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    Re: LED Street Lights
    From: Frank Reed
    Date: 2017 Aug 26, 13:13 -0700

    David, you wrote:
    "I have read that LEDs increases light pollution."

    Not by their nature, but by the economics that accompany the transition, yes, they do.

    LEDs, especially when subsidized, are cheaper than other lights at the same brightness level by, let's say, a factor of two, and they also last longer by at least a factor of five. In addition, they consume far less electric energy (again, let's say by a factor of five) and thus have a correponding lower environmental footprint. Overall, they cost radically less. Unfortunately, rather than passing along the full benefits of these savings to taxpayers and others paying the bills, governments and other decision-makers are sold a false benefit: "since the cost to you is reduced by 90% [or some other number], why not buy twice as much illumination? You'll double the brightness and double the safety [so goes the argument] and still pass along an 80% reduction in net costs to your taxpayers! Well, of course, we'll make that 70% since you and I both need a raise for making all this efficiency happen, don't we?" This false logic applies just as easily in homes and backyards and storefronts and most especially on government properties. Anywhere you can save money on lighting by installing LED lighting, the savings are split: half goes into direct savings and half goes into buying much more illumination. 

    In short, the LED revolution is rapidly increasing light pollution almost everywhere. The little astronomical organizations that have been fighting against light pollution via the bait-and-switch of reduced cost and reduced environmental impact have been blown away. LED technology delivered what they promised and provided brighter outdoor lighting, too. They should have been direct and honest about saving the night sky. Now it's too late. The battle has been lost.

    I have some hope that other technology can help, especially timed and motion-activated lighting. Businesses don't need their storefront lighting on at 3:00 in the morning, homeowners don't need their trees illuminated (!!) at 3:00 in the morning, and security lighting is not effective if it is always on. The night sky before midnight is probably a lost cause, but there's some chance we could actually get nice dark skies again in the wee hours of the night. And if we could convince our neighbors (and governments) to focus on the two weeks around New Moon and admit that we have little reason to worry about artificial lighting around Full Moon, well then maybe the trend can be reversed on those days when it counts.

    Here on Conanicut Island, I check the zenithal limiting magnitude now and then. It has risen in the past five years, but there's a noticeable improvement late at night. In the early part of the night, 90 minutes after sunset, the limiting magnitude is around 4.5, even 4.0 when there's snow on the ground. After 1:00 in the morning, the limiting magnitude is about 5.5. By then the sky looks quite nice. I won't say impressive since that's a full magnitude deeper and every step of one magnitude approximately triples the number of stars that are visible, but it's nice! We can see the Milky Way here on any clear moonless night, and late at night there are something like 2500 stars visible without optical aid.

    Frank Reed

       
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