[AZ-Observing] Re: Sky Brightness Change in Past 20 Years, The Real Motive
- From: Dan Heim <dan@xxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Fri, 17 Sep 2010 10:39:18 -0700
Indeed. Having all that excess generating capacity sit idle during
off-peak hours represents a loss to power companies. That was the whole
idea behind the new rate structures that encourage people to run their
dishwashers and other programmable appliances later in the evening. By
making off-peak electricity cheaper and changing consumers' power usage
habits, both parties win. But, as Richard points out, they're still
using the "light = safety" argument where it doesn't always apply.
That's where the latest generation of LED streetlights, now being tested
and already adopted by some municipalities, could have an impact. I have
seen these streetlights. APS is testing two models in a neighborhood in
north Phoenix. These are gen-2, and did not fare well, losing
significant brightness after only a year of operation, but the gen-3
lights are a significant improvement, both in longevity (= lower
maintenance costs) and efficiency (50% greater than gen-2 = lower
operating costs for the same illumination level).
But where they really "shine" is in their ability to be automatically
dimmed, say, after 1 pm when traffic drops significantly and safety
becomes a less valid argument. I read an article, in Scientific American
I believe, that pointed out how they could be equipped with sensors that
not only react to ambient light levels (as do current HPS street lights
for off/on) but also to the presence of a vehicle or pedestrian, to
temporarily ramp up the brightness as needed to accommodate late night
traffic. You can't dim an HPS, and they take too long to reach full
brightness to work like I just described. LEDs can do this easily.
This is why, in my presentations on light pollution, I say that DFAC
endorses the development and deployment of LED lighting. The lights use
blue LEDs with a special phosphor that down-converts the light to more
astronomy friendly colors. You still need enough "white" for accurate
color rendition, but much of the easily scattered shorter wavelengths
can be avoided. You can already buy a "warm" LED light for inside use
that more closely approximates the spectrum of an incandescent.
Dan Heim
President
Desert Foothills Astronomy Club
http://www.dfacaz.org
On 9/17/2010 9:40 AM, Richard Harshaw wrote:
> Given the fact that MOST of the power in this country is supplied by
> investor-owned utilities and that they make a lot of money off the lease of
> street lights and the sale of off-peak power for store lighting, etc., I
> don't think we'll make much progress on light pollution until we address the
> economic reality of power generation and distribution. Having worked for a
> public utility in a former life, I can vouch for the aggression they
> encourage in their engineers and sales reps to sell off-peak power and to
> "sell" the public on the idea that more night lighting makes for a safer
> community.
>
> Case in point-- when I lived in Kansas City, MO, a typical 400-watt HPS
> street light leased to the city for $450 a year. Multiply that by 100,000
> street lights and you can see why power companies promote night time lighting
> so heavily.
>
>
>
> Richard Harshaw
> Cave Creek, Arizona
> Brilliant Sky Observatory
>
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