low pressure sodium lights

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LEDs dimming with long term use

I too have noticed LEDs dim some over very long usage-discovered this with a GE green LED alarm clock I got new in 1980;when I first got the clock it would light up a dark room and the transformer area would get warm when brightness turned all the way up-after a few years,display had dimmed noticeably and transformer no longer would get warm at full brightness-indicating the aged LEDs were pulling less current than they did when new-interesting...The clock is still in use and no further dimming has been noticed for the last ~30 years.I have an outdoor LED that has been on over 3 years and I might compare that one to an unused same type one bought at same time to see if any dimming noticed.With the low pressure sodium fixture,the color changes over long warmup process is kinda cool to watch-mostly red/orange with a little purple,then the yellow starts to appear as lamp warms.
 
I just sorta hope the LED chip assembly and the LED driver boards are replaceable in the LED outdoor parking lot and street lights-otherwise these can get expensive--hate to have to replace the whole fixture!Then the LED fixtures wouldn't be so cost effective.At least with HID lights you can easily replace the bulb or ballast.-Often with the fixture still in place.I have seen a LED wallpack light in LOWES-the lamp is on their display of outdoor lights-this was installed a month ago-it was very bright at first-and a nice white "4K" light.Now its dim and barely lights.So much for that light-will buy the MH fixture next to the LED one instead-the 100W MH bulb will generate more light-and last much longer-up to 3-5 years.I like to watch HID lamp warmups,too esp the HP and LP sodiums-My LP lamp fixture and bulb is still packed somewhere from a move-will have to look for it and fire the thing up-time for some ghostly yellow light!Its a wallpack light and uses a 35 or 55W bulb can't remember just which-haven't used it for sometime.
 
These are our new, standard street lamp/post design...

 

 

<span style="font-size: medium;">They have started to replace all of the old (55+ years) cobra heads in NYC. We're making the jump from HPS to LEDS. We're getting over 250,000 of these. Changeover should be complete by 2017. </span>

 



 



 



 



 



 



 
 
Great design, but...

if it is true that induction lighting is superior to LED in efficiency and durability, NYC is wasting money installing a superceded lighting system - but it looks good.
 
Low pressure sodium lamps are a superior technology used all over Europe but they never caught on in the US. Probably for 3 major reasons.

 

1. they produce a monochromatic yellow and have a color rendering index of zero. So color under them is impossible to distinguish.

 

2. they only last about 18,000 hours, still long, but nothing compared to the Mercury Vapor lamps from the 50s and 60s that were built to last 24,000+ hours, and most easily took the plus in consideration with some running over 100,000 hours. Yes at that point they would get very dim, but they lasted with few failures. HPS goes for about 24,000 hours with some newer non cycling lamps doing 30,000+. Energy was cheap back then, so life was about the only concern.

 

3. LPS lamps have a very, very long arc tube. The 180 watt version which is the highest available in the US and is equivalent to about a 250 to 400 HPS produces good light for lighting high ways, however the bulb is about 4 feet long and thicker than a beer can. The results are large long fixtures that do very poorly in the wind. The extra wind load means more metal for the fixture, more robust arm along with a thicker pole. Nothing like the cobra heads we are used to.

 

However, I think they would have done well for lighting small streets in the 18 and 35 watt versions, but its one of those technologies that should have caught on but didn't.

 

Either way where I live both LED and induction are replacing everything be it incandescent, Mercury vapor, HPS, metal halide and linear fluorescents that were dominant in gas station canopies and signs.
 
Those new fixtures being installed in NYC appear to be pretty nice-how about a picture of one operating when its completly dark-than could get an idea how these lights work and look.
The lower wattage LP sodium lamps were among those introduced into the US in the 70'sI did see the higher wattage LP lights at of all places a Scotties lumber and home improvement place in Ft Walten Beach,Fla.When I first saw them-so weird.And yes,LP bulbs-the larger ones are a lineal light source like a flourescent bulb-long-these cannot be focused as easily as the short arc bulbs of the HID family,and the fixures as stated-are bulkier and heavier.And to make matters worse--more expensive.
The real durability of the LED streetlamps and induction lamps still has to be seen-they are new technologies for this purpose.Induction lights are also being sold as real high dollar plant grow lights from plant grow supply catalogs-same with LED grow lamps.The HID ones-HP sodium and metal halide-are least expensive-both of these are getting efficiency boosts--from digital electronic ballasts.Other advantages of the digital ballasts over the magnetic ones-you can operate HP sodium and metal halide bulbs of the same wattage or as marked on the ballast case.And some of these have dimming capabilities-difficult with magnetic ballasts.
We just hope in the new LED streetlamps being installed-like what I said in the other thread-the LED light modules and control boards are easily replaceable.Otherwise the LED fixtures will be VERY expensive to maintain.At least with HID light fixtures the bulbs and ballasts are easy to replace.Since these are well known and established bulbs and ballasts are avalaible from many suppliers.The LED fixed lighting infanstructure is still very young-in "baby pants".
Oh yes another advantage of the LP sodium bulbs-they have instant restrike ablities in case of momentary power interruption-they can relight instantly without waiting for cooldown.-and relight at full brightness.
 
I remember when the city of Berkeley went over to LPS for lighting on its main avenues - Telegraph, Shattuck, University - back in the 1970's. At the time I also remember angry letters to the editor lambasting the lighting as a tool of the fascist police state. Supposedly because they didn't cast any shadows for a protestor to hide in.

In any case, they did cast an ugly light. I think the city has long since gone over to HPS, and is probably thinking LED's at this point, if not already converted.

In my current town, a nearby street signal went to LED's about five years back. Apparently the technology they used wasn't quite up to snuff, because within a year the signals had burnt out LED's. Other ones installed later seem to be doing better.
 
Same in NYC...

 

 

<span style="font-size: medium;">Traffic and pedestrian signals were converted to LED's about nine years ago. Within a month, I  noticed individual LED's burning out. It's very rare to see ANY signal here without a least 2 or 3 LED's out. </span>
 
LED traffic signal

one complaint I have heard with LED traffic lights is they won't melt off snow accumulation like the incandescent ones-same thing with LED lights on truck trailers.
 
Here in the twin cities of St. Paul/Mpls. LED traffic signals have been a mixed bag. What I have noticed more than anything is that many municipalities are using LEDs for the RED signal but sticking to long-life incandescents for the green and amber. I wonder if the reliability of the the LED as a red combined with the heat producing qualities of the green and amber are a win-win in a snow and ice laden environment!
 
 

 

<span style="font-size: medium;">Most of the suspension bridges "necklace" lights here have been converted to LED's. They are noticeably dimmer than the old mercury vapor lamps.</span>

 

<span style="font-size: medium;">As for snow and ice accumulating on traffic signals, I don't recall ever seeing that here.
</span>
 
Traffic Signals

The quick failure of traffic signals gives me reason to be concerned about the life expectancy of LED street lamps.

 

Several years ago when post-deregulation delivery of electrical power fell short of needs and we experienced black-outs, brown-outs and costs for electricity soared all over the state, cities quickly went to total LED traffic signals.  Many signals had already been changed to LED for the red only,  but suddenly the green ones were changed out in nearly every city in the bay region, and some of them were failing within weeks. 

 

What I find interesting is that the red LEDs don't seem to have anywhere near the failure rate of the green ones.  I don't know what the implications are for clear lights, if any.

 

On the vast majority of signals in Bay Area communities the amber remains incandescent, likely because changing to LED wouldn't be so immediately cost effective as with red and green.
 
I haven't seen a NEW traffic light installed anywhere in MN in the past 10 years that isn't fully LED. Initially there was a trend to retrofit only the red portion of the existing lights. I'm not sure if it was because red LED's tend to be the cheapest to make or because liability is more of an issue if the red lamp doesn't work, I suspect the latter.

Of course with any new technology, as LED retrofits for traffic signals was years ago, there is the possibility of failures. I have seen a few lights that have an LED or two dark on the array. A few years ago I saw some of the red LED arrays for traffic lights at AxMan surplus. The array was built out of leaded low power indicator LED's. My hunch is that today they are made with surface mount power style LED's which would be much more reliable.

Bear in mind that the white LED's we are using for lighting are actually ultraviolet emitters that are exciting a phosphor to create the broad band white light. Yes they have difficulty with "Lumen maintenance" (loss of light output over time), but unless their safe operating temperature is exceeded, they will maintain brightness as well or better then any other form of light I can think of.

As for snow or icing being a hazard to LED lamps, they would actually work better frozen in a block of ice! No thermal issues that way and the junction voltage is so low that water would cause no harm. Other then high temps the only other things that could shorten an LED's lifespan are surges and these can be easily controlled with a TVS avalanche diode or MOV. Compared to an incandescent lamp any properly designed LED will outlast it by any order of magnitude at the least.
 
Phosphors in white LED lights-think the phosphors break down in time-this happens with flourescent bulbs and mercury and metal halide bulbs that have phosphors in them.The brightness and "color" of the light changes and dims.Otherwise the light still works.Stores lit with MH bulbs in open fixtures love the phosphored MH bulbs-they don't have glare and give a softer,more even light.Thats a good point for LEDS-they don't mind cold conditions that other light sources don't like-the extreme cold may not permit the light to start-flourescents,Mercury and probe start metal halide.Pulse start metal halides are more tolerent of cold-they can start more easily.But--Hids don't like extreme heat.Same with flourescent-MH bulbs are more tolerent of heat.Only danger is will the ballast get too hot-and fail.In a well designed fixture-the ballast is below the optical-so the heat from the bulb won't cook the ballast and its capacitor or ignitor.With light technology going the way it is-incandescent light fans are going to have to STOCK UP and buy as many CASES of bulbs they can.
I have also seen the LED traffic lights at surplus sales,too-these typically have MANY of the LEDS burned out.Yes,think fixture makers are going to the "chip" type LEDS as opposed to the individual "pilot light" ones.I have a flashlight that is multicolor 4 LED types in it-UV,Blue,Red,Green.The Powertac Chameleon.With some of its switch combinations you can mix the colors.You can see the phosphors of white LEDs by shining a UV lamp into them.
 
I dunno about stocking up on incandescents...

I overreacted a couple of years ago and ended up with about 12-14 4-packs of 100 watt bulbs. (There are different varieties, such as GE Reveal and Sylvania Daylight, as well as regular yellow bulbs.) Yet, I currently only am using 100 watt bulbs in a grand total of ONE lamp. Assuming they last a year, I'm well fixed unless I live to be over 100. Sheesh.

On the bright side, they weren't expensive, so no great loss even if they end up being tossed.

I bought one of the Cree LEDs for a stairwell light that is on a lot. It's a big improvement over CFLs, which are slow to light up, and the energy consumption makes it a better choice for this location than an incandescent. Still, the light is on the bluish side and I wouldn't like that everywhere in the house.
 
I just read that as of January 2014 they are no longer going to make 60watt and 40 watt regular bulbs. all are going to be one of the 3 new forms of lighting. They still will make higher wattages for special lighting. So now do we want to stock up on a few of these before there gone?
 
John (Supersuds), I'm glad you bought one of the Cree LED replacement lamps, they are the most incandescent like and most cost effective lamp available today. Nice that they are made here in the US too.

It sounds like you got the "Daylight" version which is a 5000K color temp and will have a bluish white light. All the Cree lamps I have are 2700K "Soft White" and they are almost too warm to my eye. I have replaced 60w incandescents at friends homes (without their knowledge) with these Cree LED's and asked them about them weeks later. The Cree lamps had been undetected the three times I have tried this experiment. Try one of the Soft Whites and see how you like that one.

Swapping out a 60w incandescent for one of these 10w Cree LED's, the bulb could pay for itself in less then a year depending on usage and electricity rate. At 4 hours per day and 11/cent kwh the saving is about $8 a year. Over the life of the LED you will save a lot more and get great light without the need to relamp every few months. If I had a stash of incandescent bulbs I's store them somewhere safe and sell them all on eBay one day.
 
Oh, wow, I'd wish I'd known about the soft white! I'll look out for them, because literally the only thing I don't like is the bluish tinge.

Thanks for the tip. Nostalgia or no, none of us enjoy paying a big electric bill.
 
@ kb0nes

Phil, funny you should say that about incandescent bulbs.  Holding them to sell later is exactly what I am doing with the ones I have left.  Might as well make a bunch of money off of the uninformed and those too stubborn to believe the truth about energy efficient lighting. 

WK78
 

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