferences could be organized supported by medical doctors, community planners and concerned citizens to present the case for sensible outdoor lighting.

    I presented the argument for better lighting standards based on energy/cost savings, the fallacy that lighting up a property make it "safer" and my right as property owner to darkness without glare from a neighbor’s lighting

    While I think the IDA’s goals are laudible I find their arguments and approach much to esoteric and the question of impact on birds is absurd.

    I work in the communications industry and have for nearly 50 years. I currently maintain 8 radio transmitter sites. In those 50 years I have yet to find a single dead bird anywhere near a transmitter tower.

    How about some practical resources for sensible outdoor lighting advocates?

    Mark

  10. Mark

    Camille,
    Thanks for the update on the lighting issue. I live in southern Indiana and worked for nearly five years to establish a reasonable outdoor light trespass ordinance in our county.

    I took a lot of written and verbal abuse for the effort.

    I would like to see regional resources established where community conferences could be organized supported by medical doctors, community planners and concerned citizens to present the case for sensible outdoor lighting.

    I presented the argument for better lighting standards based on energy/cost savings, the fallacy that lighting up a property make it "safer" and my right as property owner to darkness without glare from a neighbor’s lighting

    While I think the IDA’s goals are laudible I find their arguments and approach much to esoteric and the question of impact on birds is absurd.

    I work in the communications industry and have for nearly 50 years. I currently maintain 8 radio transmitter sites. In those 50 years I have yet to find a single dead bird anywhere near a transmitter tower.

    How about some practical resources for sensible outdoor lighting advocates?

    Mark

  11. Mike W. Herberich

    I just listened to a radio program today that presented the fact: they, in principle and in the lab, succeeded in constructing head-lights that only shine where and when no rain drop is in the path of light (to diffract and disperse it). That, in principle, could take care of blinding glare once and for all … next to several other advantages.

  12. Alison

    Interesting article… and somewhat scary; as someone with Delayed Sleep Phase Syndrome, I am always up half the night — it’s genetic and I can’t manage to correct it. Goodness knows what my melatonin levels are :(
    If you HAVE to be on the computer late at night, get a pair of yellow-tinted glasses to cut down on the blue light. They can be found as "driving glasses" for cheap on eBay.

  13. hank

    A great resource — just one guy, with a very deep, very quirky personal website — is at LEDmuseum.

    Search the site for "spectra" — and hey, contribute something. You’ll see why.

    Craig’s posted a lot of spectra for LEDs and other light sources. I got curious and sent him a variety of what were supposed to be low-blue lights, to get a spectrogram to see what they are _actually_ putting out.

    They’re posted. Here for example, this "bug light" compact fluorescent filters out almost all the blue (below 500nm)
    http://ledmuseum.candlepower.us/eighth/gecflbl.gif
    Compare that to ordinary "white" CFLs or LEDs to see the difference. And those lights are quite comfortable for living under in the evening.

    Fluorescents — CFLs and white LEDs — are driven by emitting mostly in the blue end, and putting a phosphor coating that absorbs much of that energy and emits longer wavelengths.

    That’s not "color temperature" — very "warm" lights can still emit a lot of blue, enough to matter for these health issues.

  14. Hank Roberts=

    > impact on birds … transmitter tower

    Wait a minute, is that a robot post based on keyword detection gone wrong?

    It says it’s a response to the original article by Camille — but the original post says nothing about birds, and the only comment mentioning birds is about nighttime light impacting migration.

    The various effects of light pollution on birds are widely documented http://scholar.google.com/scholar?q=light+pollution+birds

    Nothing about radio transmitter towers and dead birds.

    By the way, that issue is also well represented in the literature. Few dead animals are ever found outdoors by people doing inspections, for any site for any reason.

    Yes, birds pile up under tall glass towers lit at night, but even there, the early morning collectors don’t get them all — the rats get there first.

    ——

    As to "nightlights" — there’s no need to go without -light- at night. Just go without -blue- light the last couple of hours of your evening wakefulness, and leave the no-blue-nightlights on at night to get around without blocking later sleep that night:
    search generally
    http://scholar.google.com/scholar?q=%22turtle+safe%22+light
    or more focused search:
    http://scholar.google.com/scholar?q=%22turtle+safe%22+AND+%22blue+light%22&btnG=&hl=en&as_sdt=0%2C5
    http://scholar.google.com/scholar?q=%22turtle+safe%22+light

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