The Davis Square Community

depending on if it's an input or output filters, we're talking "an inch circle" to a few inches, but probably not much more than a foot ;)

and they are expensive relatively speaking.

a window? probably not cost effective.

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I use a neodymium-based Baader Moon & Skyglow filter to cut out sodium lights. It's 1.25" in diameter, and cost around $50. That's probably not economical for a full window.

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Depending on how close to your house the light is, you may or may not be able to get the city to put up a shield/hood/whatever (don't know the proper term for it) so that the light isn't shining directly into your window. The purpose of the light is to illuminate the ground below it, not the inside of your house. I would try calling 311 and seeing if they're willing to do anything about it.

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dphilli1.livejournal.com

Except for the fact that I'm actually in Medford and I've already petitioned the city to have the light removed, including neighbor's signatures

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When I was in college, we used to "shoot out" lights by shining a laser pointer at the top of the light (you had to be above the light, pointing the laser downwards), so the light's photosensor thought it was day and shut off the light. I have no idea if that still works on today's lights, but a fixed laser pointer on a tripod in an attic window running on an AC adapter to shut off a street light would be pretty cool.

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clevernonsense.livejournal.com

At my old job, a residential neighbor used to "shoot out" the nearby flood light by...well, shooting it.

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you should lobby about having lights that only illuminate DOWN, and do not scatter light up.

that said, at the same power levels as street lights, i'm not seeing a "win" for LEDs. the sodiums as far as i know are simple, and burn forever.

LEDs require driver circuitry, and unless quite robust, are going to experience far more failures, and require replacement sooner. imho. they also run hot, and are power hungry. they might be dimmer, but will potentially provide a more sunlight like feel (good luck blocking that).

interesting to see what happens and their proposed studies on costs.

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sparr0.livejournal.com

LEDs at the same power as sodium lamps produce a light spectrum that provides for better night vision.

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ron_newman

Do LEDs really 'run hot'? I recall an early problem with LED traffic lights was that they did not generate enough heat (compared to the light bulbs they replaced) to melt ice on the outside of their lenses.

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Traffic lights have never used sodium vapor lights. Prior to using LEDs they used incandescent lights with filters. Look at http://en.wikipedia.org/wiki/Luminous_efficacy#Examples_2 for a chart with a listing of the relative efficiency/efficacy of various light sources (knowing that with incandescent traffic lights you throw away most of the light at the filter making them even less efficient) which you don't do with LEDs since the only emit light at a single wavelength (white LEDs have a phosphor coating on top of a blue LED which provides more wavelengths to provide white light).

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ringrose.livejournal.com

I'm not sure where your facts about sodium burning forever, while LEDs have failure, come from. Or that they run hot.

Google is your friend:
http://www.dmxledlights.com/OutdoorLighting/StreetLightsLU1/Comparison_HPS_vs_LED_Street_Lights.html
claims exactly the opposite. Of course, it's from a company which makes LED streetlights. So here's a report from a city in California evaluating replacing sodium with LEDs: http://sunnyvale.ca.gov/Portals/0/Sunnyvale/DPW/Transportation/LED%20Street%20Lighting%20Sunnyvale%203%2027%2012%20web.pdf

LEDs make equal visibility with lower power because they emit in a part of the spectrum for which our eyes are more sensitive. That's going to make filtering their light harder. However, the _direction_ they send the light is a lot more controlled than sodium.

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sorry, i was being ... mmm ... what's the word? enthusiastic in my terms. having talked with some electrical workers about them, and how they might maybe adjust a few to not shine in my yard, it came up that basically they were set and forget - they almost never had to replace them; when they did, they were modular to a point as well. just a bulb, or just a ballast, not whole integrated units. so working life could well exceed 5 years, much more even, which is forever in a sense.

i've had too many CFLs which have active [discrete?] circuitry simply fail in a month or three, most never lasting more than a year or two. range of failures from simple "just died" to "melting bases". not very shock sensitive or surge resistant is my best guess. hate them. i've converted to LED myself as fast as possible, and we'll see how that goes.

almost all of the direct screw in Edison style LEDs i've seen, the good ones anyway, that are very bright, have massive heat syncs, and some have fins, and what not. they're quite hot. perhaps not as hot as some light bulbs, but the myth they "run cool"... eh. even if they consume say 50-60% less power (which is a goodness), it's still quite a bit more than people realize. marketing?

that first link is "funny". all the praise and none of the potential downsides.

and good on Sunnyvale there, thanks for the link. I'll be reading all 100+ pages. good news for astronomers:

'''LEDs performed well in environmental and safety analysis. LED streetlights emitted far less light at high angles (80-90 degrees vertical) than high pressure sodium, reducing the potential for glare which is an important safety issue. LED products outperformed high pressure sodium in reducing light trespass with Vendor B having an edge. The city of Sunnyvale contributes to overall sky glow affecting the Lick Observatory as well as amateur stargazing – the more efficient LED distribution of light should reduce Sunnyvale’s contribution to overall sky glow. Finally, in contrast to LEDs, high pressure sodium lamps must be treated as universal waste due to mercury content.2'''

i've been a high power LED advocate for many many many years, but some of the magical myths about them annoy me. some of the flashlight i have (or have had), run quite hot - such that if you aren't personally heat syncing them, they will get hot enough to burn you; and they chew through batteries amazingly fast. that said, they're still the best thing i've seen thus far.

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starphire.livejournal.com

some notes in regard to your observations:
-both CFL and LED retrofit bulbs are in suboptimal packaging for a large percentage of all existing light fixtures in the world. Because an incandescent bulb is expected to generate mostly heat, fixtures were designed for appearance, nice light dispersion, and longevity using heat-resistant materials. Keeping the bulbs cool was not an important consideration for a century! But that's EXACTLY what you need for either a CFL or an LED bulb (because the ballast components are heat-sensitive, and failure rates for electronics generally follow the Arrhenius equation). With a CFL, the heat from the light-emitting part has a relatively large surface area, so it needs no metal heat sink, which adds cost and weight. But the CFL power supply (which also generates heat) has to be crammed into the base, as small and as cheap as possible to compete in stores with <$1 lightbulbs - because consumers tended to think of buying bulbs in terms of price at the register rather than in lifetime usage cost. That means billions of no-name bulbs dominating CFL sales, with rock-bottom component and construction quality, most installed in fixtures where heat is largely trapped around the bulb, where they fail long before their rated lifetime...or melt (as you note), or even catch on fire. Most CFLs have fine print saying "do not use in inverted (base up) position", precisely because the rising heat gets concentrated in the worst place. More costly CFL bulbs from brand-name manfacturers, in suitable fixtures, actually do live up to their claims - usually. Recessed ceiling fixtures are the worst...

-LED bulbs (the good ones you refer to) have those metal bodies to get heat away from the LED chips - because they produce heat in concentrated spots with little surface area and MUST have large heat sinks to keep those chips from frying. But they don't generate more heat than a CFL of equal wattage - it just feels that way to you, because aluminum conducts heat to your fingers so much better than glass or plastic! Their power consumption per lumen is FAR less than an incandescent, now better than CFLs too - and still getting better every year. There is no myth or marketing BS there, as you suggest - they consume what they say they do. US DOE expects the average LED bulb will be 120 lumens/Watt within 2 years, because LEDs coming out of the lab are already better than this.

-There are actually sound technical reasons why LED streetlights have better efficacy than sodium lights at getting light where it's wanted and not elsewhere, but no optical system is perfect in the real world. And as others noted, more light energy is matched to peak eye sensitivity. Interestingly, LED streetlights in colder climates have an advantage over ones in warmer cities, because the cooler the air temperature, the more efficient and long-lived the LEDs and drive electronics are! Also, electronic power supplies can have better Power Factor Correction than sodium ballasts, so better and more efficient for the electrical grid. Lots of small advantages that add up, so long as designs are robust and well-done and don't make silly compromises like trying to fit into a package that was designed for a different kind of technology. In that respect, LED streetlights are ALSO better off than LED retrofit light bulbs.

-Certain geek-magnet flashlights are designed with the aim of getting the most light out of the smallest package, which means those nice aluminum heat-conducting bodies get hot quickly and use up tiny batteries fast. That means nothing in terms of efficiency, it just means designers are making tradeoffs with certain performance priorities.

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LEDs actually run much cooler than most other lighting technologies, but they fail at much lower temperatures as well. Sodium lights do have circuitry in them that fail over time as do the bulbs. Look at http://en.wikipedia.org/wiki/Sodium-vapor_lamp#End_of_life to see their bulb failure state which is typically somewhere around 20,000 hours or about 4-5 years of operation. I have no idea how long the sodium lamp circuitry lasts but I do know that ballasts die over time.

LEDs themselves can last 5+ times this so you're more likely to be limited by the lifetime of any circuitry you build your lamps on. Most of the individual components can last almost indefinitely, it's typically any of the hundreds of connections that fail.

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much cooler in comparison is true, but they still run hot enough you can't hold or touch one after it's been on a bit - even flashlights. there's this myth that LEDs run oh so cool, like fluorescents might but even those guys get hot. makes sense though, pump in a lot of power, they get toasty. very few lightning technologies run cool.

as long as we're not getting bad components (capacitor rot), and they are surge protected (line power step down to LED power, regulation, they won't need some of the things flashlights do...), things should be golden for a long time. "should be".

CFLs have taught me to be very skeptical of line voltage powered drop in replacements for Edison bulbs. i'm glad they are going out of favor.

LEDs are the future thus far. they even lend themselves to light guides and lenses as well.

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As far as heat, it's really just a matter of efficiency and surface area. The higher the efficiency the less extra heat you create for the amount of light you produce. Until recently good fluorescent and good LED lighting were about equivalent (with different trade-offs) so they generated the same amount of waste heat. But since a fluorescent light has a larger surface area than a similar fixture of any other lighting type, there will be a lower temperature. LEDs are lower temperature than incandescents for the same output because they are more efficient.

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clevernonsense.livejournal.com

I'm curious where it says they run at the same power? My home town is in the process of switching slowly (as old ones break they get replaced) and the LED lights purportedly use less than half the energy and are simpler to replace if something goes wrong (simpler but more expensive). I'm sure there's a million options to choose from.

But yeah, "White LEDs" run on a rather broad spectrum unless particularly designed to be lower light pollution lamps (which I prefer, but they don't really light up dark street corners very well so maybe not a good idea for a city with a bit of street crime).

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http://users.livejournal.com/_meej_/

The City's electrical department would be able to tell you for sure, but the streetlights might be either Phillips Lumec's RoadStar series (the big cobra-head ones), or Sternberg Lighting's LED Libertyville series (the down-light vintage-style ones), or distantly possibly Phillips Lumec's Double Post Top LED series if they're the post-top pedestrian scale ones. I know they're all officially 4000K color temperature LED's, but given how much those temperatures change as the lights establish themselves it may be a futile cause with LEDs. Don't know much about emissions spectrums beyond that.

But I'd call 311 to ask about what the specific model in question is, and/or see if research can tell you if it's possible to tune out a 4000K color temp. LED light.

Good luck!

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Thanks! That's very helpful. Out of curiosity, how do you know those are the models being used?

If they are using LEDs to simulate a 4000K blackbody color temperature, that's good news. That's usually done with a combination of blue and red LEDs, which leaves a valley in the spectral response right around the Oxygen (III) bands, which happen to correspond to the color of certain nebulae. I don't have an O(III) band pass filter, but they are at least readily available.

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http://users.livejournal.com/_meej_/

I'm a landscape architect who's worked with the City on past projects; these were, as of a few years ago, the "standard" models the City let us know about at that time (public record, so I feel comfortable sharing them). No guarantee they're still current, but I haven't noticed a change in the overall look.

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starphire.livejournal.com

I don't know where you heard that a 4000K color temperature LED light is usually accomplished with a combination of blue and red LEDs, but as Xuth noted above most white LED lighting products actually use a blue LED in combination with one or more phosphors which convert much of the light into a broad spectrum of longer wavelengths, centered in the green and yellow part of the spectrum (or with a secondary peak in the orange-red if a warmer white color is desired).
LED streetlights are optimized for efficiency and visibility, which means cool or neutral white, not warm white. Here is a typical emission spectrum for a single-phosphor white LED excited by a blue LED:
http://en.wikipedia.org/wiki/File:White_LED.png
Formulations vary a bit between white LED manufacturers, but this is probably very similar to what Somerville's LED streetlights put out, whatever brand they use. They almost certainly do not use pure blue and red LEDs (which would be very magenta-looking and be a poor match for human eye sensitivity, which peaks in the green).

As you can see, there's a fair amount of light emitted at the sodium wavelength your filter blocks out, but most of the light is both longer and shorter wavelength and covers most of the visible spectrum. In other words, your filter would be fairly useless at blocking extraneous light from LED streetlights. And since such filters usually block a decent percentage of all other wavelengths as well, it'll probably do more harm than good to use it for looking at nebulae if the city switches over to LEDs completely.
The passband for an Oxygen(III) filter does happen to coincide nicely with an emission minimum around 500 nM.
Unfortunately, there is still a fair amount of light energy emitted even at 500 nM, because the overall spectrum emitted by these LEDs is so broad - unlike the sharp yellow peak emitted by sodium vapor streetlights. So again, you probably don't want to invest in one if you're trying to block light from LED streetlights.

I'd say your best hope is the fact that LED streetlights are typically much better at putting light on the ground rather than losing it out to the sides and upward, compared to sodium vapor lights. Hopefully that will reduce light pollution overall and improve your chances of seeing dim objects in the heavens, even without filters.

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