“Voltage drop” means the gradual diminishing of voltage along the length of the wire as electricity travels away from a power source. The term applies to what happens when a light or appliance is at a great distance from the power source. Think of a charged electrical wire as a pipe and the electricity as water. If the water pressure is constant, the pipe is fullest and the most pressurized at the source of the water, and gradually tapers off as the pipe gets longer. So with electricity, if the voltage is 12V at the power source, it gradually drops the farther you get from the power. So 50 feet from the power source, the actual voltage might be 10.5V.
When installing LEDs at distances greater than about 40 feet from the power source, we recommend that customers consult a voltage drop calculator (such as the one at www.nooutage.com or at CSG Network), and consider using a heavier gauge wire than the 18 gauge that is standard for 12V DC power. (Using a heavier wire, like increasing the size of a water pipe, allows more current to travel farther.)
Keep in mind that we don’t recommend running our 12V LED lights at a voltage greater or less than 12V DC, as it greatly shortens the life of the light, even though it may be possible to operate 12V LEDs with as little as 10V of power.