We tend to romanticize the glow that emanates from city lights. We don’t often realize that any light that goes into the sky represents wasted energy, about $2.2 billion per year according to one popular estimate. Not only does light pollution run up electric bills and create carbon emissions, it interferes with ecosystems and obscures our view of the heavens. Of the roughly 7,000 stars that are bright enough to be detected by the human eye in each hemisphere, only about 800 of them are visible with moderate light pollution conditions found in the suburbs and 25 are visible in the heart of the largest cities. This is a problem we have brought on ourselves. We should ask: do we need to see that parking lot from outer space?
Fortunately, lighting technology can solve many of these problems. We asked GE’s outdoor lighting guru Tim Miller about how smarter lighting can bring back the night sky. His solution: LEDs. Light emitting diodes use about 70 percent less energy than the most common outdoor lighting technologies. They also reduce four components of light pollution: high light levels, uplight, trespass light and glare. LEDs can…
1. Decrease lighting levels
“Most applications are way overlit,” says Miller. There are two causes of overlighting. First, retailers want their parking lots to be the brightest. Second, it’s hard to achieve lighting uniformity. Uniformity is the even glow a full moon casts on all objects on a cloudless night. In many parking lots, Miller says, it can be bright as day under a light post “but if you drive off in a corner, it’s very dim.” With high-intensity discharge (HID) lamps, the lighting technology commonly used in parking lots, the uniformity ratio is 10 or 20 to 1 from the brightest spot to the dimmest. With LEDs, the ratio of the brightest spot to the dimmest spot is about 2 to 1. Better uniformity means less light is needed to illuminate an area.
2. Bring uplight down
Large parking lots are often visible from miles away because so much of their light goes up into the sky rather than focusing on the asphalt below. This is called uplight, and it’s often the result of the reflectors in HID lamps. LEDs don’t have this problem because, unlike incandescent and flurorescent sources, they don’t require reflectors to focus in one direction.
3. Arrest trespass light
Trespass light is unwanted light that enters another property. Trespass light is, by definition, wasted energy and it annoys neighbors. Many municipalities have ordinances limiting the brightness off of the property. LEED, a sustainable building standard, awards points for limiting trespass light and skyglow. Directional lights like LEDs are the remedy.
4. Limit glare
People tend to experience glare differently so there isn’t one good measure for it. But Miller defines it thus: You’re driving down a dark highway and you see a big box store. “It distracts your eye from focusing on the highway,” says Miller. Glare is exacerbated when there is a single light source, such as an arc gap in HID lighting. LEDs have the advantage of having multiple sources of light.
Article by Matthew Van Dusen, appearing courtesy Txchnologist.
photo: Joe Gray
