Photo by Benjamin Williamson
Q: What are “dark sky friendly” exterior fixtures?
A: Sounds like an oxymoron, right? Outdoor lamps are there to illuminate the darkness, helping us move around safely. But in so doing, many also allow light to escape into the night sky, a phenomenon known as light pollution that masks our view of the stars. In fact, an international group of scientists recently determined that the Milky Way is invisible to more than one-third of the world’s population, including nearly 80 percent of North Americans. Light pollution also contributes to energy waste, disrupts many ecological processes, particularly for nocturnal animals, and can have a negative impact on human health, interrupting sleep and causing headaches, stress, and anxiety.
In 2008, Bar Harbor — home to Acadia National Park, one of the most blissfully dark places on the eastern seaboard — passed an ordinance regulating outdoor lighting on all new construction in town. To comply, fixtures over 1,800 lumens must be “dark sky friendly” — i.e., have casings or canopies that shield the bulbs, preventing them from being seen from above. Other cities and towns, including Portland, have their own ordinance requirements for lighting; check with your municipality to find out what the rules are.
No matter where you live, I recommend choosing warm (no more than 3,000 Kelvin), dimmable LED downlights, like those described above, to curb light pollution, reduce glare, and create a soothing — versus blinding — outdoor environment. Remember also that you don’t need many fixtures to make an impact outside; learn about my less-is-more approach to landscape lighting here.
As for dark sky-compliant fixtures, these picks will adequately illuminate your home and yard and facilitate stargazing.
Cover Photo: On Acadia National Park’s Schoodic Peninsula, Down East’s director of photography, Benjamin Williamson, captured the Milky Way and bioluminescence in the water.
Always start with the light bulb when deciding how you want to light a room or a wall or a piece of art or anything. The fixture is secondary to the lamp (how lights bulbs are referred to by lighting professionals). We are discussing directional lamps here so one of the most common lamp types is the MR16, a 2 inch diameter mirrored reflector. It is used extensively in recessed lights, track fixtures, monopoints and landscape lights. It is one of many directional lamps available today. Other directional lamps include PAR, BAR and AR. These designations are followed by numbers, 16, 20, 30, 38, etc. The numbers are the measurement of the face of the light bulb in 1/8th’s of inches. So a PAR38 is 4.75″ in diameter.
To determine which directional light source to use you need a basic understanding of photometrics, the measurement of the properties of light. Most fixture and light bulb manufacturers publish photometric tables that show how different lamps perform. These tables show footcandle levels at different distances from the light source and different aiming angles. They also show the distribution of light at different distances from the center beam of the light bulb. The center of the beam of a directional light is the brightest spot and the number of footcandles at that point is determined by Center Beam Candle Power, CBCP. Therefore you will see this terminology used when describing directional lamps. There is a lot or great information available in the UL app “LightSmart” that you can download for free at the app store.
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