[AT] OT LED question

[Steve W.]

Dan Glass wrote:
> I was driving through town today and noticed that some of the traffic 
> lights that have been switched to LED's were about 1/3 to 1/2 burned 
> out.   I don't know what they switched from but I never remember seeing 
> one of them burned out.  They had about 50 or so LED in each red or 
> green light and of those 50 about 20 or 30 random LED were out.
> 
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That is because of the way LEDs are connected internally. They create a 
pattern to connect the LEDs in series and parallel. Then they spread out 
the groups so that the sections that fail are not grouped together. That 
is how you get the "random" failure pattern. Instead of one corner of 
the lamp failing and possibly appearing as an arrow or other symbol they 
make it random so that people who are color blind cannot misinterpret 
the image.

I have actually seen very few LEDs made in the past few years actually 
fail. Most of the time it's in the driver circuits or a lack of enough 
heat sink to pull the heat from the actual LED chip that kills them.

-- 
Steve W.