If you have ever built an LED strip project that looks great in colorful effects, then immediately looks uneven on white, you are seeing a very normal electrical issue: white scenes pull more current, and current makes every bit of resistance matter.
This post is about standard constant voltage strips (not individually addressable): the common 12V or 24V RGB and RGBW types.
The one sentence root cause
Resistance × current = voltage drop.
More current means more drop in copper traces, wires, and connectors, so the far end gets less voltage and looks dim or slightly tinted.
Wiring basics for standard RGB and RGBW strips
RGB (constant voltage)
You need a constant voltage power supply and an RGB PWM controller.
Typical terminals look like:
Controller input: V+ and V- (GND)
Controller output: V+, R, G, B
Strip pads: +12V or +24V, R, G, B
Connect:
Power supply V+ → controller V+
Power supply V- → controller V-
Controller V+ R G B → strip V+ R G B (match labels)
RGBW (constant voltage)
Same idea, with one extra channel:
Controller output: V+ R G B W
Strip pads: V+ R G B W
Connect labels one to one.
Why 24V is usually easier than 12V
For the same brightness, 24V usually draws less current than 12V. Less current means:
less loss in wires and copper traces
less connector heating
more even brightness on longer runs
12V still works great on shorter layouts, but it is more sensitive to wiring and connection quality once runs get longer or brighter.
A tiny voltage drop helper (JavaScript)
This is a simple estimate for the drop in your feeder wire. It does not model strip copper perfectly, but it helps you sanity check wire gauge and distance.
// Rough copper wire resistance at 20C (ohms per meter), one conductor
// Values are approximate and vary by standard and supplier
const ohmsPerMeter = {
22: 0.053,
20: 0.033,
18: 0.021,
16: 0.013,
14: 0.0083,
12: 0.0052
};
// Estimate feeder wire voltage drop (round trip: + and -)
// lengthM = one way length from PSU to strip feed point
function feederDropV({ currentA, lengthM, awg }) {
const r = ohmsPerMeter[awg];
if (!r) throw new Error("Unsupported AWG in table");
const roundTripR = r * lengthM * 2;
return currentA * roundTripR;
}
// Example: 5A over 5m one way using AWG18
console.log(feederDropV({ currentA: 5, lengthM: 5, awg: 18 }).toFixed(2), "V");
Rule of thumb for cleaner results:
keep feeder drop under about 0.3V to 0.5V for strict installs
if the drop is bigger, use thicker wire, shorter feeders, or more feed points
The easiest fixes that work in real installs
Use power headroom
Do not size the power supply right at the limit. Leave margin so dimming and full white stay stable.
Avoid pushing all current through one end
For long runs, feed power in parallel at multiple points or from both ends.
Treat connectors as a risk
Loose or small connectors add resistance and heat. Fewer connections and better terminations usually beat “more accessories”.
Test white at full brightness before final mounting
White is the stress test. If it looks even on white, colors will usually be fine too.
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