24V vs 12V Outdoor LED Power: The Voltage Drop Math

24 V is not automatically the better choice. Below about 3 metres and 30 W per run, 12 V modules cost less and you gain nothing from 24 V. The math below tells you exactly where the crossover sits — and it is further out than most specifiers assume.

The Formula

Voltage drop on a two-wire run:

Where L is one-way length in metres, I is current in amps, and R is the conductor resistance in Ω/m. The factor of 2 accounts for the return path.

Copper resistance at 20°C:

Note that resistance rises about 0.4% per °C — a cable inside a hot sign cabinet at 60°C carries roughly 16% more resistance than the table value.

Worked Example: 5 Metres, 60 W

On 12 V: I = 60 W ÷ 12 V = 5.0 A ΔV = 2 × 5 m × 5.0 A × 0.0132 = 0.66 V → 5.5% of 12 V

Acceptable. Now push to 10 m: ΔV = 2 × 10 × 5.0 × 0.0132 = 1.32 V → 11%. Visible dimming at the far end.

On 24 V: I = 60 W ÷ 24 V = 2.5 A At 10 m: ΔV = 2 × 10 × 2.5 × 0.0132 = 0.66 V → 2.75% of 24 V

Same drop in absolute volts, one quarter the percentage, because the denominator doubled and the current halved. That is the entire argument for 24 V, and it is why drop scales with the square of the voltage ratio when you hold power constant.

The Crossover Distance

Hold power and acceptable drop constant at 5%:

So the practical rule: under 3 m, 12 V. Over 5 m, 24 V. In between, decide on cost.

Why Uniformity Matters More Than Brightness

Here is the failure mode that costs you the job. A 10 m run at 11% drop does not look “11% dimmer.” It looks like two different products installed side by side, because the near end is at full voltage and the far end is not.

Human brightness perception is roughly logarithmic, but in dark-adapted conditions — which is exactly when signage is viewed — a 15% luminous difference between adjacent sections is clearly visible. Customers do not report “voltage drop.” They report “your LEDs are inconsistent,” and it reads as a quality defect even though every module is functioning correctly.

Undersized cable is the most common cause of this, and it is the cheapest thing to fix at design stage.

Where Each Voltage Wins

Choose 12 V when:

• Runs under 3 m
• Module density is high and cut points are frequent (12 V strips commonly cut every 3 LEDs vs 6 on 24 V — shorter cut intervals mean less waste on complex shapes)
• The design uses many short branches from one driver

Choose 24 V when:

• Runs over 5 m
• Cable cost matters — you can often drop one AWG size, which on a 200 m install saves more than the voltage decision costs
• One driver feeds a long perimeter

Two Traps

1. Mixing voltages on one driver. Obvious, but it happens on site when a replacement reel is the wrong voltage and “it’s only a bit brighter.”
2. Feeding from one end only. On any run over 5 m, feed from both ends or from the centre. This halves the effective length in the formula and is free.

For load sizing before you pick voltage, see the signage load calculator worksheet. For the 200 W unit available in both voltages, see R-200-xx and the 60 W unit for short runs.

Send us your run lengths and module count — we will tell you which voltage and which cable gauge, with the drop figure for each leg. → Request a quote