24 V or 12 V LED Strip: Why Run Length Decides It

The visible symptom of getting this wrong is simple: the far end of the run is dimmer than the near end. It is usually not noticed during installation, because installers look at the strip from a metre away with the room lights on. It is very noticeable at handover, at night, from across the room.

What voltage drop is

Current flowing through the copper tracks on the strip encounters resistance. Resistance converts some of the voltage into heat along the way. By the time current reaches the last LED, less voltage arrives than left the driver.

LEDs are sensitive to this. A modest drop in supply voltage produces a visible drop in light output, and often a slight shift in colour.

Two things determine how much drop you get: how much current is flowing, and how far it has to travel.

Why 24 V goes further

For a given power per metre, a 24 V strip draws half the current of a 12 V strip. Power is voltage times current, so doubling the voltage halves the current for the same power.

Voltage drop across a fixed resistance is proportional to current. Half the current means half the voltage lost per metre.

The advantage is larger than that, because what matters is not the absolute voltage lost — it is the loss as a proportion of the supply. Losing 1 volt from a 12 V supply is an 8.3% drop. Losing 1 volt from a 24 V supply is a 4.2% drop.

Combine both effects and a 24 V strip typically runs three to four times further than a 12 V strip of the same power before reaching the same visible dimming.

Practical maximum run lengths

Maximum run length depends on power per metre. Higher power means more current, which means more drop per metre. Actual limits depend on the copper weight in the specific strip, the acceptable drop for the application, and whether the run is fed from one end or both.

The general principle: the higher the power per metre, the shorter the run before you need another feed.

Three ways to fix a long run

Feed from both ends. Take the supply to both ends instead of one. This roughly halves the effective distance current travels and is usually the cheapest fix — one extra cable, no extra hardware.

Split into sections. Break a long run into shorter sections, each with its own feed. All sections can still run from the same driver provided it has capacity.

Increase the feed cable size. Helps with drop in the cable from driver to strip, but does nothing about drop along the strip itself. Useful when the driver is far away, not useful for a long strip.

What does not work: raising driver voltage to compensate. Over-driving the near end to fix the far end shortens LED life at the near end and produces a visible colour difference along the run.

Where the driver goes

Voltage drop happens in the driver cable too, and that cable is often longer than people assume — the driver ends up in an accessible ceiling void near a maintenance hatch, which may be twenty metres from the fitting.

If a long driver cable is unavoidable, size the cable for the run. It is cheaper to specify heavier cable at design stage than to diagnose a dim run after the ceiling is closed.

Constant voltage, not constant current

All three products are constant voltage, 24 V DC. Any constant voltage 24 V driver of adequate rating will work.

Size the driver with headroom. Total strip load plus at least 20% is a reasonable margin. A driver running permanently at its rated maximum runs hot, and heat is the primary cause of driver failure.

We do not supply drivers. Most contractors and M&E consultants have a preferred brand and dimming protocol, and that decision belongs with the electrical design.

Checking a run at design stage

Two questions answer most of it: how long is the longest continuous run, and how much power per metre does the design need?

If the run is long and the load is high, plan for a feed at both ends or a mid-point feed before the drawing is issued. Adding a feed on paper costs nothing. Adding one after the cove is closed costs a day.