14 August 2007
Are the stars out tonight?
I don't know if it's cloudy or bright, because so-called "light pollution" from millions of urban light sources make it difficult to see much of anything in the sky.
Streetlights make up around 38 percent of those sources, so any serious attempt to reduce light pollution must include streetlights. You don't want them too bright, for obvious reasons; you don't want them too dim, lest you provide opportunities for the sort of people who use darkness to cover their misdeeds. The Civil Twilight Collective proposes an elegantly-simple solution:
What if streetlights could respond to ambient moonlight, dimming and brightening each month as the moon cycles through its phases? On clear nights when the moon is full, streetlights might even turn off completely. The scheme, which they call "lunar-resonant streetlights," could save as much as 80-90 percent of the energy used in streetlighting while bringing back the experience of moonlight and stargazing to urban areas.
And come to think of it, the aforementioned evildoers don't really need darkness:
[I]ronically, studies have shown no link between outdoor lighting intensity and crime or accident rates. What's more dangerous, [Civil Twilight's Anton] Willis says, is the drastic variation in light levels within an urban area. As you drive, for example, from a well-lit major thoroughfare to a darkened residential street, your eye does not have time to adjust, and your vision is impaired. Moonlight is much more even, he explains, and that makes it more effective for human vision. By filling in only what light is needed, lunar-resonant streetlights would help restore this evenness and actually improve nighttime visibility.
And this evenly-lit utopia won't cost all that much, either:
Most of the necessary parts are available off the shelf. The standard cobra-head streetlights that we see on most American streets use a sodium-vapor bulb hooked to a photosensitive cell. The cell detects when the ambient light drops below a certain level (i.e. at sunset), and turns on the bulb. At sunrise the sensor perceives the increased light level and shuts the bulb off. The new sensor Civil Twilight has conceived would still respond to light levels but would be much more sensitive enough to respond to light from the moon. Because sodium bulbs are not dimmable, Civil Twilight's project would replace them with a cluster of white LEDs, which are also more efficient and require less maintenance.
The hard part, of course, will be selling it to cities and counties.
(Via AutoblogGreen.)Posted at 10:09 AM to Entirely Too Cool