[antonkochubey]

If you supply ground from one end, and +24V (or whatever) from the other end, brightness will be equal throughout the strip :)

But it would also be a good idea to measure voltage drop when it's powered on, and compensate accordingly, if your PSU allows for it.

[eemil]

What a brilliant, simple solution. This way each segment in the LED strip has an equally long current path, and should have identical voltage/brightness.

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That being said, 20-50m is a really long run even with 24V LEDs. Even using this trick, you'll run into significant voltage drop and heat in the LED strip's copper traces since they're only so thick. There's a reason why manufacturers specify a maximum length. I would check the datasheet and split the strip into multiple segments depending on this value. Maybe there are some LED strips designed for this use-case, with an even higher voltage and/or thicker traces.

[windexh8er]

Edge injection works extremely well, but still has distance limitations. You're not going past 20m per segment of power with something like WS2811s. There's no way to do 50m without power injection within the segment, even with 24v strips. That is unless they're not RGB or low density.