Saving the Night
Bright Streets, Dark Nights

By: Astronomer David Levy
Vail, Arizona

 Adapted from Parade Magazine with permission. 

        Far away in space, at the very edge of our known universe, a star has run out of gas. Without hydrogen to fuse into helium like our Sun, this star has been turning helium into carbon, then silicon and eventually iron.   Since iron will not fuse, the star has reached the end of its road.  In less than a second its core collapses, sending the rest of the star's matter hurtling into space in the awesome explosion of a supernova.
        As the exploding star shines with the brightness of a hundred billion normal suns, it sprays into space carbon and other elements that are the raw materials of life in the Universe.  Meanwhile its prodigious light pushes onwards, racing across the heavens at 186,000 miles per second for millions of years, passing other galaxies, until some of it forages its way into our own galactic system.   And after this incredible journey, a small amount of the supernova's light reaches Earth to tell its ancient story.

        But none of us will ever see this cosmic light show.  As the supernova's light reaches us it is drowned in a sea of a different kind of light, light of our own making, that lights up the sky and blocks our view of the night.  Both kinds of light use energy from stars:  the supernova discharges the energy of its own fusion, and our street lights burn energy from our Sun and fossil fuels, or from nuclear power.  The supernova uses its light to tell its story, but our lights shine wastefully into the night.  

Turning night into day

        If David Crawford of the International Dark Sky Association is right, Americans pour some two billion dollars each year into energy that does nothing but light up the underbellies of birds and airplanes.   All this money, spent unwittingly by industry, government, and by people trying to light up their back yards, is utterly wasted on light that shines uselessly into the sky. 
 
        The result is a squandering of one of Nature's greatest gifts to us-- the beauty of the night sky and the incredible events taking place within in.  A century ago, it was possible for most people to look up into the night and spot stars bright and faint, and even catch a glimpse of the Milky Way arching across the sky on a summer night.  No more: In most cities, outdoor lighting is so bright and full of glare that all but the brightest stars are dimmed.

        It doesn't have to be that way.  When light shines into the sky, it has no function other than to brighten the sky.  Such lighting does not make our streets safer, but it does prevent us from enjoying the night sky, picking out constellations, and following the planets as they travel through their orbits.  The problem is particularly acute for astronomers, who a few decades ago simply accepted the steady increase of city lights, and began to build their observatories on distant mountaintops.    We now know that badly designed lights are more than a nuisance to us; they can be lethal to migrating birds.  When some migrating birds, like warblers, fly low during bad weather, they have been observed to be distracted by light reflecting off low clouds.  The birds end up flying wildly like moths above the light fixture.

        Although we're much more conscious of the environment than we were a generation ago, unwanted lighting at night, and the wrong kind of lighting, is a form of pollution that most people are unaware of.   Although governments and homeowners opt for the brightest possible lighting, many lights are actually unsafe.

        The Problem of Glare

        Glare is the major problem with many outdoor lights.  Glare is what makes you cover your eyes to avoid the extreme brightness of lights so badly designed that they call attention to themselves rather than to what they're supposed to be lighting.   If the glare is severe enough, the shadowed areas will be so dark by contrast that the light actually becomes a hindrance to safety, providing shadowy havens where a crook can hide.   Outdoor lights are supposed to improve visibility at night, and a well-designed, glare-free light fixture is safer, and saves energy, dollars, and the night sky.   Without glare, you see better.

        "Unshielded" light fixtures are another common problem.  A light fixture should shine only where it is needed-- onto a street or in front of a house.  Lighting engineers call such shielded fixtures "full cutoff." Such lights do not shine into neighbor's bedrooms, or get wasted into the sky. After all, crimes are generally committed at street level, not thirty feet in the air.   Are you bothered by your neighbor's porch light shining into your window?  That's called light trespass, and in Australia, light trespass is illegal.  A number of U.S. cities and counties have "light pollution" ordinances designed to control where outside lights shine; some of the strongest codes are in Tucson, Arizona, and surrounding Pima County.  There, it is illegal to sell or use a light that shines higher than itself (lighting engineers call it above the horizontal, meaning that you shouldn't be able to see the light bulb itself from a building higher than the light.)  If a property owner's light fixture violates the code, the county gives the offending property owner a week or so to change the fixture, according to Lincoln Thomas, Pima County's Chief Building Inspector. After that, the county issues a citation.

        The effort to improve lighting has caught the attention of the Environmental Protection Agency, whose "Energy Star" program aims to help industry increase its energy efficiency.  Clark Reed, an Energy Star program manager, believes that sensible outdoor lighting is a part of this goal.  "Whenever anyone installs outdoor lighting that is energy efficient, the public wins twice," he says.  "Light pollution is reduced, allowing everyone to enjoy the night sky, and not as much energy is being produced at the power plant."

        The problem of light pollution goes well beyond a backyard.  Everyone who has tried to see the stars from a city knows that the night sky is disappearing as city populations grow.  This is a tragedy as great as if some great force swept the world clean of its deserts, forests, and oceans.  The darkness of the night sky is part of our natural heritage, and it is a shame that most of us will not see what was a birthright of earlier generations; the magnificent darkness of the night sky that lets us capture the distant rays of a supernova.  Let's hope you never have to tell your grandchildren that one day there were stars in the sky that everyone could see.            

The International Dark Sky Association

        Believe it or not, there is a large and growing organization whose sole purpose is to promote safe outdoor lighting. Founded by Tim Hunter, a radiologist and amateur astronomer, and David Crawford, an astronomer by profession, the International Dark Sky Association is a unique organization that wants to preserve the precious darkness of the night sky for us, and for generations in the future.

        The International Dark Sky Association leads a world-wide effort to stem the rising glow of the light that now blocks the night sky from most urban dwellers.  In Tucson, the success of the dark skies drive has been striking.  Although there are hundreds of more street lights than there were only a decade ago, the strength of the glow over the city has not increased by very much.

        To work toward its goal, IDA has a truly interdisciplinary membership that embraces astronomers, backyard sky-watchers, lighting engineers, light fixture manufacturers, architects, and anyone else with an interest in safe lighting.     The organization now has more than 2000 members worldwide; membership costs $30 a year.  For information, visit their website at http://www.darksky.org, or write them at 3225 North First Avenue, Tucson, Arizona 85719. 

Is your yard light safe?

        Try an experiment tonight.  Ask someone to stand in a dark place against the wall of your home, at the edge of the area lit by a yard light.    Now walk along the sidewalk past your house.  Can you spot the "intruder?"  If you can't, then your yard light is actually helping conceal him!

        In order for a yard light to do its job, it needs to light a wide area, but not so brightly that someone could hide in the shadows.  The lamp should be shielded, so that it directs light only where it is needed.  High pressure and low pressure sodium lamps are designed to reduce glare, and also cost less to run than traditional mercury vapor lights.

        What if your neighbor has a big bright light that shines into your window?  If you handle it well, this might be a good excuse to get to know your neighbor.  David Crawford of the International Dark Sky Association suggests that you begin positively, noting that he went out and bought a light to protect his home.  As your conversation goes on, you then suggest that the bright glare of his light might actually invite crime.  Because of the glare, the robber can see very well, thank you, but you as a homeowner can't see into the shadows created by the bright light.  Show him this article and suggest a full cutoff, shielded light that is much safer, and cheaper to run at the same time!

 How to be an expert in outdoor lighting

        *Good lighting fixtures often look like shoeboxes.  The lights within them are recessed, so they shine where needed.  These lights are increasingly popular in parking lots, and do not produce glare or light trespass.

        *Spherical glass globes are very bad, as most of their light is directed away from the areas that need to be lit for safety.            
 
*One of the most familiar light fixtures is a bottle-shaped glass, known as the NEMA light ever since it was endorsed by the National Electrical Manufacturer's Association decades ago.  A simple retrofit device, called "Hubbell Skycap" fits like a hat over the light.  The skycap provides full shielding and results in almost 50% more light on the ground within a hundred feet of the fixture.

        * When you're flying over a city at night, look carefully at the arrangement of the lights below.  If you can see well-lit areas but not the bulbs lighting them, then the lights are doing their job.  If you can actually see the bulbs, then they're lighting up your plane for no reason and wasting energy.  In Tucson, lighting control is so good that the few offending lights are easy to spot.

        * How sensibly is your state lit?  Highways in California and Arizona are lit with "full cutoff" shielded fixtures that are shielded and easier on the eyes that older models.

        *By far the most energy efficient lights are low-pressure sodium, or LPS.  They use only half the energy of bright blue metal halide lights, and never fade with time.  Although they cast a deep-yellow glow, businesses that use them have found that adding a very small amount of metal halide lighting gives an accurate color rendition.  Tucson uses LPS fixtures for residential street lighting, but like many cities, uses the brighter high pressure sodium (HPS) for major streets.