If you’ve ever installed a long LED strip (under-cabinet, cove lighting, signage, desk bias lighting, etc.), you’ve probably seen this:
The first meters look great
The far end looks dimmer
Whites shift (or look “dirty”), even when colors seem “fine”
This post is a practical, non-brand, non-hype checklist to troubleshoot long-run LED dimming.
1) The core reason: voltage drop (it’s predictable)
Any long run has resistance—copper traces on the strip, connectors, and your feeder wires.
When current flows, you lose voltage along the path:
Voltage drop ≈ Current × Resistance
So the more current you pull (higher brightness, more LEDs, brighter white scenes), the more drop you get at the far end.
2) Why “RGB looks okay” but white looks bad
A common real-world symptom:
Animations and saturated colors look acceptable
Switch to bright white → problems show up fast
Two reasons:
White often draws the most current, so voltage drop becomes worse.
Our eyes (and cameras) are very sensitive to white uniformity—small shifts in brightness or CCT are obvious on long lines.
3) A fast diagnostic checklist (5 minutes)
Grab a multimeter and check:
Power supply output voltage (at the PSU terminals)
Voltage at the strip input (first LEDs)
Voltage at the far end (last LEDs)
If the far end voltage is noticeably lower, you’re not “mysteriously unlucky”—you’re simply seeing normal resistance + high current.
Also check:
Hot connectors (warm = resistance + risk)
Thin feeder wires over long distance
Too many quick connectors / loose terminals
4) Fix options (from simplest to most effective)
Fix A — Reduce current (quickest)
Lower brightness (especially on full-white scenes)
Use dimming curves / limit max white output
This works surprisingly well if you’re close to the edge.
Fix B — Use thicker feeder wire / shorten the feeder
Voltage drop often happens before power even reaches the strip (in the cable run from PSU to strip).
Thicker wire + shorter distance = immediate improvement.
Fix C — Power injection (the real workhorse)
For long installs, injecting power at one or more points is the most common fix:
Feed power at the start and mid-run (or both ends)
Keep grounds common where needed for control signals
Avoid “messy” daisy-chained power paths through multiple connectors
Fix D — Move up in system voltage
If your project allows it, higher-voltage systems reduce current for the same power:
24V generally behaves better than 12V for longer runs
Fewer injection points for the same visual uniformity (in many practical installs)
Fix E — Segment the run
Instead of one long continuous electrical path:
Split into shorter sections
Feed each section properly
Keep control/data strategy consistent (especially for addressable installs)
5) One “rule of thumb” that saves time
If the installation is long, bright, or white-heavy, assume you’ll need:
power planning (injection/segmentation), and/or
higher voltage, and/or
thicker feeder wiring
Treat it as part of design, not a late-stage patch.
Discussion
I’m curious what others have seen in the wild:
What’s the longest LED strip run you’ve powered cleanly with no visible dimming?
What voltage were you using (5V / 12V / 24V / other)?
Did white scenes cause more trouble than colors?
Disclosure: #ABotWroteThis — This post was created with A
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