# Led Traffic Lights Dying Already.



## 3rd_shift (Aug 17, 2004)

The hot Texas sun is helping to bring an end to some led traffic signals in Dallas and Grand Prairie.
They were beautiful and bright /ubbthreads/images/graemlins/huh.gif when first installed several months back. /ubbthreads/images/graemlins/smile.gif
Perhaps, too bright and overdriven too. /ubbthreads/images/graemlins/icon15.gif
But now I'm finding traffic signals with some dead or strobing leds of all colors in them and it really looks trashy at intersections. /ubbthreads/images/graemlins/sick.gif
Even some of the led crosswalk signs are now doing it. 
/ubbthreads/images/graemlins/dedhorse.gif 
Our taxdollars wasted. /ubbthreads/images/graemlins/clap.gif /ubbthreads/images/graemlins/mad.gif


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## PhotonWrangler (Aug 17, 2004)

[ QUOTE ]
*3rd_shift said:*
The hot Texas sun is helping to bring an end to some led traffic signals in Dallas and Grand Prairie.
They were beautiful and bright /ubbthreads/images/graemlins/huh.gif when first installed several months back. /ubbthreads/images/graemlins/smile.gif
Perhaps, too bright and overdriven too. /ubbthreads/images/graemlins/icon15.gif
But now I'm finding traffic signals with some dead or strobing leds of all colors in them and it really looks trashy at intersections. /ubbthreads/images/graemlins/sick.gif
Even some of the led crosswalk signs are now doing it. 
/ubbthreads/images/graemlins/dedhorse.gif 
Our taxdollars wasted. /ubbthreads/images/graemlins/clap.gif /ubbthreads/images/graemlins/mad.gif 

[/ QUOTE ]

That's sad. Excessive heat is destructive to any semiconductor device. One would think that the manufacturer would've considered this (or maybe they did but the LEDs were placed into an inappropriate fixture for the environment).

I've seen LED traffic lights around here for almost a year and they're still going strong.


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## gadget_lover (Aug 17, 2004)

I wondered about the use of LEDs in existing traffic signals. Heat is not that bad for incandescent lights, but LEDs will want some venting/cooling.

The early ones that were installed here appeared to have grounding problems signified by patches of adjacent dead, dim or flickering LEDs. About 10% had this problem which has since been fixed.

If they died so quickly, there's a good chance that they are under warranty so your tax dollars may not be wasted yet.

Daniel


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## PhotonWrangler (Aug 17, 2004)

I'm also wondering about EMI suppression. Those systems were designed with incandescents in mind, which are far more tolerant of spikes and surges.
/ubbthreads/images/graemlins/icon3.gif


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## PrimiToad (Aug 17, 2004)

So those are LED traffic lights. I've noticed them for some time now and was thinking they looked unlike bulb type lights.

All of the ones around here seem to still be bright and all LED's working. Haven't seen one yet with non-functioning LED's.


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## PhotonWrangler (Aug 17, 2004)

LED traffic signals


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## idleprocess (Aug 17, 2004)

Having glanced at the types of controls used in traffic signals (hello, big transformers and electro-mechanical relays), I'd say that dirty power, heat, and EMI/RFI are _definitely_ potential causes of failure.


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## 3rd_shift (Aug 17, 2004)

Here's more info on these in general.

http://www.cee1.org/gov/led/led_brochure.pdf


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## Mattman (Aug 18, 2004)

It doesn't sound like anyone has any first hand knowledge of why these would be failing. There's no reason the concept shouldn't work fine, so we must be dealing with a poorly designed light or defective components. I can imagine that it gets pretty hot in a box full of lit LED's hanging out in the summer sun, but if they're failing already, I agree that the manufacturers should be taking care of the problem under warranty.


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## Chris M. (Aug 18, 2004)

Along the road leading through the small town near our office are a number of pedestrian crossings that must have been built only a year or two before we moved there, and they used to have LED traffic lights - three heads per crossing. Not screw-in retrofits into older incandescent housings (UK traffic lights are different to US ones), but specially designed and built lamps. They were the first LED traffic lights I ever saw in this country. Usually sitting there on green until someone came and pushed the "stop" button by the crossing to initiate them to change, within the last couple of years I noticed ever-increasing dark patches in the otherwise even, slightly oval arrays of little 5mm LEDs. Looked like the diodes were arranged in multiple series groups, and a few of them had failed open. Why they failed, I will never know - it isn`t that hot at all here in South Wales and these were specially designed heads presumably with decent power supplies. Maybe iffy soldering? But it seems to be a quite common problem with the early generation of those British LED traffic lights since I`ve seen a few others of the same type elsewhere with similar dark spots. More recent ones I have seen have no problems yet, and there is at least one other manufacturer producing them which seem like better units anyway, no problems with those that I have seen.

I don`t drive along that road too often but recently noticed all the lights at those half-a-dozen crossings along the way had been changed.....to incandescents! And again not just retrofits but whole new heads from a different manufacturer (the other one who make LED lights here too). Which is a shame - since they sat on green most the time, the amber and red ones were still fine so they could have just replaced the green LED boards and had them back up and running. Guess the local authorities lost confidence in that "exciting new technology" based on the failures of those early greens and went back to their old low-voltage halogen favorites. Either that or they had an argument with the manufacturer over warranty replacements and wanted to "teach them a lesson".....

/ubbthreads/images/graemlins/ooo.gif


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## brightnorm (Aug 18, 2004)

"...Robust, *air tight*, weatherproof design..."

Perhaps that contributes to heat accumulation

Brightnorm


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## Saaby (Aug 18, 2004)

Saab uses a system on their engines called Direct Ignition. Basically a mini-coil over each plug. The advantage is less moving parts, less parts to wear out period, better control over the firing process, and thus better emissions.

1 big cartridge, 4 plugs, all epoxied in. Not a terrible product, but more failure prone than it should be. The suspected cause? Heat.

Striking similarity to these LED modules, supposed to be simpler and cheaper but it's not as perfect as one would think. When they figure out how to keep the LEDs happy somebody pass the knowledge onto Saab would ya?


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## ledaholic (Aug 18, 2004)

A friend of mine works for the city electrical dept. They have had several of these LED lights go bad. The ones out of warranty I have looked at have all had bad power supplies or transistors that turn on "strings" of LED's. These lamp assemblies have fairly sophisticated electronics
in them. If you can find a "bad" one, the 12 inch models have as I remember, about 177 LED's in them. A great source for expirementing.


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## jtr1962 (Aug 18, 2004)

It's power spikes that are killing the LEDs, not heat or anything else. Heat would just cause them to dim long term, and the power levels in traffic lights (a few watts) wouldn't cause enough heat build up for the observed catastrophic failure regardless. Many of these traffic light replacements are very poor designs. They simply run the LEDs off the same AC supply that powered the bulbs. All the circuit has is a full-wave rectifier and a current limiting resistor. At a bare minimum it should have a hefty filter capacitor and an active current regulating circuit. In the absence of those two things, current spikes get through, and cause damages.

I'm familiar with a similar problem with LED backlighting boards used on taximeters. These just haven't lasted the hoped for 20 years. Most last a couple of years and then the meter comes back with one or more of the LEDs open-circuited. The LED circuit boards are simply a series string of 4 green LEDs with a 120 ohm resistor. Unfortunately, the space in the meter is too small to allow designing anything better, and cost constraints would prohibit it anyway (margins are razor thin as is). I designed the boards currently in use. On a test bench at 12V they would never burn out but in cars they do thanks to lack of protection. Same thing with the LED traffic lights. Considering that the parts needed for protection are only a few dollars, if that, there is no good reason why these things aren't better protected. I'm already seeing a few dead LEDs in the crossing signs installed a few years ago here in NYC. The problem is simple-the designers of these things need to understand that an LED is not simply a drop in light bulb replacement. They also need to know it is a current-controlled device rather than a voltage controlled one. I cringe every time I hear someone ask how many volts does an LED take.


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## Robban (Aug 18, 2004)

We've had LED traffic signs in Sweden for quite some time. not sure when I first saw one but it's been a long time. And I have never seen one that flickers or have failed. Granted, our summers may not be quite as hot as "over there" though.


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## elgarak (Aug 18, 2004)

I see a lot of damaged LEDs on buses and such here in FL. But it doesn't look like like heat damage to me. Some of the LEDs are just dead. Heat damage would lead to different brightnesses across an array. jtr's explanation makes more sense -- bad circuit design.


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## ViReN (Aug 18, 2004)

I think... the Gov. Should have a look at this post... and so do manufacturers of those lights...

I remember, may be 60 years ago.... they used to "over engineer" the cars.. for durability and long lasting... (which made the car more heavy) etc....

now a days... its like... throw away cars in 2-3 years... creating more junk than ever.... 

The point is... the Attitude of Manufacturers in general.... and ofcourse the users.... 

Dont we users want New things every now and then ?.... so manufacturers respond to it (i guess) ... so its not solely their fault either....

However, I feel that some "mission Critical" applications should be robust ... (just take an example of a Hummer /ubbthreads/images/graemlins/wink.gif )

There are some things.. that we should build to last long.... Traffic Signals is one of em... 

What's the point ... if we dont design the light properly (considering all the exceptions) ... they turn out to be worse than the Incand's ... especially when there is a need to replace them.... 

A proper consideration for Lightening Spikes, Power Spikes ... & other Turbulances in voltages & currents should always be taken care of ... not to mention Heat Generated (however small it might be)... WE MUST OVERENGINEER these things.. in order to make them reliable and to make them last longer.... we should not over drive them to such an extent.. that they will just blow off... 

-ViReN


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## tygger (Aug 18, 2004)

i absolutely agree. Most products currently made are substandard. and that even shows with the new hummer(H2). from what i understand they redesigned (ie. made it cheaper) the H2 for more commercial appeal and lower production cost. no wonder the military isn't upgrading to the newer models. thats one reason why smaller companies such as Berkeley Point, etc., have loyal followings. Most mass produced products suck because people want it faster and cheaper.


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## PhotonWrangler (Aug 18, 2004)

Couldn't agree more, ViRen. Any device that is placed in a role that affects public safety should be over-engineered, the same way that medical electronics are over-engineered. One of the main reasons for LED traffic lights (besides the power savings) is supposed to be the avoidance of catastrophic failure, where such a failure could cause injuries or even deaths. There should be more than adequate heat sinking and ventilation in those things, as well as power regulation and surge protection, probably using gas-tube arrestors. I think that MOVs would only contribute to catastrophic failure as an MOV tends to fail shorted, which in turns blows a fuse, which in turn would cause the whole lamp to go out.
/ubbthreads/images/graemlins/icon8.gif


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## PlayboyJoeShmoe (Aug 18, 2004)

Lots of LED traffic signals around Houston have a few to several individual red or green LEDs out. Either I don't see a lot of yellow LEDs or none have failed.


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## Stingray (Aug 18, 2004)

[ QUOTE ]
*Saaby said:*
Saab uses a system on their engines called Direct Ignition. Basically a mini-coil over each plug. The advantage is less moving parts, less parts to wear out period, better control over the firing process, and thus better emissions.

1 big cartridge, 4 plugs, all epoxied in. Not a terrible product, but more failure prone than it should be. The suspected cause? Heat.

Striking similarity to these LED modules, supposed to be simpler and cheaper but it's not as perfect as one would think. When they figure out how to keep the LEDs happy somebody pass the knowledge onto Saab would ya? 

[/ QUOTE ]

Those types of systems have been on various cars for the last decade or two. My brother had a Nissan, I think it was a 300Z, with individual coils quite a while back, he didn't have any problems as far as I can remember.


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## PhotonWrangler (Aug 18, 2004)

[ QUOTE ]
*PlayboyJoeShmoe said:*
Lots of LED traffic signals around Houston have a few to several individual red or green LEDs out. Either I don't see a lot of yellow LEDs or none have failed. 

[/ QUOTE ]

Interesting. I wonder if this has something to do with the relatively short on-time for the yellow light?


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## 3rd_shift (Aug 18, 2004)

In Dallas Tx. the amber parts of the lights are still incandescant (almost never on, why bother converting those?), just the red and green are leds.


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## jtr1962 (Aug 18, 2004)

Same thing in NYC. They left the amber lights incandescent.

I second what everyone else said about overdesigning traffic signals. It's a mission critical application, and it costs big bucks every time you need to call a cherry picker to change the lights. No reason these should be failing so soon.


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## Sigman (Aug 18, 2004)

Our crossing signal lights seem to be holding up (except when someone shoots one...and even then we just lose a few LEDs and 90% or more of the LEDs still work. It's the hole in the housing that concerns us, allowing moisture & dirt in...holes can be plugged though!). Additionally, though the LEDs are red, we still have a plastic lens panel (to make the LEDs more visible over a wider angle) and another red plastic cover (for additional weather proofing & red awareness) that tends to shatter when shot. It's more cost effective to replace the whole assembly in the long run. I think they could be designed differently.

Seems the failures we get on installed LED lamps are the ones on our crossing gates. They aren't failing on their own...it's when a vehicle runs into one. The "weak link" seems to be the sockets, conventional in design - the internal soldered wire seems to be breaking when impacted.

Summing it up...we don't seem to be having the problems that the traffic signals seem to be as described here. I've got a friend that works for the city's traffic signal department as well. I'll give him a call and see what he says. Of course, here in Alaska...we aren't having heat much over the mid 80's (and believe me - THAT'S TOO HOT FOR ME!!)


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## Saaby (Aug 19, 2004)

[ QUOTE ]
*Stingray said:*
[ QUOTE ]
*Saaby said:*
Saab uses a system on their engines called Direct Ignition...

[/ QUOTE ]

Those types of systems have been on various cars for the last decade or two...

[/ QUOTE ]


Ok so I stand corrected. I've got to hire a better fact checker. Last time today I act like I know anything, I swear!

Anyway I still stand by my original conjecture that heat is a major factor here, either for the LEDs themselves, or the electronics that drive the LEDs.


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## iddibhai (Aug 19, 2004)

that's what CPF needs, a Fact Checker. I like the sound of that.. 

back to regularly scheduled programming. none of the LED traffic lights in my city show signs of stress, been running couple years.


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## James S (Aug 19, 2004)

They were just putting in these in the signals in Richmond when I was living there, so I didn't get to see them over a long period of time. They were really blinding at night though, considerably brighter than a regular bulb one.

Here they had them (even for amber and arrow signals) almost everywhere when we moved in a year ago, so they are over a year old now at least, possibly 2 or 3. I have not seen a single dead LED or any other obvious problems with any that I've driven under. And I've been looking closely the last few days since noticing this thread /ubbthreads/images/graemlins/smile.gif

It's possible that a manufacturing defect is messing with a whole batch of them somewhere, but more likely it's like everything else, you get what you pay for. There are cheap ones, and there are long lived ones and any information on the overlapping of the 2 categories came from the marketing department /ubbthreads/images/graemlins/grin.gif


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## ledaholic (Aug 19, 2004)

They are over-engineered. If I can find the control board out of one, I'll post some pics. There is a governing body for traffic signals, local governments can't just throw in some kind of lamp, they have to meet pretty tight requirements. LED lamp assembly's are still fairly new to traffic lights. In time they will get better or will be replaced with something else.


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## gadget_lover (Aug 19, 2004)

Several posts stated that heat would *only* cause LEDs to dim. Unfortunately, this is not true.

There are three things that bother semiconductors; heat, incorrect voltage and vibration. The advent of potted electronics (ICs, LEDs, etc) has made vibration much less of a problem, but the other two are still killers.

When a semiconductor heats up it's electrical properties change. That property is actually one of the definitions of a semi-conductor according to a 1970's textbook. If the parts' characteristics change too much the current will excced the design's capacity and the part will melt internally. 

Overvoltage will usually cause death by pushing too much current. See above Way over voltage will cause internal arcing, again death by melting.

Heat builds up quickly in an enclosed container. If you think that there's not much heat from a "few watts" used in the traffic light you can do your own experiment. Drop an arc AA or other single LED light in a thermos bottle, then seal it and watch TV for 1/2 hour. I'm pretty sure it will be uncomfortably hot by then.

Of course, I could be wrong /ubbthreads/images/graemlins/smile.gif

Daniel


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## elgarak (Aug 19, 2004)

Well, I referred to the error mode I observe. I see the following: An array of 5(let's say) 0 LEDs. 25 on the left side do not give off any light (when observed during daylight), the right half is very bright. Ageing the LEDs with overheating would not result in this error. One should see varying brightness levels over the array. If one side of the array is hotter than the other side, one should see gradually changing brightness from one side to the other. Not the sharp edge of LEDs on and off I observe.


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## IsaacHayes (Aug 19, 2004)

I belive it probably is poor circuit design. And there are lots of manufactors out there. I know I've shipped some led lights back for D.O.T. that I assume were broke. Also it seems they replaced or upgraded to a newer model LED lights as they don't have the same ones anymore in the lights. Some even have diffusers so it doesn't blind you at night. Some may also be luxeon behind there, as it seems to be even more diffused and not a pin point source, also a slightly different color than the other leds...

We also have Yellow LED ones now...


One thing though, in winter, snow doesn't melt off of the LED's, making it hard to see the lights! Anyone eles notice this?


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## The_LED_Museum (Aug 19, 2004)

As I understand, some LED traffic light fixtures have heaters to melt the snow. But not all of them do; that's the problem.


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## ledaholic (Aug 20, 2004)

I found the controller-powersupply board for a 12in red led traffic lamp assembly. I have a picture if anybody is interested. If someone will post it, I'll email it.
Bob


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## 3rd_shift (Aug 21, 2004)

Better yet, go here;
www.photobucket.com
Once your pic is uploaded there, 
(it's easier than I'm making it look /ubbthreads/images/graemlins/tongue.gif ) ,
then highlight the whole url to it, right click copy, then right click paste it here on cpf . /ubbthreads/images/graemlins/smile.gif
We then can see it. /ubbthreads/images/graemlins/ooo.gif
Done and done. /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/clap.gif 
Anyways, on with the show. /ubbthreads/images/graemlins/wink2.gif 
Edit: Oh yeah, if you need to resize the pic down to 640x480, go here for a good free photo editor called irfanview. /ubbthreads/images/graemlins/wink.gif 
edit again: too much hassle to learn in one day? /ubbthreads/images/graemlins/banghead.gif 
send the photo to [email protected] 
I'll fix it up real good for ya pardner. /ubbthreads/images/graemlins/grinser2.gif


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## NewBie (Aug 21, 2004)

[ QUOTE ]
*PhotonWrangler said:*
LED traffic signals 

[/ QUOTE ]


Yeah, LumiLEDs is also one of the major players in traffic light signals.

http://www.dialight.com/contents.tpl?page=contents&sub=contents&sku=19

http://www.dialight.com/subs.tpl?page=transportation&cat=Traffic

Here is a study on LED traffic signals:
http://cogprints.ecs.soton.ac.uk/archive/00002486/01/led.pdf

I spoke to one of the presenters at a LumiLEDs (their luxeon and their superflux) conference about failures in LEDs in the field, and he actually used traffic signals as an example. For failures they had seen, there were two big issues. One of the major factors that he indicated was corrosion in the electronics from moisture intrusion, water intrusion, exposure to humidity, and poor cleaning after assembly (folks had used no-clean flux (which is a whole issue in and of itself)), some had used nothing but bare boards and did nothing to protect the electroncs (such as potting or conformal coating). 

He indicated the heat failures seemed to be due to a mis-understanding of the environment where they were used (imagine how hot the fixture that is painted flat black gets in the sun), and poor understanding of removing the heat in the first place. 

Here is a report from various cities and their comments of their experiences with them:
http://www.dot.wisconsin.gov/library/research/docs/tsrs/tsrledsintrafficsignals.pdf


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## ViReN (Aug 21, 2004)

I think, Instead of potting... If they use Silicone Rubber RTV Sealent to seal off the parts (including the LED's in to a single block... will solve most of the problems ... and as far as the heat sinking is conserned... The Heat Sink Itself can be Outside... and other parts sealed IN... 

If there is a need to rework... removing RTV isn't difficult... moreover... RTV Sealent is almost transperent... (though i dont know effects of Sunlight tht might be falling on it... (does it get yellow ??)

-ViReN


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## NewBie (Aug 21, 2004)

During one of the LumiLEDs hands-on thermal labs, they had a traffic light some vendor was making from luxeons, where the outer cone had a molded in sheet of metal to dissipate the heat. 

Viren, humm, RTV is potting (it can also be conformal coating.)


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## ledaholic (Aug 21, 2004)

3rd shift,
Photobucket said I had to wait till later to sign up so I put it here http://tinypic.com/2ujiu . Just in case it doesn't work, I'll send it to you also. The lamp assy I took this controller from was a 12 inch red light with 177 5mm bright red LED's. There was no heat sinking at all inside the assy. The LED's were mounted directly to the pcb the rest of the components (transistors to turn on the individual strings of LED's)were on. I don't have the pcb anymore, but if I come up with another one, I'll post a pic

Bob


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## 3rd_shift (Aug 21, 2004)

Here's the pic of that circuit board powersupply.





[image]http://tinypic.com/2ujiu[/image] *Rats, it didn't work from that url.* /ubbthreads/images/graemlins/icon3.gif


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## PhotonWrangler (Aug 21, 2004)

Ok, I see an MOV (RV1) next to the input inductor. I also see a big ol' transistor (Q5) in the upper-left area that looks a little, ah, stressed.


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## gadget_lover (Aug 22, 2004)

[ QUOTE ]
*elgarak said:*
Well, I referred to the error mode I observe. I see the following: An array of 5(let's say) 0 LEDs. 25 on the left side do not give off any light (when observed during daylight), the right half is very bright. Ageing the LEDs with overheating would not result in this error. One should see varying brightness levels over the array. If one side of the array is hotter than the other side, one should see gradually changing brightness from one side to the other. Not the sharp edge of LEDs on and off I observe. 

[/ QUOTE ]

While I understand your assertion, there are many failure modes that can occur from temperature;

A set of LED's in series will all go out when one overheats and goes open.

Frequent change of temperature can cause the boards to expand and contract, breaking traces and causing bad contact at connectors.

Overheating may also cause the driver / power supply electronics to fail in interesting ways.

Daniel


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## PlayboyJoeShmoe (Aug 22, 2004)

I notice even more after this thread.

The Red signals around here are one of two types. Straight runs of leds, or a sunburst array.

I haven't seen any complete lines out on the straight runs, but individual leds (almost always around the outside edges) are out. Maybe two in a row sometimes. Same goes for the sunburst.

I actually don't notice the greens as much, since I'm boogying when I get one!

And a lot of intersections have yellow leds too.


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## ViReN (Aug 22, 2004)

3rd_shift .. The Electronics is THAT BAD ???? 

Oh Please.... Even the Cheap Chinese Telephones look much better (in electronic components & Layouts).... and they sure can handle more shocks & humidity.. than that bord picture....

To Me, It looks like, Its some where in old 70's PCB Board.. where they used to have that kind of placement.. (hand placed components???)...

Oh Look at the ceramic capacators... & the way resistors are placed !!! ....

It sure does not make any difference in the functionality.. but sure could impact the performance & Reliablity.....

If that is how (all) Traffic Signals have supplies... then there is NO USE of AIRBAGS & Seat belts... after all (if a light fails to show RED) who is gonna stop ??? Accidents are inevitable !!!....

I am really sorry to see that board.. wish i had never seen it... EVER !

3rd_shift , Just take a look at some good medical electronic equipment.... you will know what i am talking about... 

If medical equipment is a matter of life and death.. WHY NOT TRAFFIC SIGNALS ???? Why such pathetic boards... ?????

When there is LOT of space.. is there any POINT in putting STANDING RESISTORS ????

WHATS THE USE OF DOUBLE SIDED PCB ????? what.. if by shock... 2 resistors get short... (which may drive the Transistors that DRIVE LED's !!!!!!!!!) and WHAT IF THAT LIGHT IS A GREEN ONE ? ... 2 GREEN LIGHTS... 2 FAST CARS... both see green... and THATS ALL IT TAKES DUDE !!!...

Please forgive me for using Caps... but.... i cant keep cool man... not at all.... ( i aint angry on any of CPF guys... please let this be known clearly... but angry... on... the way it has been designed)

I have an OLD u.p.s. (10 years back) ... and they have used floor resistors... NONE of em is standing... (though home computer u.p.s. is not LIFE Critical Application nor it is going to handle shocks(physical shocks .. wether / storm related)) ... I also understand that the resistor leads might be strong.. but they are NOT THAT strong... seen Bouncing Signals.. when there is a thunder storm... ???

Oh Let Quickbeam & C.J. Do some testing on these Lights too... I am sure .. they wont get any more than Z E R O Stars !!!

ViReN


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## HarryN (Aug 22, 2004)

There are a number of LED manufacturer's that produce LEDs with a wide range of lifetimes. The lifeimes we are used to looking at for monochromatic Luxeons like RED / Green (nominally 100K hours to 80 - 90% initial brightness) are quite deceivingly applied to 5mm LEDs. AFAIK, only really premium brand and quality 5mm LEDs come even close to 50 % of this performance. Most of the curves I have seen are more like 50% brightness after 5 - 10K hrs. 

Especially with 5mm red LED die prices in the US $ 0.005 - 0.02 range, pressure to cut corners in product development and production and is quite high. Reliability is a common victim.

Another commonly applied cost cutting method is to substantially over drive the LEDs in the fixture to meet the required brightness spec, then blame the LED maker when product lifeime is less than specified. (this is commonly discussed at LED conferences)

Last but not least, humidity also degrades LEDs, along with the more commonly discussed heat. There is a famous case study of LED traffic light installations in Singapore, land of heat and humidity (similar to Houston). As it turned out, none of the suppliers that actually knew what they were doing would bid on the project because the lifetime specs could not be achieved. Guess who got the order ? Guess how long the LED traffic lights lasted ?

In California, the most used signal light is RED, which is of course key to our ultra efficient traffic control system. /ubbthreads/images/graemlins/icon15.gif Power consumption was the main reason for converting these to LED first. 

Amber is hardly ever on, and our traffic control friends carefully time this signal to be on a random amount of time so that the traffic cameras can issue tickets in the most efficient manner possible. LED use in this light is not necessarily cost effective, but potentially reduces labor to change the bulb.


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## jtr1962 (Aug 22, 2004)

[ QUOTE ]
*HarryN said:*
AFAIK, only really premium brand and quality 5mm LEDs come even close to 50 % of this performance. Most of the curves I have seen are more like 50% brightness after 5 - 10K hrs. 


[/ QUOTE ]
Are you 100% sure of this? I know that 5mm whites driven to spec last about 5,000 to 10,000 hours, and smaller wavelength colored LEDs (UV, blue, cyan) also last less than 100,000 hours (but much more than 10,000 except for UV). Red, orange, amber, and green _should_ last at least 100,000 hours. The same tests which were performed on 5mm whites also used 5mm reds as a control. They even stated that it had been well established that reds lasted at least 100,000 hours.

I'm wondering exactly how cutting corners can affect lifetime. The usual degradation mechanisms are blackening of the epoxy (not the main factor in long wavelength LEDs), phosphor degradation (again not applicable except in white), and degradation of the die itself. Since many types of semiconductors are mass produced at low costs (i.e. diodes, transistors), and these all last decades if driven to spec, I don't see how low-cost mass production can affect _die_ lifetimes. This leaves us with only two other failure mechanisms-substandard wire bonds and humidity entering the package due to substandard encapsulation. I'm not counting heat since I said the LEDs were driven to spec. Both of these will certainly shorten the life on average, but not through gradual dimming. Rather, we would have catastrophic failure of a greater than usual number within the first few hundred hours of life (termed _infant mortality_). The remainder that survive will last 100,000 hours because even cutting corners with packaging, you will need a majority of good units to make production worthwhile. Or put another way, if you cut corners too much, so many of your LEDs will fail in the first few hundred hours than you will put yourself out of business.

The only difference between low cost and higher cost LEDs will be a higher than normal infant mortality rate. Provided you "burn-in" finished products for a few hundred hours, then you should catch most of the failures before they go out in the field. Evidently, some traffic signal manufacturers are using cheap LEDs and not doing this. Nothing necessarily wrong with cheap LEDs, BTW, provided you accept a higher than usual infant mortality in return for paying less. I'm perfectly confident the cheap white LEDs I buy from HK for $0.25 each will last as long as $1.50 Nichias. I'll just get a few more failures in the first few hundred hours. Truth be told, given the infant mortality rate of most types of electronics, I would probably have to use tens of thousands of LEDs to notice one infant mortality failure even with the cheaper LEDs. Of course, when you're dealing with thousands of traffic lights each with 100+ LEDs you're going to have some failures.


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## jtr1962 (Aug 22, 2004)

I also wish to add that the control board pictured earlier leaves a lot to be desired. Those filter caps are too small to do any good, and it looks like the transistors just turn on strings of LEDs. What regulates the current-a simple resistor? /ubbthreads/images/graemlins/frown.gif If I had to hazard a guess, I'd say many of the failures are not the LEDs themselves, but something on the circuit board causing a string to go out.

For what it's worth, so far I've only seen a few bad LEDs on NYC's crosswalk signs, and these seem to be most the orange-red ones rather than the white ones. I haven't seen any traffic signals with noticable dark areas yet. Maybe these things really will last 25 years if designed correctly. I hope so, because I think traffic signals are a testbed for the next thing to be replaced by LEDs once efficiency exceeds that of sodium vapor lamps-street lights. I certainly look forward to the day we have nice white LED street lighting in place of those hard to see under sodium vapor lights.


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## HarryN (Aug 22, 2004)

There are some fundamental differences between a common Si transistor based device, and an LED. For one, a Si device is built in nearly a perfect material - single crystal Si. The equivalent material does not exist for LEDs. This very low cost Si material, with exceptional crystal properties, is at the heart of high reliability devices.

For seconds, Si devices have been around a long time, the third tier, lower reliability players are all out of business. Also, early on, IBM and the car companies really pushed Si device reliability very hard.

An LED is grown in thin, much less than perfect crystaline layers. ONE, of the many factors that affect LED lifetime is just how well this part of the process is performed. The IP related to this is a closely held secret, and only companies willing to invest in serious R and D programs have done the groundwork to have this IP. There are still quite a few fly by night operators in the LED business.

You can see the effect of this IP investment if you follow a Lumileds, Cree, or Nichia data sheet for 12 - 18 months. The "same" LED gets brighter, specs tighten, Vf decreases, etc.

I would have to do some digging to find the paper, but Dr. Heng Liu, formerly of AXT, presented at a conference approx 18 months ago on this very subject, comparing blue, 5mm LEDs driven at spec conditions, and comparing "output" vs "time". There is a pretty dramatic difference between the shape of the curves from the tier 1 vs other suppliers.

Part of the lifetime spec question is based on when you call a "end of life". I believe that Lumileds specs EOL when they reach approx 90% of initial brightness. Many others use 50 % of initial brightness.

AFAIK, LEDs usually either work or not, and are not really subject to a lot of burn in testing.


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## NewBie (Aug 23, 2004)

70% for LumiLEDs Luxeons.

DS25 (1W datasheet)
Lumileds projects that Luxeon products will deliver on average 70%lumen maintenance at 50,000 hours of operation.This performance is based on independent test data, Lumileds historical data from tests run on similar material systems,and internal Luxeon reliability testing.This projection is based on constant current 350 mA operation with junction
temperature maintained at or below 90 °C.

http://www.lumileds.com/pdfs/protected/DS25.PDF

DS45 Datasheet (Luxeon III)
Lumileds projects that Luxeon III products will deliver, on average,70%lumen maintenance at 50,000 hours of operation at a 700mA forward current or 

50% lumen maintenance at 20,000 hours of operation at a 1000 mA forward current.

This performance is based on independent test data, Lumileds historical data from tests run on similar material systems,and internal Luxeon reliability testing.This projection is based on constant current operation with junction temperature maintained at or below 90 °C.

http://www.lumileds.com/pdfs/DS45.PDF

DS40 (Luxeon V)
...and lifetimes greater than 50X conventional flashlight
sources over 500 hours compared to the typical 20 hour life for an incandescent bulb.

Heatsink Temperature 35C Current 700mA Average Lumen maintainance after 500 hours - 90%

Heatsink Temperature 75C Current 700mA Average Lumen maintainance after 500 hours - 75%

Heatsink Temperature 85C Current 600mA Average Lumen maintainance after 500 hours - 65%

http://www.lumileds.com/pdfs/protected/DS40.PDF

<font color="red"> *(pay close attention to the most recent change in the Lux V datasheet here)* </font> 

This is a great read for anyone wishing to understand the issues involved and how they affect the Luxeon:
http://www.lumileds.com/pdfs/RD25.PDF


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## gadget_lover (Aug 23, 2004)

What HarryN said makes a lot of sense. Not only does it match my scketchy memory of semiconductor construction but I have visited with HarryN and believe he has the credentials and experience to back up his statements.

Daniel


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## jtr1962 (Aug 23, 2004)

I don't doubt HarryN's credentials. I'm just saying that this is the first I've heard of this difference in lifetime between different LED suppliers. And how does one know which chips end up in the LEDs you buy anyhow? For all I know the cheap HK LEDs may be using chips from Cree or Nichia. I'm planning on doing some long term testing of the various colors I have. I already know UV dims by quite a bit even after a few hundred hours, but this is a problem common to all UV LEDs as far as I know, or else they would be used in white LEDs instead of blue. Anyway, I'm finding this all very disturbing, especially if the LEDs in traffic lights don't last the claimed 100,000 hours.


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## gadget_lover (Aug 23, 2004)

I see your point, jtr1962. There is no way to know if you are getting top quality products in ANY category these days. With so much outsourcing of manufacturing, only a purchase directly from the manufacturer will provide any degree of assurance. Another thread quoted buying 1000mah battery packs only to find that they had 600mah cells inside.

I'm not sure why people worry about traffic signals as something extra critical. Ours don't have emergency power, and we live right through it. The traffic signals in the US are failsafed in a way. If the red does not light up, you are still supposed to stop because you don't have a green light.

I thought that blue was used to complement the yellow phosphor. I culd be wrong. They might have chosen a yellow phosphor to suplement the blue.

Daniel


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## jtr1962 (Aug 23, 2004)

Actually the yellow phosphor is to complement the blue LED (combined they appear "white" to us even though it's not a perfect blackbody white).


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## HarryN (Aug 23, 2004)

[ QUOTE ]
*jtr1962 said:*
I don't doubt HarryN's credentials. I'm just saying that this is the first I've heard of this difference in lifetime between different LED suppliers. And how does one know which chips end up in the LEDs you buy anyhow? For all I know the cheap HK LEDs may be using chips from Cree or Nichia. I'm planning on doing some long term testing of the various colors I have. I already know UV dims by quite a bit even after a few hundred hours, but this is a problem common to all UV LEDs as far as I know, or else they would be used in white LEDs instead of blue. Anyway, I'm finding this all very disturbing, especially if the LEDs in traffic lights don't last the claimed 100,000 hours. 

[/ QUOTE ]

Hi jtr. Actually, my career has shifted over time away from my chem eng roots to being more qualitative than in the past - now I just know enough to be dangerous. The great thing about having Newbie in the forums is he is always there to fix our errors with real details.
/ubbthreads/images/graemlins/smile.gif He seems to know this stuff in and out.

Gadget is right, you are going to need to really understand your source all the way back to the die provider if you want to really be in control of your results. There are a few firms that are "buyer / packagers", that have pretty tight specs on their supply chain - Agilent is one of them, and there are a few others. (yes, believe it or not, Agilent typically buys die that meet their specs and has them packaged- usually not Lumileds die, even though they own 50 % of the firm.)

PM me if you would like to reach some people who have done similar testing.


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## NewBie (Aug 24, 2004)

[ QUOTE ]
*jtr1962 said:*
I don't doubt HarryN's credentials. I'm just saying that this is the first I've heard of this difference in lifetime between different LED suppliers. And how does one know which chips end up in the LEDs you buy anyhow? For all I know the cheap HK LEDs may be using chips from Cree or Nichia. I'm planning on doing some long term testing of the various colors I have. I already know UV dims by quite a bit even after a few hundred hours, but this is a problem common to all UV LEDs as far as I know, or else they would be used in white LEDs instead of blue. Anyway, I'm finding this all very disturbing, especially if the LEDs in traffic lights don't last the claimed 100,000 hours. 

[/ QUOTE ]

Dunno who HK companies are utilizing. Some Asian LED makers are in fact using CREE die, as well as Toyoda Gosei, the CREE die are distributed and rep'd by Sumitomo, the last purchase was for 160,000,000.00 dollars of LED die (the tiny chip inside the LED). There are quite a number of island based die makers too though....

In fact, Toyoda Gosei has even made die for LumiLEDs.

Some of the big factors in LED life in recent years will be in the packaging. Die attach adhesive, and how well it resists light (especially UV) (some are actually soldering down the die themselves, where Luxeons have a die that is floating on I think it was 16 solder balls that rest on a ESD or Zener diode, dunno if they solder their zener to the heatsink though, unlike others who do), in whites, the life of the phosphor (phosphors also have a lifetime), the filler material often used to make the body from (as in 5mm)- as most by know know the epoxy yellows with time/temperature/light exposure, some fill with versions of non-yellowing silicon (for example, GE's X-14 LED silicone) (such as newer Nichia's, CREE XLamps, LumiLEDs Luxeon, and OSRAM's Dragon) some have an acrylic dome (seems those'd yellow too with time) to cover the silicon gel, others use no dome, or even a glass lens. Additionally, you'll find some even in a metal can with a glass lens, and Microsemi was pursuing a metal leaded, and all glass package (no goop, gunk, plastic). 

I've querried Toyoda Gosei (who makes a LED with a UV die and RGB phosphor, which doesn't rapidly degrade like everyone said it would), Nichia, and CREE, none of them have ever heard of the UV attacking the DIE itself, unsure where that rumor came from.

In fact, you'll find 20,000 hour UV LEDs here:
20,000 hour UV LEDs 

Oh, there is a huge difference between LED suppliers, as they utilize different packaging, and I have some white LEDs from an asian source that keeled over an barely glow anymore, even ran within their specs. The quality of the die itself, can't tell you much about that.

The reason blue is used instead of UV is the YAG phosphor is matched for the blue. The folks like Toyoda Gosei, who have been making a UV based White LED utilize a special version of RGB phosphor. The color rendering is much higher than the blue die-yellow phophor, and pictures taken where those are utilized as a light source look *much* more natural.

You can read more here:
http://www.microlamps-tg.com/
http://www.microlamps-tg.com/html/Prod_white_compare.htm

Datasheet:

True White Hi 

Catalog:
http://www.microlamps-tg.com/html/Cat04_01.htm


As far as the 100,000 hours, alot of it has to do with the skill and experience of the companies that designed the traffic light. This is one area where buying from the cheapest bidder can result some very unhappy campers. It's these companies that will give LEDs a bad rap. Just like the millions of CFL bulbs made by GE and Sylvannia that were only lasting a few months for many folks (yeah, other brands had the issue, but those two companies really showed how incompentent they have become).

You can even underdrive the LEDs and use more of them, to extend their lifetime....been there, done that.


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## auburn (Mar 15, 2009)

I am working on a paper on the LED traffic light failures. Anybody have pictures of failed traffic lights in your area? If you do can you post them? Thank you.


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## Lightingguy321 (Mar 16, 2009)

ledaholic said:


> A friend of mine works for the city electrical dept. They have had several of these LED lights go bad. The ones out of warranty I have looked at have all had bad power supplies or transistors that turn on "strings" of LED's. These lamp assemblies have fairly sophisticated electronics
> in them. If you can find a "bad" one, the 12 inch models have as I remember, about 177 LED's in them. A great source for expirementing.


 

12" GELcores from GE have 192 LEDs in them. I can't recall what ecolux 12" modules have in them numbers wise


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## RODALCO (Mar 18, 2009)

In New Zealand we had initially the orange LED clusters failing. ( about mid 2005 ). Now I see that some green and red LED clusters are affected as well.

I got hold of a couple of broken red and green ones via someone I know in the traffic signal department.
There are different arrays of LED's in use, 230 Volts direct with a fancy electronic supply which drives the LED's at their max current of 20 mA's each. in parrallel lots of 4, in series strings.
Some lamps are arranged in a nice circular star pattern while others are leds in lines behind freznell lenzes.

Typically one LED fails and shorts out the other three hence 4 LED's are out on the board.
By replacing the one LED, the string works again properly.
I use a red and green as growing lights for my mango's and plant cuttings.

Will take some photo's soon and post. Also from some failed ones I'm aware of in my area.


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## RODALCO (Mar 18, 2009)

http://farm1.static.flickr.com/55/131301311_b0b65e12ab_o.jpg

Orange LED string with 4 LED's failing at Mc Leod Rd te Atatu, Auckland, NZ.


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## greenlight (Mar 18, 2009)

I see mostly greenlight failures, but I'm usually moving too quickly to get a picture.


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## ledstein (Mar 18, 2009)

Maybe to the people that build those traffic lights and to those that bought them real lifetime data for the leds didnt exist. 

Data like this: https://www.candlepowerforums.com/threads/224624

Might have made them understand what they are paying for.


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## bshanahan14rulz (Mar 18, 2009)

perhaps they knew the likelihood of one (and hence 4) LED failing and decided "eh, they're pretty cheap, and 4 LEDs failing is nothing compared to saving money"

Plus, I bet it's tricky running off mains


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## RODALCO (Mar 20, 2009)

This one I took today, in te Atatu Rd, New Zealand, only 4 led's are out.

Usually you have to be very quick to take a photograph while in the car. Too dangerous to stand on the middle of the road.

http://farm4.static.flickr.com/3601/3368891617_73caf86ae5.jpg?v=0

One below is from a cluster of red LED's which I use for my plants.

http://farm4.static.flickr.com/3636/3369718522_572f22ded6.jpg?v=0


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## RyanA (Mar 20, 2009)

Same here. Maybe the green is just on more often, or the lifespans are shorter. I'd imagine that at an intersection with an inductor coil and where one road is much busier than the other then the green would be on most of the day, likewise with the red on the perpendicular road. Perhaps it has gone unnoticed because it is less likely for one of us to travel one of those roads. It might be worth a trip down the less-driven perpendicular road to see if the same is true of the reds. I suppose the yellow would last the longest in most cases.


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## 2xTrinity (Mar 22, 2009)

RyanA said:


> Same here. Maybe the green is just on more often, or the lifespans are shorter. I'd imagine that at an intersection with an inductor coil and where one road is much busier than the other then the green would be on most of the day, likewise with the red on the perpendicular road. Perhaps it has gone unnoticed because it is less likely for one of us to travel one of those roads. It might be worth a trip down the less-driven perpendicular road to see if the same is true of the reds. I suppose the yellow would last the longest in most cases.


Another is that the green LEDs are likely less efficient than the other colors. Particularly for older fixtures that are several years old, green LED efficiency was quite low back in those days, so my guess is they might be driven harder than the reds in general. Very very few engineers I know are aware of how sensitive LEDs are to overdrive, that is, how expected life of LEDs (particularly epoxied 5mm LEDs) drops so severely due to increasing the current.

If I were designing street light assemblies though, I would want to overengineer the fixture assuming a worst case scenario: make the fixture robust enough to survive a 100% ON duty cycle, with record high ambient temp and humidity, and dirty mains power supply. Also use circuit boards aimed at surviving wide temperature swings -- Many of the failure modes I've seen in some of the oldest LED traffic lights (at least 10 years old) are single strips of flickering off an on, which wuold suggest a broken wire or trace on the circuit board, probably from thermal expansion/contraction over the years, causing a break on the circuit board.

For one, most of those fixtures have relatively few 5mm LEDs spread pretty far apart. They have room to fit more than 10x as many LEDs on the surface if they wanted to. IMO a reasonable approach would be to use 4x more LEDs in the same surface area, and drive them at maybe ~20% of the current as before, and get the same overall brightness with substantially less heat. 5mm LEDs are not that expensive, the extra unit price of those 5mm LEDs and circuitry would likely be less than the cost of the labor to replace something like traffic lights even once. Not to mention reliability/safety.


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## Apollo Cree (Dec 20, 2009)

I'm glad to have found this thread. I've been wondering about why so many of the LED traffic signals have individual LED's out. I've had a snicker or two about our local idiot tree hugger city council buying into a "green" technology that doesn't work. 

However, the LED lights are usually brighter than the incandescent lamps they replace. I've never seen an LED signal where there were enough of the lights out to make it hard to see the signal color. Even the worst LED signal has been brighter than the average incandescent. 

The incandescent traffic signal bulbs do fail completely when they burn out, and the LED signals seem to loose some light, but still have more than enough light to do the job. 

Do we have a real problem with LED traffic lights, or just something that looks bad?


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## Yoda4561 (Dec 20, 2009)

It's certainly a real problem, but less of one I think than the old Incan traffic lights had. Like you said the visibility even with half the lights out is still MUCH better during daytime than incan traffic lights. But that doesn't mean that it's "okay" for half the lights to be out, it's absolutely preventable, and I'm sure that most newer led traffic lights made in the last couple years have fixed the problem(or at least it should be fixed, there's no excuse now really).


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