Houston started converting to LED traffic lights about, oh, a year, maybe a year and a half ago. The priority seems to be red lights first, then caution lights and lastly Go, Man greens.
I like 'em.
But.
I’ve noticed while sitting at the lights that the early installations now have an - estimated - 7-9% failure rate after what seems like a very short time for a traffic device of which there are probably a couple of hundred thousand in Houston.
I’m talking about the individual LEDS, of which I’d guess there are around 200 or so in a single red light. After a year plus, most of them seem to have about 15-20 dead ones.
What’s the maintenance deal on these babies? Surely they’re not planning on replacing individual dead LEDS in situ? So they must be planning to pull the light and do a shop refit.
I guess my question is really more like, are we going to find out that traffic light LEDs just don’t cut it economically?
That’s kind of funny, because here in St. Louis, I haven’t noticed any individual burned-out LED’s - but there are a few LED lights that are out completely only a short time after installation. Is there a fuse somewhere that needs replacing in that situation?
And I believe the main benefits of LED use are lower energy consumption and much better visibility than regular bulbs. I don’t know if their longevity is that much better than the standard traffic light bulb, if they are going out one by one like that.
It could be that many of the signals in your area contain components from a bad batch, although if the fault is widely evident in more than one of the colours, it would more or less have to be part of the driving circuitry or the board itself that was faulty, rather than the LEDs.
Does anyone know whether the LED arrays are directly soldered to a PCB, or are they plugged into a grid of sockets to make individual replacement simpler?
I seriously doubt that the individual LEDs can be replaced. That would increase the cost of the lights by a lot. One of the big benefits of the LED lights is that they do not have to be replaced as often as incandescent bulbs saving the city labor costs. I don’t see cities replacing individual LEDs in the bulbs as that would cost to much.
I wouldn’t be surprised if the pattern of failures of LED lamps was a lot like LCD screen pixels - a small number fail very quickly, the majority last nearly forever. For LCD screens, this led to most manufacturers saying that a small number of “dead pixels” (like up to 5) was acceptable, and assuring you that after using it for 30 days all the ones that are going to die have died. Possibly, a similar line of reasoning applies to the traffic lights, and nobody’s going to care if a couple of LED’s fail early because the rest will have a very long life.
Socketing the LEDs would also put a serious kink in the long-term reliability of the modules. These things are hanging out in the wide open in pretty awful conditions - rain, fog, contamination from air pollution, shaking in the wind, daily temperature changes, etc. Assuming 200 individual LEDs in a module, there would be 400 contacts, each just waiting to corrode.
I’m guessing the early failures are from a maker that doesn’t do extensive “burn-in” testing of the things.
Here in SC, we’ve had the LED lights close to a year now, and there are a few lights where I have seen 5 or 6 individual LEDS burned out already. Also, coincidentally, our lights started out with the red ones, followed by the green, with most of the yellow lights remaining incandescent. IMHO, the green lights are way too bright, esp. when the road is wet.
Now, I’ve been observing further. It makes sense that the red ones would be the first ones where I’d notice the dead LEDs, 'cause those are the ones I’m watching while stopped while I’m zipping by when the others are displaying (OK, OK, sometimes I do stop for a yellow).
But recent observations are that I’ve noticed no caution or go lights with dead LEDS, but almost every single red has at least a few.
So why would red LEDs be susceptible to failure more so than green or yellow LEDs?
FWIW when my company started putting LED brake lights on our cars the expected service life was stated at 15,000 hours. I don’t know if this would apply, but it is a similar application (off/on etc)
SanibelMan I think that you will find the main reason for the switch to LEDs is cost savings. Before LED lights the City of LA had a fleet of cherry picker trucks that worked every day. The truck would pull up to an intersections and the crew would set up and change every bulb in every stoplight at that intersection burnt out or not. Then they would move to the next intersection. LA must have thrown away 1,000s of light bulbs every day, most of which were still good.
If an LED cluster lasts 8 times as long (to pull a number straight out of my ass) then the city can reduce their bulb changing workforce to 1/8 of it previous level. That more than makes up for any difference in cost of the bulb.