Current mood: contemplativeLet's say you go out to water your flowers. What do you use? A sprinkler that you carry around? Maybe a one-inch green hose with a spray nozzle? Well, how about if you instead use a 100psi-rated fire hose? You do want to make sure they all get watered properly, don't you?
Insane, right? No, wait -- I forgot that the fire hose also has a leak right at the nozzle that sprays you straight in the face with a jet of water. Doubly insane, but the analogy is accurate when we tackle the topic of outdoor lighting. Looking around, I estimate that at least 80% of all outdoor lighting is overdone, misdirected, wasteful, and always does more harm than good.
In most cases, the outdoor lights we as a society have installed pour light as much sideways as down. The cobra-shaped public streetlight is a prime example. You can see them from a mile away, yet the amount of street that they actually illuminate well is fairly small, at best 200 feet away, beyond which any object fades into the shadows. OTOH easily 30% of the light goes sideways and even up, relative to the base of the metal fixture holding the bulb. Thirty percent of your tax dollars are lighting up the night sky. The wasted light may be close by, such as trespassing directly in a window, or lighting up the sky many miles away. Recall that our atmosphere scatters light, so all sideways light is "up" to someone, Either way, that, dear readers, is harm.
Even worse is the private yard light that looks like a crystal hornet's nest. These are everywhere. Fully 30% of their light, too, goes anyplace but down into the yard where supposedly needed. Same goes for those side-mounted box lights often found over doorways or on the sides of buildings, and floodlights pointed towards parking lots. Think fire hoses.
All of these lights typically draw 250 to 400 watts of power. At 10 cents per kilowatt-hour, or one cent per hour per 100 watts, a 250-watt bulb running 12 hours a day, 7 days a week, costs its owner $9/month, closer to $15 for the brighter ones, $28 if they run 24/7, as some do. Those fixtures, while inexpensive to purchase ($20), cost over $100/year to run. (Is that sirens I hear? Where are my flowers?)
I do not see where people get the idea that light glaring directly into one's eye is desirable, but any fixture that directs or allows light sideways as well as down is doing precisely that. It's nuts! The human eye works very nicely in dim-light situations, thank you, but not when nearby lights are bright. In fact it takes our eyes several minutes to recover from brightness when it is otherwise dark. Think leaky fire hoses.
The solution is to replace lights that shine sideways with ones that shine down. I know of areas which have both types of lights installed (Mars, Butler County, is one). It is actually brighter under the downward ones than the omni-directionals, though from a couple hundred feet away the omnis appear to be brighter. Further, the downward ones use far less juice, 50 watts, vs. 250, with whiter light than the omnis' peach-pink glow.
The point is, if you want the sidewalks to be lit, light the sidewalks, not the walls and roofs of every building in town.
Why is this important? First, cost. Whether you own the light, or run the business that pays for the light, or pay the taxes to whatever governmental body operates it, that's your money down the drain. Second, pollution. Much of that power comes from coal, and no matter how clean you make it, that's still smoke going up, as well as greenhouse gases.
Third, and this one is nearest and dearest to my own heart, is the loss of the night sky. That sideways and upwards light becomes the sky glow that blots out the stars in the sky. In a central city or the glare of a mall parking lot, you might be lucky to see 10 stars overhead, maybe 100 in a suburban yard. Dozens of miles out from the city, you might see 1,000. But in very dark areas, anyone with reasonably good vision should be able to see about 15,000 stars. If you cannot see the Milky Way, your sky has been wiped out by bad lighting.
Fourth is plain old safety. Those who want bright lights have bought into the very common idea that lots of light means security. Piffle. Define security! How secure are you when an attacker can clearly see you, and has positioned himself so that the nearby lighting is right in your face? How much better it would be if lighting were subdued so that your eyes were adjusted to the dark, with just enough downward light so that you can see not to trip over something!
How secure is your building from vandals who can see clearly what they're doing because you've provided them the light to do so? How safe is your yard when an intruder can see everything there, and hide in the shadows until people have left, before making a move? How much better if the place was always dark, but became flooded with light when someone walks in and trips a motion sensor? Light might make you think you and your property are safer, but it doesn't make you any safer.
The sensible approach to lighting is this: Less is better. Save money. Avoid waste. Avoid pollution. Think.
Use a sprinkler, not a fire hose, and don't spray yourself along with the flowers.
More info: International Dark Sky Association (or their resources page), and this link for one product anyone can buy and install.