Light pollution: the case of the missing stars

light pollution demo

The constellation Orion, imaged at left from dark skies, and at right from Orem, Utah comprising about half a million people.

In our industrial society, light pollution makes it impossible to see what the night sky ought to look like.

We have too many lights on at night. Most of them are brighter than they need to be, targeted poorly, and improperly shielded.

The Milky Way used to be so bright that it cast shadows on the ground. Now hardly anyone in the US can see it at all.

We can still see the brighter planets with the naked eye. They used to cast shadows, too. No more.

In 2001, John Bortle devised a nine-point scale for measuring darkness. Class 1 is how dark the sky would be if there were no artificial light present.

Today on a cloudless night, someone on the Empire State Building’s observation deck can see less than 1% of the stars that would be visible without all the city’s lights. New York’s night sky is Class 9 on the Bortle scale. Most American suburbs register at Class 5-7.

Class 1 skies have all but vanished from the continental US. Light pollution threatens remaining Class 2 areas. At the North Rim of the Grand Canyon, about as remote a place as is easily accessible, the glow of lights from Las Vegas shine brighter than the Milky Way. And it’s 175 miles to Las Vegas from there.

Sky glow, the brightening of the night sky, obscures the night sky for 80% of the world’s population—99% of the population in North America and Europe.

And sky glow is only one component of light pollution. Others include glare, light trespass, and light clutter.

Environmental consequences of light pollution

The negative effects go beyond obliterating our view of the stars.

sky glow, light pollution

Sky glow over San Francisco

Energy consumption

The US uses 120 terawatt-hours of energy every year for outdoor lighting, mostly for streets and parking lots. That’s as much as New York City uses for all purposes in two years.

We waste at least 30% of that energy by not shielding the light adequately. A properly shielded fixture will direct light down to the ground and not allow it into the sky. We waste additional energy with unnecessary light, especially in empty office buildings.

That much energy costs about $3.3 billion. Generating it releases 21 million tons of carbon dioxide. To offset it would require planting 875 million trees annually. Properly shielding all our outdoor lights would cut energy consumption dramatically.

Disruption of nature

Light pollution, clouds and snoe

Light at midnight, reflecting from the clouds to the snow

We haven’t quite turned night into day, but the night sky is hundreds or thousands of times brighter now than it was before the invention of artificial light.

The natural cycle of light and dark govern eating, sleeping, and reproduction of plants and animals. Light pollution especially disrupts nocturnal animals.

Here’s just one example: sea turtles hatch at night on a beach. The bright horizon over the ocean always showed them how to find the sea. But now artificial lights lure millions of them in the wrong direction, and they die.

Disruption of human health

It’s not just wild animals that depend on a natural light-dark rhythm. So does the human biological clock. Artificial light interferes with the body’s production of melatonin, a hormone that helps us sleep. It also boosts our immune system and helps our glands to function properly, among other things.

Blue light at night is especially harmful. And our computer screens and TVs produce it in abundance. And unfortunately, so do many LED and CFL light bulbs.

Issues of crime and safety

I have neighbors who have lights on outside all night. I suppose they think it makes them safer. I’ve always figured that they’re just making it easier for burglars to see what they want in the back yard at night.

Actually, most property crime occurs in the daytime. Vandalism, graffiti, and holdups occur at night, and lighting only makes favorable conditions for the criminals.

Glare from overly bright and poorly aimed lights can actually decrease safety. It can not only temporarily blind us, but make it harder for our eyes to adjust. Our eyes adjust to the brightest object in sight. Glare therefore makes it impossible to see much in the surrounding darkness.

In graduate school, I once walked to a party in a nearby, but unfamiliar neighborhood. I was surprised that streets with such expensive houses had no street lights, but I found my way. Recent studies produce no evidence that our street lights prevent either accidents or crime.

Lighting only helps deter crime if it helps people notice criminal activity when it happens and if it doesn’t light the way for criminals. It makes no sense to spend money shining bright lights where no one passing by can see, such as a back door. Security lights ought to have motion detectors control them.

Wherever they’re necessary or justified, they should be properly shielded and not produce glare.

What can we do about light pollution?

light pollution from space

Composite of hundreds of night-time pictures made by the Defense Meteorological Satellite Program (DMSP) in 2001

Most light pollution comes from street lights, lights at sports stadiums, lights in parking lots, and so on.

It is not properly shielded. Instead of shining on the ground where it’s needed, much of the light shines up into the sky.

Solving those problems will require governments and businesses to change their ways. Required changes include, but are not limited to, enacting new laws.

Arizona has darker skies than almost anywhere else in the country. In 1970, sky glow from rapidly-growing Tucson seriously interfered with astronomical observations at the Kitt Peak National Observatory, 56 miles away.

Two Kitt Peak astronomers persuaded Tucson to pass an ordinance to regulate outdoor lighting. Other cities and counties in Arizona passed similar laws.

Calgary, Alberta reduced its spending on electricity by more than $2 million annually about 10 years ago when it replaced its street lights. The new ones are fully shielded. The California Department of Transportation saved money by using passive guides like reflectors on highways. They concentrate light where drivers need it and require no electricity.

But I assume most of my readers don’t have a role in making decisions for governments or corporations. Do individual households and small businesses have a role?

Even the light in our homes, stores, and offices illuminates the outside when we don’t draw the shades. It’s one aspect of light trespass—light going where it’s not needed.

So don’t turn on any lights, indoors or out, that you don’t need. Draw the blinds or close the curtains in your house or office at night.

If you have lights on all night in your yard, turn them off. You get no benefit from them. If you’re concerned about safety, operate your lights on a motion detector, and set it so rabbits and other small nocturnal animals won’t trigger it.

And make sure to get proper shielding for whatever outside lights you use, including your porch light.

I mentioned earlier that our screens and even energy-saving light bulbs produce blue light that disrupts our sleep. Fortunately, light bulb packaging tells us the “color temperature,” measured on the Kelvin scale. Blue light can have a temperature of more than 5500ºK. Standard incandescent bulbs are about 2700º. Look for a color temperature of no more than 3000º.

Also, you can get color temperature apps for your computers, smart phones, and tablets. The Google search “blue light filter apps” found several lists of best apps for android. Add “mac” or “iOS” to the search for Apple products.

Maybe if we as a society get serious about light pollution, we’ll be able to see more stars. None of them are missing, after all. They just can’t shine in a bright sky.

The dark side: making war on light pollution / David Owne, The New Yorker. August 20, 2007
Light pollution / International Dark Sky Association

Photo credits:
Stars in a dark sky and Orem. Public domain from Wikimedia Commons
Sky glow. Some rights reserved by (matt)
Light reflecting on snow. Public domain from Wikimedia Commons
Americas at night. NASA photo at Wikimedia Commons

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