When using multiple LEDs from the same power source - series, parallel or individual wiring with a resistor per LED?
I'm just curious about how they do it with car lighting which uses many LEDs per lamp unit. There would be disadvantages with series or parallel wiring with shared resistors if LEDs failed, but they tend to have a pretty long life?
I've not looked at any car ones, but in the non-car ones usually multiple serial chains. It's quite common to see one chain has died, resulting in a cluster of dead LEDs, and I've seen that on cars too, so it's probably the same. Supply ballast can be a constant current source rather than just a crude resistor.
They have been in use on the rear of busses for some time, but failures appear to be randomly placed rather than in strips.
I thought this new solid state technology was supposed to be much more reliable but these LED rear lamps don't seem anymore reliable than the filament types they are replacing. They don't all fail at once, but they don't give the impression that overall life is better, as presumably once a failure occurs the unit must be replaced.
Roger R
That makes sense.
Strange. My experience is the opposite - all the London buses with LED rear lights seem to be fine. Very different from when they were filament types. Although the buses are much newer these days too.
I dunno if they can be easily repaired. No reason why not. LEDs used as signalling devices seem to last forever - but up the brightness and the life suffers.
Series with a resistor as close to supply rail as poss, i.e. 3 white plus resistor on 12V. Parallel series chains. Paralelling diodes with no resistor allows some diodes to become current hogs and glow brighter than rest.
Adam
Parallel series strings is generally the way to go. How high a voltage your strings should add up to depends on how stable the V_supply is.
LED life depends on current. At the low currents of LED indicators, they tend to last a life time. But once you push them hard to get useful lighting output, lifetime drops massively.
NT
I think I know what you mean to say, but what you have written comes out as "They last until they fail, which is sooner if you push them."
I guess "life time" = user, "lifetime" = LED?
Chris
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