A constant-voltage strip fed from one end always runs dimmer at the far end. The copper in the strip and the supply wire has resistance, current flows through that resistance, and Ohm’s law converts it into a voltage that never reaches the last LED. The fix is arithmetic, not guesswork: calculate the drop, then choose the feed pattern and wire gauge that keep it inside the range where the strip still meets its rated output.
The Drop Math
Voltage drop equals current times resistance, and resistance comes from the wire table. For copper at room temperature:
| Conductor | Resistance per meter (one way) | Drop over 10m round trip at 5A |
|---|---|---|
| AWG 18 | 0.021 ohm | 2.1V |
| AWG 16 | 0.013 ohm | 1.3V |
| AWG 14 | 0.0083 ohm | 0.83V |
The round trip matters: current flows out through one conductor and back through the other, so a 5 meter run of wire contributes 10 meters of resistance. A 24V strip drawing 5A at the end of a 5m AWG 18 extension loses about 2.1V, which is 8.8 percent of supply. The last meter of strip sees less voltage, and phosphor-converted white at lower voltage draws lower current, so the tail visibly dims.
Why 24V Strips Feed Longer
The same strip at 12V draws twice the current for the same power, and drop is proportional to current. Halving the supply voltage doubles the drop percentage: a run that is acceptable at 24V is roughly four times worse in relative terms at 12V. This is why the practical feed-length rule of thumb reads about 5 meters per feed for a 24V strip and about 2.5 meters for a 12V strip, before any wire extension adds its own loss.
Feed Patterns That Even Out a Run
- End feed is the default and the worst case; the whole strip length feeds through one point.
- Center feed splits the run in two, so the worst path is half the length and the drop falls by about a factor of four.
- Double end feed (power to both ends) halves the effective resistance again and usually evens a 10 meter run enough to pass visual inspection.
- For runs beyond 10 meters, insert a driver or amplifier at each segment rather than stretching one feed.
Strip copper itself has resistance too, and the printed bus width sets it. A dense 14.4W per meter strip carries more current per meter than a 9.6W one, so the same physical length hits the drop wall sooner; the wire table above only covers the extension, not the strip bus.
Where the Driver Goes
Place the constant-voltage driver close to the strip start and run mains to the driver, not low-voltage across the building. A driver 15 meters from the strip needs a thick low-voltage cable to hold the same drop budget; a driver 15 meters from the panel just needs ordinary mains wiring. Mount the driver where convection works and read its derating curve: a 100W driver in a closed housing above 40C ambient may be rated closer to 80W, and an underrated driver is the second most common cause of a dim, warm strip run.
FAQ
How much voltage drop is acceptable on a strip? Keep total drop under about 5 percent of nominal; beyond that the tail loses both output and CCT accuracy on white strips.
Does a higher-wattage driver fix the dim tail? No. Drop is a resistance problem in the path, not a supply capacity problem; only feed pattern, wire gauge or segment amplifiers change it.
Related reading
- DALI, 0-10V and PWM dimming protocols compared for fixture control
- more fixture selection answers in Lighting Q&A
