The Strange Scourge of Light Pollution

In January 1994, a 6.7-magnitude earthquake
knocked out power in Los Angeles. In the following hours, emergency services
fielded an alarming number of phone calls from people asking if the big silvery cloud
hovering in the night sky somehow caused the quake. They were referring to the Milky Way. Which is maybe a little sad on several levels,
but not all that surprising. About two-thirds of Americans, and half of all Europeans, can
no longer see our own galaxy in the night sky. Why? Light pollution. It started innocently enough, eons ago, with
fire, and then oil lamps and candles, and then, not too long ago, electricity. Since the first electric street lights appeared
in the late 1870s, our world, indoors and out, has been awash in the glow of artificial
light. At this point it’s so ubiquitous that most
of us don’t even notice it until it suddenly goes out. Today we’ve got lights rigged everywhere
— buildings, billboards, streetlights, stadiums, yards, and parking lots. If you live in a city or even a suburb, it
can be hard to find any real darkness these days, let alone look up and see many stars. Of course artificial light isn’t evil. It’s
awesome. We all use it; it’s done a lot for us. That’s why we invented it and pay
lots of money for it. But much of our outdoor artificial lighting
has made life more difficult — and not just for frustrated astronomers and light sleepers. We’re starting to see just how dangerous
light pollution can be to our environment, our wildlife, and even our own health. [INTRO] Light pollution! Let’s define it as the
adverse effects of excessive artificial light, and it comes in lots of different forms.
Urban sky glow, for example, is the overall brightening of the night sky, caused by light
being scattered by water or particles in the air. It’s that bright halo that appears
over cities at night and keeps urbanites from seeing stars.
According to the International Dark-Sky Association, LA’s skyglow can be seen from an airplane
200 miles away. Light trespass, meanwhile, happens when artificial light falls where
it is unwanted, like how your neighbor’s floodlight shines directly onto your otherwise
nice and dark pillow. Glare occurs when super-bright lights aren’t
properly shielded and shine horizontally. It decreases visibility and even be dangerously
blinding at times. And finally there’s clutter, the general
bright, bombastic, and over-the-top combination of various light sources in over-lit urban
areas. Think like the Las Vegas Strip, or Manhattan. Clutter contributes to urban sky
glow, light trespass, and glare, and just demolishes any nighttime ambiance. You can measure a landscape’s night-sky
brightness, astronomical observability, and light pollution using an assessment scale
called the Bortle Scale. John E. Bortle created the scale in 2001 to
help amateur astronomers compare stargazing spots. The scale ranges from one to nine, one being
the darkest of wilderness skies, and nine being the dense inner-city skies that so frustrate
star-gazers. It’s easy to imagine how light pollution
interferes with our ability to study the sky. All that sky glow projects up as much as it
does down, and it makes it hard to see the more subtle lights and objects in space without
special filters. But all this extra light ruins astronomers’
nights in another way–it messes with their spectrographs.
Spectrographs are instruments that record how an object’s light disperses into different
signature color components. If you know how to read a spectrum of a celestial object,
you can determine certain things about it, like its mass, chemical composition, temperature,
luminosity, and just what the heck it is. This makes spectroscopy a vital part of astronomy,
and light pollution mucks it all up, in part because artificial light shows up as bright,
obscuring lines in those spectra. So the light that comes from mercury vapor
lamps, for instance, creates a specific “fingerprint” line associated with mercury, while metal
halide lamps leave markers for halogen gases that they use.
These lines break up and obscure the otherwise smooth spectra we see from celestial objects,
and they can be hard to filter out. And as you can imagine, astronomers find this
interference really annoying. But excessive artificial lighting is more than an irritating
variable for scientists — it’s also a huge energy suck. As much as a quarter of all electricity
worldwide goes to generating light. A 2008 survey in Austria found that public
lighting was the largest source of their government’s greenhouse emissions, accounting for between
30 and 50 percent. Powering the country’s nearly two million public lights consumed
1,035 Gigawatt hours of electricity and released over a million tons of CO2 in the process.
And we all know how destructive these emissions are to our environment. But the light itself
can also be a very powerful biological force. If you think back to your last summer night
on the porch, you’ll recall lots of creatures are inherently drawn to light. Many of those
animals get burned. Meaning, they die. Many flying insects swarm around streetlights,
which is great for industrious spiders who know where to build a web, but it can throw
off the balance of an entire ecosystem. Bats, for example, have different reactions to introduced
lights– some won’t cross into the light, while others use it to their advantage. When some Swiss towns installed new streetlamps,
the European lesser horseshoe bat suddenly vanished, because, scientists think, they
were outcompeted by all the more light-tolerant pipistrelle bats that moved in to hunt insects
drawn to the light. An innate attraction to light can be so strong
that it can sort of mesmerize certain song- and seabirds, who are drawn to searchlights
on land, and the bright gas flares of marine oil rigs. The poor birds circle the lights
over and over until they just drop out of the sky from exhaustion. This seemingly uncontrollable attraction is
known as positive phototaxis, and while there are lots of competing theories about what
causes it, we still don’t understand its origins. Meanwhile, hundreds of species of night-migrating
birds rely on constellations to navigate in the dark, and researchers speculate that bright
lights may short-circuit their internal guidance mechanisms, causing them to smash into lit-up
buildings, radio towers, and even each other and the ground. And, of courses, all that artificial light
can also disrupt organisms’ otherwise precisely timed biological clocks. For a few billion years now, life on earth
has evolved under a steady, dependable day-to-night schedule. Pretty much all plants and animals
and even a lot of microbes have adjusted their activities to the regularity of sunrises and
sunsets. But with widespread artificial light, some
birds think spring has come early and start breeding ahead of schedule, or migrate prematurely. Nesting sea turtles, too, seek out the darkest
beaches, which are becoming harder and harder to find. Hatchlings naturally gravitate toward
the bright, reflective ocean, but get easily turned around by the big, bright cabana lights
behind them. I could go on, you guys! Light pollution disrupts
the nighttime breeding choruses of frogs and toads, confuses lovestruck fireflies, makes
zooplankton more vulnerable to fish, and exposes a host of nocturnal animals to predators,
limiting their foraging and mate-finding time. And somewhere on the list is us! Humans need darkness, too. We need that balance
of light and dark in our environment to maintain our circadian rhythm — the physical, mental,
and behavioral changes within a 24-hour cycle. These rhythms greatly influence our sleep-wake
patterns, body temperature, and the release of hormones! The production of the sleep hormone melatonin
is regulated by a group of nerve cells called the suprachiasmatic nucleus, or SCN, which
sits in the brain just above the optic nerves, so it’s constantly receiving information
about incoming light. When it registers less light, like it usually
would at night, these cells ramp up the melatonin, which leaves you drowsy and ready for bed.
But without that signal coming at regular, somewhat predictable intervals, it can throw
the circadian rhythm out of whack. These cycle disruptions have been linked to sleep disorders,
depression, obesity, and seasonal affective disorder. But I think that we can all agree that a lack
of sleep is not that huge a deal, compared to cancer. Several recent studies have suggested that
prolonged exposure to artificial light at night increases the risk of certain types
of cancer, especially breast cancer and other types that require hormones to spread. Some
of these studies have shown that women who work night shifts have higher rates of breast
cancer, and in 2007, the International Agency for Cancer Research classified night work
as a “probable human carcinogen.” The good news, if you can see it, is that
of the many, many, MANY forms of pollution we face today, light pollution is one of the
most easily remedied. Simple changes in lighting design, materials, and zoning could go a long
way in limiting the light pointing up into the atmosphere. The International Dark-Sky Association has
developed guidelines to help cities like Flagstaff, Arizona — the world’s “first international
dark sky city” — to reduce light pollution. Their tricks include things like shielding
light sources so they point downward, limiting the lumens — that’s the unit we use to
measure perceived brightness — that individual lights can emit, and putting caps on the number
of lumens emitted per acre. Even Paris, the City of Lights, now requires
storefronts and office buildings to turn off their lights between 1 and 7 am. Not the Eiffel
Tower though, that can stay on. Standards like these can save communities
a lot of energy, money, and work toward restoring some ecological integrity. Not only that, getting a handle on this pollution
may give us back something vital to humanity– our ability to look beyond the smallness of
ourselves, out into the infinite beyond. It’s like what Neil de Grasse Tyson once
said, “When you look at the night sky, you realize how small we are within the cosmos.
It’s kind of resetting of your ego. To deny yourself of that state of mind, either willingly
or unwittingly, is to not live to the full extent of what it is to be human.” Thanks for watching this SciShow Infusion
— especially our Subbable subscribers. To learn how you can support us, just go to And if you have questions, you can find us
on Facebook and Twitter and as always in the comments below, and if you want to keep getting
smarter with us, just go to and subscribe!

100 thoughts on “The Strange Scourge of Light Pollution”

  1. cut down nocturnal electricity.
    now before judging, cut down all the obligatory stuff that society developed because power people expected everyone else to have nocturnal lights (like more work hours, nightime meetings and emails, and related unnacounted COSTS from all this busyness)
    now why not also cut stuff that we really dont need and shouldnt be valued more than the milky way sight and healthy nights (like late time tv).
    now wait for your ciccadian cicles resync.

    sure you still like nocturnal light that much?

    p.s. nighttime violence (roberies and stuff) also depend on economic devolpment turned faster due to nightlife… if it were just for that, we would need less lights (since we would still be inside locked doors, sleeping)

  2. I did a research project back in 2010 in high school and everyone thought i was crazy for picking that as a pollution to study in environmental studies

  3. hey guys, i've never actually seen the arm of the milky way in the sky. start a go fund me so i can go somewhere dark and see it

  4. My grandma lives at the Navajo reservation, and there are no lights there besides her house. As there are no trees either there, it's a perfect view of the milky way.

  5. "as much as a quarter of all electricity generated worldwide goes to generating light"

    shows graph with 25% of greenhouse emissions being related to electricity& heat

    while that doesn't change the fact that it's true that about 20% of that is lighting, heating and cooling rooms costs about twice as much energy

  6. When I went to Los Angeles for the first time with my sister I was actually shocked at how the sky constantly looked like it was still sunset. Literally the whole sky looked yellow. After midnight.

  7. I love how Hank Makes everything more interesting. He is so enthusiastic about science. 🙂
    I know that if I dim the lights in the evening or have fewer lights on at night, my son has an easier time falling asleep when he goes to bed.

  8. been saying for a long time that way too much money is wasted on lighting the streets that nobody drives on at 3 in the morning

  9. Light pollution, like noise pollution is something that most Americans don't care about. They expect everyone else to love their noise and bright lights.

  10. Turn off lights which are not in use and make security lights motion-activated. This should significantly darken the night sky.

  11. Idea: genetically modify humans to make them able to see in the dark better like cats. Then we won’t need as many lights

  12. Over the years I have noticed and their are a lot less insects flying around porch lites and street lites at night , and even no insects.

    When I say this.

    Humans give me blank look.

    Humans are stupid idiots.

  13. when you live so far north you won’t even need any lamp light in summer because it’t getting ”dark” at midnight…. can someone turn off the sun? 😫

  14. I am so lucky to live just a few hours away from the famed "Darkest Skies in the World" of Jasper National Park. I got to experience them once. I was on a road trip with my father and a couple siblings. We were in the middle of the park when the day was coming to a close so we decided to find a campground. They were all full so we were redirected to an overflow campground. It felt like it was in the middle of nowhere. Fast forward to when we were sleeping, I was woken up by the urge to go pee. I took a look around and could see all of the inside of the tent so I thought, "I shouldn't need the flashlight" and didn't bother looking for it. Took a step outside and what I saw was… weird. The best way I can describe it is like when you play a video game that goes into a dark place like a cave and gives you a limited view around the character. It was exactly like that, exactly like I was in a video game. I could only see a metre or two around me. Everything else was black until you looked up enough to see the sky. There you saw the black silhouettes of the tree and mountain tops, and the most stars you will ever see.

    I looked back at the tent and thought, "I can still see the ground and the outhouse isn't too far away. I should still be able to find my way around by looking at the ground and using landmarks of sorts to get there and back." I take about three steps and look back again… tent is out of sight. I look around and see nothing but dirt and gravel. No unique land marks to get around. "Yeah no, I need that flash light. I'm going to get lost." Turn back, find the tent, find the flashlight and continue with my business.

    Bonus note: That flashlight was like a freaking spotlight in that darkness. Really cool experience.

  15. I've never seen the Milky Way , I thought it's normal because no one has ever seen it. I live in the most densely populated island in the world

  16. I still remember returning home to the countryside of Norway after weeks in London. The stars! My stars! I spent hours outside lying down in a field just to look, I'd missed them so much. Now I live on an island far far from any urban skyglow, and it is glorious. I spend many a night sitting in my hot tub beneath the moon, or walking in the forests or down to the sea to stargaze.
    Light pollution sucks butt.

  17. Could anybody imagine New York City, Los Angeles, or Las Vegas completely dark at night? That would be just freaky.

  18. People always complain about not being able to see stars when all you have to do is drive somewhere where you can see them, people are so needy and lazy

  19. Got back from a trip to china recently and Xi'an's skyglow is CRAZY looked like the sun was going to rise about an hour or two after it set

  20. Well. I got a black eye when I got up to go to the bathroom and looking for the door in the dark I ran into the wall. Not my best moment. Coulda used a light

  21. So…its bad you say? One issue though. Take a look at a topographical map, everything above a certain altitude has to have a marker(light) else planes may fly into it, which is of course very VERY ungood!

  22. Petition the officials in your cities to install full cutoff LED street lights instead of the types that contribute to light pollution. Examples of street lighting that contribute to street lighting are regular LED street lamps and the misleadingly labeled fully shielded LED street lamps. An example of good LED street lighting that cuts down on light pollution is at

  23. Wow, that city skyglow covers some ground. I can't even see the full Ursa Minor constellation from where I am. I never thought of my suburban skies as "dense inner city" even though New York City is less than 20 miles away. I think my limiting magnitude is 3.5 for the northern sky/overhead and 3ish for east, south, and west…

  24. I see pretty well under the light of the full moon so maybe we should focus on putting our limiting ground brightness to that of no more than twice the full moon.

    Instead we've got these new LED lights that are so bright (probably because they use so much less power so why not install 5x as many, ugh…) that my camera's metering is similar to that of daylight when I'm under their glare

  25. Here's how people can help reduce light pollution:

    You can also find eco-friendly lighting here:

    There are also basic guides for what lighting is best for
    cities and residences, including outdoor lighting:,
    as well as a page for just businesses:

    Here is a page on how to identify if your community has a
    lighting ordinance, if it does, how to enforce it, and if it does not, how to
    advocate for it:

    Here is a way to deal with light trespass and effects by the
    local government:

    Here are some lighting guidelines and info for policymakers:

    And how to help the animals affected:

    Also a very interesting debunking on why increased street
    lighting doesn't actually decrease crime:

    Here's a very interesting page on how much light energy is
    being wasted:

    If you're a super sciency person, there's a database for
    scientific research specifically relating to artificial light here: There are apps to help combat
    overturned circadian rhythms, meaning you can work at night but still not mess
    up your circadian rhythm:

    Finally, these are places where you can visit near you that
    have good light stewardship (meaning you can actually see the sky):

    If for an absurdly tiny possibility someone from the
    government read my comment, this link is how to get certified as a Dark Sky

  26. A bigger problem than high light intensity is high color temperature at night. A 2700K light doesn’t bother me nearly as much as a 4100K light. A paradox is that so called “warm” colors have a lower color temperature than “cool” colors.

  27. I live in Largo, almost dead center of the worst light pollution of Florida—the Bay Area. It’s a real pain in the a$$. I enjoy astronomy and love to stargaze, so when the light pollution is so bad you can’t even see stars like Polaris, it’s a bit hard to fully calibrate your telescope, even with a light filter.
    There are even ordinances here about the light pollution, yet that stops ABSOLUTELY NOBODY.

  28. When I saw a star, I was like "Oh a star!" and I was amazed by it and soon enough I saw some of it's friends and I think it's the Orion's Belt and I went back to my house and I saw stars but it is so dim that no one could see it passing by. After that, I really believed that even if they are gone in your sight, they are still on your side, waiting for you to see a glimpse of them and remind you that they are still there.

  29. Uh, no, I don’t see the “destruction” caused by those emissions.

    But if you’re so worried about CO2 emissions, time to get on board with nuclear. Otherwise you are putzing around the margins.

  30. With the exception of some red lights to stop planes crashing into it, why does the Eiffel Tower need its lights left on?

  31. I live in rural SE Nebraska. Last week a friend, originally from Indianapolis, now living in Dallas, visited me. As we were walking after sunset he remarked on how 'starry' the sky was here.

  32. I didn't see the Milky Way that I can remember, but boy, traveling only a few dozen miles out of a British Columbia town like Hope you can see an unbelievable amount of stars.

  33. Light also messes with an animal’s coat. They shed and grow hair based on the length of the days, not the temperature.

  34. Dear scishow please tell how carbon dioxide is pollution. From what I know about carbon dioxide it is plant food. How can you attribute carbon dioxide to negative effects on plants and animals. Higher levels of c02 is going to make an acre of farm land more productive. Please explain

  35. LOL All the city dwelling global warming experts. GW is a scam. im not trolling i want to get off fossil fuel but for real reasons.

  36. I grew up in rural Manitoba, Canada, spending most of my life even farther north in remote land, and my boyfriend has rarely left Lima. I remember how in awe he was about seeing the sky when we traveled outside of Lima, his reaction was beautiful. Everyone in a city needs to know what the night sky looks like.

  37. I remember when I visited Sedona, Arizona and they also had a dark-sky policy. They use a lot of traffic circles to reduce the number of traffic and street lights, and the design of any necessary exterior light is better designed so it aims 90% of the light downwards to the ground. It worked pretty well because you could see a lot more stars (not all of them like you would if you outside of the city, however).

  38. I always complain about all this damn light pollution, lights at night should be off imagine the energy saved if every city in the us shut off lights between 1-7 am

  39. There's places along the beaches in Fla that will deliver a couple hundred little turtles to the light on your back porch at night to die.

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