Why LED street lamp can parallel LED without damage?


Here's an excerpt from some Yuji LED datasheet:

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So yes, if you order in quantity you can get LEDs with good Vf match. Wiring them in series strings means the Vf mismatches add and substract which increases the probability that total Vf will be closer to (number of LEDs x average Vf).

If they are mounted on an aluminium PCB which keeps them all at the same temperature, Vf under load will track pretty well. This means they can be arranged in series/parallel strings without resistors or other current sharing/limiting devices. This is very common in LED lights.

If the LEDs are not binned by Vf, and especially if they are at different temperatures, then it wouldn't be a good idea to parallel them.

You should not parallel leds, when you do not take the time to ensure they match in forward voltage drop, current draw and temperature curves, or more. The advice to not parallel leds is an often regurgitated statement without critical thinking. Like anything else, if you look into the reasons behind it and the math and practical application you know its just more complicated.

Parallel leds are used in multiple applications and its not a problem when you match the leds. Commercial products like the street lamp are one of those applications.

An incoming or source-inspection process could match the LEDs reasonably well. Still, there's probably a low-ish resistor on each series string to compensate for any residual string-to-string Vf difference that may come up.