Observing at Skyhound



Home   Deep Sky   Shallow Sky   Comet Chasing   Observing Handbook   Meet the Skyhound   Contact

Light Pollution

Causes and Cures

It's not only Astronomers who should care, and astronomers should be less pessimistic.

I am often taken aback by what I hear people say about light pollution.  Many non-astronomers have concerns about unnecessary government intrusion/regulation, and have come to see light pollution as an issue that only affects astronomers.  And worse yet-- many of my fellow astronomers have come to believe that fighting light pollution is a lost cause, particularly near major urban areas.  Happily, both of these points of view are uninformed.

What is Light Pollution?

Light pollution is the shining of light where it does not belong.  There are three kinds of light pollution.  I'll start with glare because it affects everyone equally, not just astronomers.  Glare is defined as stray light that shines into your eye.  Glare is one of those things we put up with at night because we don't realize how unnecessary the annoyance is and how much trouble it causes. We just accept it without question. Glare makes driving and walking at night difficult, sending people indoors and limiting their enjoyment of their community after dark.  

Light shining into adjacent property where it is not wanted is a called light trespass. The enjoyment of the night sky is not possible under bright lights,  whether it be by an amateur astronomer with telescope or a Dad who wants to teach his children the constellations.  

"The most important thing to know about light pollution is that it is completely unnecessary."

Finally, we have light that is needlessly sent into the sky where it scatters off particulates in the air causing the air to appear to glow.  We see this effect around any city (it's called a light dome) where stray light lights up the sky as if the moon were full, again making it impossible for people to see the sky in all its beauty.  It is an unfortunate fact that many people these days don't even know what a wonder a starry sky is.  

The most important thing to know about light pollution is that it is completely unnecessary.  Fighting light pollution is not about eliminating lights, and its not about telling people what to do with their own property; just as with excess noise, the property owner is responsible for the harm done when his light crosses the property line to harm the well being of others.  Fortunately, just like any other form of pollution, such a littering, the problem is easily remedied by making more responsible choices.  Good lighting choices often increase the amount of light where it is wanted because the stray (wasted) light is directed to where it is needed rather than into the neighbors yard, eye, or the sky.  Alternatively, with the light focused where we want it, the same area can be lit with a lower wattage bulb, saving energy.

What Causes Light Pollution?

In short light pollution is caused by careless outdoor lighting.  Take glare for instance.  Have you ever wondered why we put shades on the lamps in our houses?  Is it purely decorative?  No--the shades eliminate glare by diffusing the light so that it does not shine directly in the eye.  Similarly, people shine lights at the ceiling or wall rather than directly into the room.  The glare rule is simple: if you can see the light source directly then the light entering the eye is usually overwhelming it, causing discomfort and interfering with your ability to see.  This is true for everyone, but it is a particular problem for the aging whose eyes are more prone to the effects of glare.  The ironic aspect of glare is that by making it difficult to see, the response is typically to put in more/brighter lights!

Similarly, lights that needlessly shine into neighboring properties cause light trespass.  

Lights that needlessly shine into the sky overhead contribute to the glow seen above our communities.  Badly designed fixtures that spill light in all directions rather than directing it to a specific location are mostly to blame.  But we must also recognize that the root cause of many poor lighting choices is trying to light up that place "way over there" with a light "way over here."  I see this in my own neighborhood.  We don't have a lot of street lights and often people will install a bright floodlight on the side of their house pointing out into the driveway.  In order to light up the whole driveway some of these lights end up almost horizontal!  I chuckle and shake my head every time I see a neighbor walking in from their car shielding their eyes with their hands because the glare from the light makes it impossible to see where they are going.  But I am also saddened that when I take a walk at night I too have to shield my eyes and if the light shines into my yard it really bugs me that the enjoyment of my yard at night is greatly diminished by the glare.

How Can Light Pollution be Cured?

It's really very simple.  It's just a matter of not being careless--a matter of putting a little bit of  extra effort into our outdoor lighting choices.  It starts by being aware that the problem exists and what the solutions are.  

The primary solution is shielding.  A shielded light directs the light to the area you wish to light up, while at the same time keeping it away from places you do not wish to light up, such as the sky, your neighbors yard, or the eye of a passerby.   

Most lighting fixtures are purchased for their aesthetics or often simply because they are what is offered on the shelf at Home Depot, Lowes, or your local hardware store.  "I guess this will do", seems to be a common refrain.  Until we care about good lighting as a society, why should the manufacturers and retailers care about giving us good lighting choices?  Fortunately good lighting fixtures are available today in a wide variety, but you may have to look beyond the shelf at Home Depot (see the links at the end of this page).

As for lighting up the end of your driveway from your house, there are two solutions.  The best solution is to put in a light pole closer to the area you wish to light; if you wish to light a very wide area, several poles may be necessary. I know this may be expensive, but considering the many years you may be living at your home, the subtle benefits of eliminating glare will pay off in terms of your own comfort.  Note also that glaring lights pose a safety threat, not only to passing motorists and pedestrians, but to the safety of your family.  Without the glare everyone can see better at night, whether it be to see the toddler behind your car as you back out or an intruder approaching from the bushes.  The second solution is quicker and easier: a motion sensor for your light.  These lights are normally off, but when motion is detected, such as the car entering the driveway, they come on for a period of time.  Although much better than a switched floodlight that must be left on to be working when you arrive home, or all night if you worry about unsavory characters, you will still have to put up with glare when the light is on.  

As aging lights are replaced--both our community street lights and our own yard lights--if we simply make better choices our quality of life will be improved.  This improvement is not imperceptible.  We may one day wonder why we never noticed how ugly it was before.  A good example is my own community of Cloudcroft, New Mexico.  This is a small village that lights its streets with one of the worst lighting choices it could make.  For years these lights have shown into the sky, windows, and into the eyes of passing motorists or those out for a stroll.  But the simple addition of a Hubbell SkyCap (a shield) to the existing light fixtures in our shopping district made a difference that was difficult to miss, although I suspect many simply had a happier, more comfortable experience without ever realizing why.  Tourism is the primary economy here, and I am certain that the softer more effective lighting has put more people on our boardwalks after dark.  The bonus is that the light overhead diminished measurably, making Cloudcroft a better place for astronomy and for those on vacation who wish to have the chance to see a starry night sky (often for the first time).

As time passes it is quite possible that our grandchildren will one day be able to see a starry sky again from the city--there is no reason why they can't--as long as the light is simply directed only to were it is needed and nowhere else.   Is that so much to ask?

Purchasing responsible outdoor lighting: