Dark sky bright soul
By Don Brett,
In a previous column we discussed how light pollution threatens mans connection to the natural world since it cuts him off from the night sky, a wonder that should always be as close as an upward glance. In this column, well look at some solutions.
As an environmental and potential health problem, light pollution is receiving increasing attention. A number of towns and cities in North America have created bylaws to help reduce light pollution. The most advanced of such municipalities is probably Tucson, Arizona as a result of lobbying from astronomers using the nearby Kitt Peak complex of telescopes. It is said that one can see the Milky Way from the centre of this city of 500,000, a remarkable achievement.
Closer to home, the District of Saanich, just north of Victoria, has passed a bylaw to reduce the light pollution affecting the Dominion Astrophysical Observatory. And the City of Calgary recently decided to replace all its streetlights with shielded, lower wattage fixtures in this case as a means of reducing electricity costs.
So how are these municipalities fighting light pollution? Fortunately, this environmental problem can be addressed with very low cost and effective measures. Most light pollution is caused by misdirected light. Through the simple expedient of properly aiming and shielding lights, a dramatic reduction in light pollution can be achieved.
Take, for example, the "cobra-head" streetlamp (Photo 1), millions of which have been installed to light roads and cities around the world. Due to the placement of the luminaire (the light source) within the fixture and the globe shaped lens, this fixture spews 20 per cent of its light upwards and another 20 per cent near horizontal, so that the emitted light hits the ground too far away to create effective illumination. (This horizontal light emission is what creates annoying, and dangerous, glare.)
The newer "shoe-box" design (Photo 2) provides the solution. The flat lens on the bottom combined with opaque top and side shields eliminate upward light emission and reduce horizontal emission dramatically. With a good reflector, this fixture can consume 30 per cent less energy while generating better illumination because glare is eliminated.
Another notorious source of glare and light trespass is the "wall pack" (Photo 3) that is frequently used for commercial and residential lighting. This type of fixture blasts more than 50 per cent of its output upwards or outwards rather than down. Again, the solution here is simple. Install a shield to eliminate the stray light (Photo 4). The shield should be placed so that only the target area is illuminated. Manufacturers are now making available many styles of wall lights with built-in shields.
I challenge you to do your own research on light pollution. The next time you are out at night, driving or walking, notice the lighting around you. Any time you can see a light rather than what is lit , you have identified a source of light pollution. (Think of the recessed pot lights in your home; you dont notice the light source, you only see the lit room.) Notice the glaring cobra-head streetlights and compare them to the well-shielded shoe-box design. Notice the commercial globe lights that splatter light in a 360-degree sphere, the wall packs, pole mounts and porthole lights) that produce uncomfortable glare and waste so much energy .
Now imagine a city employing shielded lights that direct light down so as to illuminate rather than obscure. Softly glowing street corners and paths are sufficiently lit for safety and security but no lights glare in your eyes. And when you look up, you can see thousands of stars.
In a subsequent column, we will look at Whistlers approach to night lighting.
Website of the Week
Royal Astronomy Society of Canada at http://www.rasc.ca . Lots of information on amateur astronomy. Look especially at the RASCs Light Pollution Abatement Program.