Led Traffic Lights Dying Already.

3rd_shift

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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
 

PhotonWrangler

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[ 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.
 

gadget_lover

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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
 

PhotonWrangler

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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
 

PrimiToad

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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.
 

idleprocess

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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.
 

Mattman

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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.
 

Chris M.

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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
 

brightnorm

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

Perhaps that contributes to heat accumulation

Brightnorm
 

Saaby

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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?
 

ledaholic

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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.
 

jtr1962

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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.
 

Robban

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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.
 

elgarak

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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.
 

ViReN

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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
 

tygger

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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.
 

PhotonWrangler

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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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