Author Topic: LEDs - Are they better?  (Read 264 times)

James Przystup

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LEDs - Are they better?
« on: December 27, 2017, 02:01:41 PM »
NYC's effort to replace all streetlights with bright white LEDs final reach my block a couple of weeks ago.

When my wife and I pulled up one night to find the new lights she actuallyfelt bad for me since the block looked like the parking lot of the local Stop and Shop.I was depressed about it for a bit but when I sat out in my backyard away from the direct light of the street. I wasn't sure if things were too different - perhaps no difference? The night sky above still looked dark. I'm not sure if it's wishful thinking but maybe the sky-glow from the old lights has reducedand thus improved while the immediate surroundings have brightened and thus degraded - making things even. I'm not sure - the jury is still out. I had a great observing session a couple of nights ago - actually seeing DSOs with better detail than I have before. I'm not sure if it's because the summer humidity was gone or whether the new lights were contributing.For now I'm just glad I was able to have a good night session after being immediately shocked at the difference.

Has anyone out there actually experienced improved viewing with the LED switch?



cardcudeflee

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Re: LEDs - Are they better?
« Reply #1 on: December 27, 2017, 07:44:45 PM »
When I'm on a commercial flight, I notice a big difference flying over neighbourhoods with LED street lighting. There is way less light trespass to the sky above. All I typically see is a dim glow on the pavement, with no sense of where the light originates. Old-school sodium fixtures are WAY worse - at least when seen from the air.

Kapil Majmudar

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Re: LEDs - Are they better?
« Reply #2 on: December 30, 2017, 09:31:37 AM »
Quote
When I'm on a commercial flight, I notice a big difference flying over neighbourhoods with LED street lighting. There is way less light trespass to the sky above. All I typically see is a dim glow on the pavement, with no sense of where the light originates. Old-school sodium fixtures are WAY worse - at least when seen from the air.


I think the primary difference you are seeing is that the new LED lights tend to emit directly downard and are usually also hooded (which blocks direct upward emission, which is just wasteful anyway), whereas the more common sodium vapor lamps are often not. Here in Colorado, it is not uncommon to see high pressure sodium vapor lamps without any kind of hooding, which is both wasteful (emits light outward and upward, when it only needs to be directed downward).

I am not so sure about LED as a replacement. I did some research a while back. The basic low pressure sodium vapor lamp is probably the most AP-friendly light source, especially when the lamp is properly hooded. They emit in a very few narrow bands, which existing LP filters already block out (and with the likes of the IDAS LPS-P2 or -D1, block out without blocking a broad spectrum). Another benefit of low pressure sodium lamps is they are actually pretty efficient. They have very long lifetimes, up to 80,000 hours. They are very cheap to manufacture, and don't require the wide variety of more volatile and toxic manufacturing procedures that the highly electronic LED lamps do. Whenever I head out to my dark sites, I see low pressure sodium and low pressure mercury lamps around. They can light a small area, but in general they are really quite dim compared to your average city lighting. It's quite nice, IMO. I kind of think we USED to have broad distribution of the best AP-friendly lamps available, and wish we could go back.

High pressure sodium vapor lamps are worse. The emit more bands, brighter bands, and sometimes are mixed with mercury vapor as well, which increases the breadth of spectrum even further. Many of those bands can be and are filtered out by LP filters, but they are used because they are a lot brighter, and obviously that pumps more photons into the sky. Hooding these street lights certainly helps, but they can still bounce a lot of excess light off the ground.

The thing about LED lamps that I worry about is the fact that, while their spectrum is a little spiky, they have a pretty decent broadband emission across the visible spectrum. Hooding them is good, and if they are lower power, they will be dimmer, and that is also good. However as cities continue to expand (at scary rates, Denver is expanding at an accelerating rate and our bortle scale LP map went from a tiny white spot right around downtown Denver itself to that white zone nearly reaching me miles and miles away in less than three years), the sheer volume of city lights will result in further increases to LP, and eventually it will be less filterable LP. The problem with LED light is it's broad spectrum...so LP filters will loose effectiveness or be minimally effective.

I am honestly not sure if high pressure sodium or LED is worse in the long run. LED is costly to move to, and if I had any decision making power, I'd push to move back to lower energy, dimmer low-pressure sodium vapor lamps and ensure that all city lighting was hooded.

unetankem

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Re: LEDs - Are they better?
« Reply #3 on: December 30, 2017, 10:07:31 PM »
Something to keep in mind is that light at wavelengths less than 500 nm is subject to Rayleigh scatter off of air molecules, which contributes to sky glow. Granted, LED lamp fixtures with better shielding certainly will reduce light trespass over high pressure sodium lamps. However, light scatter at wavelengths less than 500 nm will be independent of the fixture design, since the light will scatter off of the air molecules into random directions as soon as that light leaves the lamp source.

It is possible to conceive of an LED lamp and a high pressure lamp with the same spectral content at wavelengths less than 500 nm. One would think that they would equally contribute to sky glow in this respect. The lower the color temperature, the less light that will be emitted at wavelengths less than 500 nm. This is why LEDs of 3000 K color temp, and less, are preferred. I have had success getting my town to consider LEDs closer to 3000 K, whereas they had been contemplating lamps in the 3400 K to 4000 K range, previously.

The one advantage that LEDs have over high pressure sodium lamps is that this blue component can be filtered out very effectively. Such units are being installed in Hilo, HI:

http://cwenergyusa.com/star-friendly/

The added filtering means that each such lamp is about $300 more expensive than a lamp without filtering. So it is a bit of a hard sell to communities with only so much grant money for the switch-over to LEDs.

Even if such blue-filtering is put in place, there is the remaining, continuous spectrum at wavelengths longer than 500nm which will scatter off of the ground, as Jon mentions above. I am thus "enjoying" the high pressure sodium lamps for as long as possible.

Regards,

Gary

esicnatka

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Re: LEDs - Are they better?
« Reply #4 on: December 31, 2017, 05:49:44 PM »
Quote
However, light scatter at wavelengths less than 500 nm will be independent of the fixture design, since the light will scatter off of the air molecules into random directions as soon as that light leaves the lamp source.


I am guessing there is not too much light scatter between the 25 feet or so height of the fixture the fixture and the ground, at least insignificant compared to the light thrown up into the air by a HPS cobra head fixture.

Antonio Zuniga

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Re: LEDs - Are they better?
« Reply #5 on: January 01, 2018, 02:39:45 AM »
I think the key question to ask is, "What kind of LED's?" There are lots of them. If we put up only red ones, I'd be okay with that, but then, that wouldn't light streets or sidewalks very well.

Most LED's on the market right now are high intensity LED's, that have a lot of blue in them. I've seen some that look almost purple - and those ones wereso bright, they actually hurt my eyes while walking under them. LED's can be "tuned" to different color temperatures - typically some phosphorus is put on the part that glows to help diminish the blue and soften the color to have a bit more red. However, they still put out more blue light than most others.

Ideally, we'd want lights that areonly bright enough to do the job, and unfortunately, we really don't have lighting standards (in the U.S. anyway) that do that. We just have some vague guidelines that largely say, "Well, sure you can see a person's face from X feet away at Y number of footcandles" or some such. But what we really need is some minimums and maximums... but those don't really exist, because no one has asked, "SHOULD we be using this much light at night?" (a question well worth asking, I might add, given the implications for sleep, at minimum, never mind the rest of the natural environment that doesn't have the option to pull the shades down).

But I digress....

Are LED's better? Depends. Which LED's? That's the main question. We should also ask: How much light do they produce? How much light is present where it is needed, and how much is going outside that target area?What is the spectrum of the light they produce? Once we know those answers, then we know whether they are better, or worse.

But those questions are rarely asked.

If the light is aimed to only light downward, aimed / shielded from going outside the target area, only produces enough light to illuminate the target area for the minimum necessary, and produces little blue or violet light with no direct line-of-sight to the fixture so at to avoid glare - then yes, it's probably a good LED. But then, that applies toany light fixture too.

Nong Inthisorn

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Re: LEDs - Are they better?
« Reply #6 on: January 08, 2018, 08:41:28 PM »
"
The problem with LED light is it's broad spectrum...so LP filters will loose effectiveness or be minimally effective.
"

The new Target parking lot ~1mile crow-fly away sure proves that here.
On a bad night, I'm back to using old haze and sky filters.

On the plus side, a good night is still pretty good, because most new LED
 assemblies have a less dispersed beam than old arc lights. It's an extra
efficiency: more posts, lower consumption.

"Warm" LED floodlights still have a fair amount of the violet stimulus to them.
That's easy to filter out, but I'm not sure any maker does.

bamrocorna

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Re: LEDs - Are they better?
« Reply #7 on: January 09, 2018, 08:15:11 PM »
Quote
"Warm" LED floodlights still have a fair amount of the violet stimulus to them.
That's easy to filter out, but I'm not sure any maker does.

There is one U.S. manufacturer who is producing blue-filtered LEDs, C&W Energy Solutions. The city
of Hilo, HI has been converting from low pressure sodium to these units:

http://cwenergyusa.com/star-friendly/

In fact, I have a couple samples of their filtered LED units here in my house (just the lights with filters, but not
the shielded enclosures). I have been using them for demonstration purposes to try to educate the public.

~Gary

John Fimbres

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Re: LEDs - Are they better?
« Reply #8 on: January 12, 2018, 07:10:44 PM »
Quote
........

Ideally, we'd want lights that areonly bright enough to do the job, and unfortunately, we really don't have lighting standards (in the U.S. anyway) that do that. We just have some vague guidelines that largely say, "Well, sure you can see a person's face from X feet away at Y number of footcandles" or some such. But what we really need is some minimums and maximums... but those don't really exist, because no one has asked,......

Actually, the recently passed LP Law in New York State requires a state agency ( I forget which one ) to develop street lighting standards that must proscribe the minimum light level for driving and walking safety. There is a "required by" date for the standards (think it's a year), and after that all State paid-for street lighting must comply with the standard, unless there is some extra exemption, like maybe a firehouse.

The Assemblywoman who introduced the bill that became this law is now working on a new one that, if passed, will pass the requirements to meet the standards down to local gov and large commercial entities. Her new bill will also address LED streetlight color.

pernogori

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Re: LEDs - Are they better?
« Reply #9 on: January 13, 2018, 05:13:59 AM »
Quote
........

Are LED's better? Depends. Which LED's? That's the main question. We should also ask: How much light do they produce? How much light is present where it is needed, and how much is going outside that target area?What is the spectrum of the light they produce? Once we know those answers, then we know whether they are better, or worse........

Note that just about all LED streetlights (and parking lot lights) are full-cutoff by design. ( Not to mention that now NYS, and several of the New England states have laws that require full-cutoff ).

As discussed in a local town board meeting near where I live: the brightness of LED streetlights is easily adjustable - so if laws or public pressure demand dimmer, it is easy to do without any physical change. This fact came out (from the manufacturer)in response to one town board member's question "What do we do if people complain that they are too bright?"

The latest issue of Nat Geo notes (again) the increasing popularity of "smart" streetlight systems, that adjust brightness depending on weather and traffic, all controlled by a central computer - that can be re-programed to adjust brightness and timing.

The one thing that is costly and difficult to change with LED streetlights - their color.

Micheal Luther

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Re: LEDs - Are they better?
« Reply #10 on: January 13, 2018, 06:58:36 AM »
I've noticed that some of the dreaded mercury-vapor and HPS NEMA-head "security" lights in my area are being swapped out for the LED version. It's not perfect, but it's MUCH better in terms of glare and skyglow. I've actually been able to see stars directly above these kinds of lights, as the newer LED's lack the veiling, harsh glare of the MV/HPS versions.

The LED streetlights that replace the drop-lens HPS "cobrahead" fixtures are also far, far better.

The horizontally-scattered light is especially destructive for stargazing, so the fact these newer LED fixtures cut off illumination above 90° is something that could be of great benefit.
The one that worries me is the "decorative" streetlights along main street in many small towns. There are several companies that make "corn cob" LED bulbs that replace mercury vapor or HPS. If the *bulb* is replaced, but not the *fixture*, these could be *dramatically* worse sources of light pollution if the wattage is matched instead of the lumens.

It all boils down to fixture selection and their orientation.

Clear Skies,
Phil

Ivan Deane

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Re: LEDs - Are they better?
« Reply #11 on: January 13, 2018, 03:58:35 PM »
Quote
Quote

........

Are LED's better? Depends. Which LED's? That's the main question. We should also ask: How much light do they produce? How much light is present where it is needed, and how much is going outside that target area?What is the spectrum of the light they produce? Once we know those answers, then we know whether they are better, or worse........

Note that just about all LED streetlights (and parking lot lights) are full-cutoff by design.

...assuming they are installed correctly (which, as we see with many poorly installed "older" type of lights, does not always happen). There is a Catholic Church 1/4 mile from my house, which used to have high pressure sodium lights angled at about 70 degrees. I thought it was strange one night driving home that I could see these very bright white lights in that direction, which used to have this bright orange glow there. Then I realized: They replaced the high pressure sodium with LED's... at the SAME ridiculously bad angle.

By the way, the high pressure sodium ones they'd had before would have been "full cut off".... if they'd been installed correctly too.

We have a long way to go to educate people about how to light things properly, even with LED's.

Tye Paez

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Re: LEDs - Are they better?
« Reply #12 on: January 13, 2018, 09:23:49 PM »
Quote
I've noticed that some of the dreaded mercury-vapor and HPS NEMA-head "security" lights in my area are being swapped out for the LED version. It's not perfect, but it's MUCH better in terms of glare and skyglow. I've actually been able to see stars directly above these kinds of lights, as the newer LED's lack the veiling, harsh glare of the MV/HPS versions.

The LED streetlights that replace the drop-lens HPS "cobrahead" fixtures are also far, far better.

The horizontally-scattered light is especially destructive for stargazing, so the fact these newer LED fixtures cut off illumination above 90° is something that could be of great benefit.
The one that worries me is the "decorative" streetlights along main street in many small towns. There are several companies that make "corn cob" LED bulbs that replace mercury vapor or HPS. If the *bulb* is replaced, but not the *fixture*, these could be *dramatically* worse sources of light pollution if the wattage is matched instead of the lumens.

It all boils down to fixture selection and their orientation.

Clear Skies,
Phil

Are the "decorative" streetlights look like these? That's what I have in my neighborhood. They light up everything in all directions. I would love to find a solution for these other then painting one side as one guy did to block the light from entering his bedroom

Attached Thumbnails


Noe Subeydhi

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Re: LEDs - Are they better?
« Reply #13 on: January 15, 2018, 02:48:01 PM »
Yes, this is one of the worst light polluting fixtures out there. Half the output spills uselessly horizontal or upwards. It'd be nice if the folks who dream up these "streetscape" projects with "vintage"/"historical" lighting would ponder if those streets were historically lit with the crazy intensity of today's glare bombs.

There are lots of "decorative" street light fixtures out there with LED's, and quite a few of them are actually cutoff designs.

Clear Skies,
Phil

ropnolini

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Re: LEDs - Are they better?
« Reply #14 on: January 18, 2018, 03:38:49 AM »
Quote
Yes, this is one of the worst light polluting fixtures out there. Half the output spills uselessly horizontal or upwards. It'd be nice if the folks who dream up these "streetscape" projects with "vintage"/"historical" lighting would ponder if those streets were historically lit with the crazy intensity of today's glare bombs.

There are lots of "decorative" street light fixtures out there with LED's, and quite a few of them are actually cutoff designs.

Clear Skies,
Phil

Phill, thanks for your feedback. I thought they where the worse too. Sure would like to find a bulb that had a cutoff topping that could be switched out easily.

Anyone out there know where you could buy some?