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Profile, Quizzical

A delightful urban design idea

Streetlights that shut down when the moon is full. They even save energy.

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It's a nice thought, but...

Given that moonlight doesn't have nearly the strength of sunlight, I'd imagine the dark corners illuminated by either direct streetlights or reflected sunlight would, at night, remain awfully dark. In a city the size & type of San Francisco this would provide some awesome cover for all manner of criminal activity (victimless and otherwise). It might work in a city the size of Ashland or Eugene, but no larger.

Moonlight is what, around 5/100 of a footcandle? I'd be willing to bet that the light given by the streetlights is such that the moon isn't even a close replacement. Admittedly, the same might be said about sunlight vs. an auto-dimmed fluorescent system in an office, but the difference there is that the lesser source of light is the controlled, directed one. It's telling that the most interesting image on the page is a "photo simulation," likely because the image is visually impossible. Again, for the light levels you see in the sky there'd be next to no apparent illumination on the ground. (Sort of like in a movie set in space, where you can't see stars if the earth is visible but they always show them.)

Maybe I'm too natural a skeptic, but I don't see that working well at all. Sort of like cooling a busy pizza kitchen with unassisted natural ventilation. It's annoying, but sometimes you really need a fan. It may well be that they are right & we don't need nearly as much light as we have, but given the lunar geometry I doubt this is the solution.

Their web site actually has numbers; on a full moon night, it's about 1/10 of a footcandle. That's not so bad. I think it's at least worth a try. And streetlights make shadows darker by contrast and may actually make matters worse; there would be sky glow on moonlit nights.

One trouble there is (as I see it anyway) that the city they use as exemplar, San Francisco, has a big lunar geometry problem. 1/10 of a footcandle's fine in a field. On a city block with buildings 30' to 200' tall blocking direct visual access to the moon it's woefully inadequate, especially if you don't require everyone in the city to turn off their lights at night. Doing so might allow for eyes to adjust to the light levels where the light can actually penetrate. Failing to do so ensures night blindness. (And I'm skeptical that nighttime sky glow will provide much more than token illumination. Given that the open night sky isn't sufficient to, by contrast, obscure the light coming from a magnitude +6 star I find it stretching credulity to imagine it lighting an alley in Old Town. Please correct me if I'm wrong, but given that the sun produces about 50,000 footcandles, if we look at the moon at 1/10 a footcandle, and assuming the ratios remain relatively accurate, we have illumination levels below 1/100th of a footcandle. That seems less than effective for much beyond mugging.)

Having navigated many campsites (and after hours ren faires) via moonlight and sky glow, I have to say it's sketchy even when the only menaces are tree roots and drunken scotsmen. Even a fire can cause temporary blindness, and were I to catch headlights (especially the new, blue-skewed ones) I'd be blind as a bat for several seconds. As well, the human eye was adapted to slow changes, both in lighting conditions and in geography. Even with headlights, driving through a city at night at 30MPH would take on a new and exiting level of pedestrian danger, not to mention driver confusion as to location. Furthermore it works marginally well for people with good night sight, but it could be crippling for anyone with less light sensitivity. People who now function marginally with the overly bright streetlights would be utterly removed from life after sunset.

Again, it's a nice idea. But until one can turn every light source down it's extremely problematic, and even then it's serving only a portion of the population and potentially disserving some not so put upon by the current system.

I expect you are right. It would be interesting to design a city around the idea, though; it might even be useful. Besides, I think an inside-out simulation where the windows are an exterior light source would be cool.

It would. I agree with you on the windows idea. If indeed the standard for exterior urban lighting was set to burn off excess power then we need to think of ways to limit it. Perhaps a system whereby buildings were fitted with LEDs, both filling in what light gaps occur due to the current HID systems (which, I suspect, already greatly reduce power over what I assume to be original incandescent levels) and giving clearer definition to landmarks at night, and maybe have the added benefit of diffusing the light so less of it returns as sky glow.

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