# LED Stoplight Teardown



## PhotonWrangler (Jun 22, 2008)

I stumbled across a teardown report of a red LED stoplight here. It looks like an older unit as the recent ones I've seen use a denser array of LEDs on a printed circuit board.

Anyway, I was surprised to see how many of the LEDs are wired in series. It seems to me t hat an LED that fails open would take out a significant portion of the array in this configuration. While I've never seen an LED traffic light that had a major chunk burned out, it makes me wonder. This is a potential safety issue if a major chunk of the light goes out.

I'm hoping that modern units have their LEDs wired in parallel. Does anyone have specific knowledge of LED arrays used in modern traffic lights?


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## LukeA (Jun 22, 2008)

PhotonWrangler said:


> I stumbled across a teardown report of a red LED stoplight here. It looks like an older unit as the recent ones I've seen use a denser array of LEDs on a printed circuit board.
> 
> Anyway, I was surprised to see how many of the LEDs are wired in series. It seems to me t hat an LED that fails open would take out a significant portion of the array in this configuration. While I've never seen an LED traffic light that had a major chunk burned out, it makes me wonder. This is a potential safety issue if a major chunk of the light goes out.
> 
> I'm hoping that modern units have their LEDs wired in parallel. Does anyone have specific knowledge of LED arrays used in modern traffic lights?



Outside the mall by my house there are LED traffic lights which are losing emitters after less than a year. On the primary route through the intersection(the one that's green most of the time), a few green LEDs are out. On the secondary route the reds are taking heavy losses. I think each color must have the same number of emitters per string and at the same voltage and the reds are getting seriously overdriven.


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## Bogie (Jun 23, 2008)

Those are older units at least around here NYC is getting units without the diffusing lens I broke one down in this thread


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## bobrip (Dec 18, 2008)

Makes you wonder if the life is as good as stated. They should dim those lights at night to increase life and save energy. If they were in parallel it would cost a lot of circuitry, connections, and I suspect power. At least they are not like a regular stop light. I think they fail all at once, or do they have two bulbs
The LED is a soft failure, and you can easily detect it.


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## SemiMan (Jan 31, 2010)

Looks like cheap Chinese made junk.... no North American or European ... or Japanese... or Korean ...or...... company could afford to build a unit this way ..... and thankfully they do not.

Most traffic lights that are LEDs in places like the U.S. are using power leds behind a lens. You just don't identify them as LED always as they do not have that distinctive look.

Semiman


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## PhotonWrangler (Jan 31, 2010)

GE makes both kinds. Their new GT1 has a light distribution that highly resembles an incandescent bulb, and their older RT11 has that distinctive grid look. I don't think I've seen a GT1 in person yet. I probably would've noticed it from the crisp on/off transition.


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## Apollo Cree (Jan 31, 2010)

I've seen plenty of LED traffic signals with some strings of LED's burned out. I've never seen one with enough LED's burned out that the color of the signal wasn't clearer and brighter than the average incandescent traffic signal. I've seen plenty of incandescent traffic signals with burned out bulbs.


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