Ever finished an under-cabinet or tape light installation only to notice the lights at the far end are dimmer or a different color than the start? This isn't a faulty product—it’s voltage drop. For indoor projects using DC LED drivers, mastering this is the key to professional-grade results. If you are just starting your project, check out our Ultimate Guide to Buying LED Strip Lights.
What is Voltage Drop?
Voltage drop is the gradual decrease in electrical potential as current travels through a circuit. In LED strip light systems, this happens for two specific reasons:
- Internal Resistance: The flexible copper traces on LED tape are extremely thin, creating resistance within the product itself as the current travels down the line.
- External Resistance: The "home run" wire traveling from your DC driver to the start of your lights also consumes voltage before it even reaches the fixture.
Why Voltage Drop Hits LED Strips Harder
Unlike standard fixtures, LED strips are uniquely sensitive to voltage fluctuations. The "dim end" effect causes specific issues for indoor lighting:
- The Color Shift Phenomenon: In indoor tape lights, voltage drop doesn't just cause dimming. Because different LED colors (Red vs. Blue/Green) require different voltages to operate, a drop can cause an RGB strip to turn pinkish at the end. Similarly, a high-CRI white strip might shift toward a yellow or amber hue at the far end of the run.
- Sensitivity of COB Strips: Modern COB LED strip lights feature a high density of chips to create a seamless "dot-free" look. While aesthetically superior, this high density makes them more sensitive to voltage loss, making proper power management critical for maintaining that seamless effect.
The Three Variables of Resistance
- Wire Gauge (AWG): Thicker wire (lower AWG) has less resistance and carries current more efficiently over distance.
- Run Length: The further electricity travels from the power supply, the more resistance it faces.
- Load (Wattage): High-wattage strips experience drop faster than low-wattage accent strips because they pull more current.
Voltage Drop & Wire Length Reference Charts
Use these tables to select the correct wire gauge for your installation. For most professional applications, a maximum drop of 3% is the industry standard to maintain uniform brightness and color accuracy.
12V Voltage Drop Chart
| Load (Wattage) | 18 AWG | 16 AWG | 14 AWG | 12 AWG | 10 AWG |
| 5W (0.42A) | 65 ft. | 100 ft. | 160 ft. | 240 ft. | 392 ft. |
| 20W (1.67A) | 16 ft. | 25 ft. | 39 ft. | 59 ft. | 98 ft. |
| 40W (3.33A) | 8 ft. | 12 ft. | 20 ft. | 30 ft. | 49 ft. |
| 60W (5A) | 5 ft. | 8 ft. | 13 ft. | 20 ft. | 32 ft. |
24V Voltage Drop Chart
| Load (Wattage) | 18 AWG | 16 AWG | 14 AWG | 12 AWG | 10 AWG |
| 5W (0.21A) | 261 ft. | 401 ft. | 639 ft. | 959 ft. | 1570 ft. |
| 40W (1.67A) | 32 ft. | 50 ft. | 79 ft. | 120 ft. | 196 ft. |
| 60W (2.5A) | 21 ft. | 33 ft. | 53 ft. | 79 ft. | 130 ft. |
| 100W (4.17A) | 13 ft. | 20 ft. | 31 ft. | 47 ft. | 78 ft. |
The 24V Solution: Distance Without the Dim
The most effective way to combat voltage drop in under cabinet lighting is to choose a 24V LED tape light over a 12V system. Because 24V systems operate at half the current for the same wattage, they experience significantly less resistance. As shown in the charts above, a 24V system can run nearly twice as far as a 12V system before dimming becomes visible.
Three Pro-Fixes for Long Runs
If your layout requires long distances or multiple puck lights, use these strategies to ensure uniform light:
- Power Injection (Loop-Back): Run a second set of wires from your DC driver to the very end of the LED strip. This "injects" fresh voltage at the tail, ensuring perfectly uniform brightness and color throughout the run.
- Center-Feeding: Connect your power lead to the middle of the run rather than the beginning. This effectively cuts the electrical travel distance in half for each side of the strip.
- Upsizing "Home Run" Wire: If your 24V power supply is hidden in a remote closet, use thicker 14 AWG or 12 AWG wire to reach the cabinets. Switch to smaller tape leads only once you reach the start of the lights to minimize resistance over the long distance.
Mastering the Flow
Voltage drop is a law of physics, but it doesn't have to ruin your design. By understanding the relationship between voltage, wire gauge, and run length, you can prevent uneven brightness and color shifting. For more technical details on powering your system, see our guide on how to choose an LED power supply. Whether you choose a 24V system or implement power injection, planning for resistance ensures your LED strips perform at their peak.
