Do these harsh, glaring lights look like those in your neighborhood or, worse, the ones in your front yard?
S&T: J. Kelly Beatty
We astronomers are engaged in a long, difficult effort to fight light pollution and regain our dark, starry skies. But do we practice what we preach? Take a look outside your home. Do your fixtures shine light into your neighbor’s window and toward the sky, or do they send all their light onto the ground? Can you see the bare bulbs from a distance, or are they shielded? Do you illuminate your house when no one is awake to admire it?
Reducing the glare from your home’s exterior lighting is a common-sense courtesy to your neighbors, who, like you, have every right to a dark bedroom at night. But it is in your best civic interest as well: to promote a safe, pleasant nighttime environment, many jurisdictions are passing laws that prohibit light trespass, rays that shine from one property onto another. What’s more, “dark-sky-friendly” practices will reduce your electricity bill. How? By ensuring that all your fixtures direct their light onto the ground, instead of spraying it up and all around, you can achieve the desired level of illumination with lower-wattage bulbs. Each watt saved means more money in your pocket.
A poorly directed, overly bright light (top) can spill light far from its intended target — onto your neighbor’s house or up into the sky. Shielded lights (bottom), especially those with “full-cutoff” designs, minimize glare and make your neighborhood safer and easier on the eyes at night.
International Dark-Sky Association
Home lights waste even more energy (and money) when they shine unneeded throughout the night. Let’s look at converting a 200-watt security light from continuous dusk-to-dawn operation to having it on only when triggered by a motion sensor. Shining all night, it will be turned on about 4,100 hours over the course of a year and use 820 kilowatt-hours of electricity, costing you $82 (at $0.10 per kilowatt-hour) in the process. However, the same light, activated by a motion sensor a few times each night, will shine for no more than about a half hour during darkness and use less than $4 in electricity annually. These remarkable savings recover the $20 cost of a standard motion sensor in the first three months.
Poor Lighting Increases the Chance of Crime
Beyond this needless expense, however, poor lighting may actually increase the chance of crime against your home and family. In its Recommended Practice Guideline 33 (issued in 1999), the Illuminating Engineering Society of North America states: “Too often people associate more light or brighter light with safer surrounds. It can be easily demonstrated that too much light, or poorly directed light, causes a loss of visibility.”
A classic case of light trespass. Strong, harsh light from poorly designed fixtures is streaming onto three neighboring buildings.
S&T: J. Kelly Beatty
When you look toward a glaring, poorly shielded fixture, the pupils of your eyes constrict in response to the bright light — despite being in otherwise dark surroundings. As even novice skywatchers know, your eyes then require several minutes to readapt before they can again see properly in the dark. Such glare can temporarily incapacitate your vision, making it uncomfortable (if not impossible) to view anything near its bright source. Worse, overly bright lights cast harsh shadows in which intruders can hide from view.
A shielded fixture with a lower-wattage bulb, on the other hand, disrupts your dark adaptation less and allows you to see more of everything around you. Arranging your home’s lights for evenly distributed illumination will minimize harsh shadows. And, of course, your eyes will adapt to the dark faster as you leave the proximity of your house.
Let’s face it: for most homeowners, an outdoor-lighting “makeover” is long overdue. With this in mind, we researched more than 20 manufacturers of residential lighting, talked to lighting contractors, and visited major U.S. retailers to create a consumer guide to purchasing dark-sky-friendly light fixtures.