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Thread: Led Traffic Lights Dying Already.

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    Flashaholic* 3rd_shift's Avatar
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    Default Led Traffic Lights Dying Already.

    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 [img]/ubbthreads/images/graemlins/huh.gif[/img] when first installed several months back. [img]/ubbthreads/images/graemlins/smile.gif[/img]
    Perhaps, too bright and overdriven too. [img]/ubbthreads/images/graemlins/icon15.gif[/img]
    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. [img]/ubbthreads/images/graemlins/sick.gif[/img]
    Even some of the led crosswalk signs are now doing it.
    [img]/ubbthreads/images/graemlins/dedhorse.gif[/img]
    Our taxdollars wasted. [img]/ubbthreads/images/graemlins/clap.gif[/img] [img]/ubbthreads/images/graemlins/mad.gif[/img]

  2. #2
    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    [ 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 [img]/ubbthreads/images/graemlins/huh.gif[/img] when first installed several months back. [img]/ubbthreads/images/graemlins/smile.gif[/img]
    Perhaps, too bright and overdriven too. [img]/ubbthreads/images/graemlins/icon15.gif[/img]
    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. [img]/ubbthreads/images/graemlins/sick.gif[/img]
    Even some of the led crosswalk signs are now doing it.
    [img]/ubbthreads/images/graemlins/dedhorse.gif[/img]
    Our taxdollars wasted. [img]/ubbthreads/images/graemlins/clap.gif[/img] [img]/ubbthreads/images/graemlins/mad.gif[/img]

    [/ 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.

  3. #3
    *Flashaholic* gadget_lover's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Led Traffic Lights Dying Already.

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

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    Default Re: Led Traffic Lights Dying Already.

    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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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Led Traffic Lights Dying Already.


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    Flashaholic* idleprocess's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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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    Flashaholic* 3rd_shift's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    Here's more info on these in general.

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

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    Default Re: Led Traffic Lights Dying Already.

    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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    Flashaholic* Chris M.'s Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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".....

    [img]/ubbthreads/images/graemlins/ooo.gif[/img]

  11. #11

    Default Re: Led Traffic Lights Dying Already.

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

    Perhaps that contributes to heat accumulation

    Brightnorm

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    Default Re: Led Traffic Lights Dying Already.

    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?

  13. #13
    Flashaholic* ledaholic's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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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    Default Re: Led Traffic Lights Dying Already.

    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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    Default Re: Led Traffic Lights Dying Already.

    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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    Default Re: Led Traffic Lights Dying Already.

    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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    Default Re: Led Traffic Lights Dying Already.

    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 [img]/ubbthreads/images/graemlins/wink.gif[/img] )

    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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    Default Re: Led Traffic Lights Dying Already.

    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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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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.
    [img]/ubbthreads/images/graemlins/icon8.gif[/img]

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    *Flashaholic* PlayboyJoeShmoe's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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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    Flashaholic* Stingray's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    [ 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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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    [ 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?

  23. #23
    Flashaholic* 3rd_shift's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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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    Default Re: Led Traffic Lights Dying Already.

    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.

  25. #25
    * The Arctic Moderator * Sigman's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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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    Default Re: Led Traffic Lights Dying Already.

    [ 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.

  27. #27

    Default Re: Led Traffic Lights Dying Already.

    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.

  28. #28
    *Flashaholic* James S's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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 [img]/ubbthreads/images/graemlins/smile.gif[/img]

    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 [img]/ubbthreads/images/graemlins/grin.gif[/img]

  29. #29
    Flashaholic* ledaholic's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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.

  30. #30
    *Flashaholic* gadget_lover's Avatar
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    Default Re: Led Traffic Lights Dying Already.

    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 [img]/ubbthreads/images/graemlins/smile.gif[/img]

    Daniel

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