There are two basic voltages for LED strings, 5Vdc and 12Vdc, which one is better to use. Well that depends.
Let me explain a little bit about how LED’s work. The brightness of a LED is dependent upon how much current flows through the LED. So the voltage used to drive the LED does not really matter, it is the current. Nominally, most LED’s have a forward voltage of 2 to 3 Vdc. This means that you need to have a drive voltage greater than a the 2-3 volts, so both 5/12 Vdc will both work. But if you know that power is voltage times current it is clear the 5Vdc power is more power efficient.
Another interesting aspect of LED’s is that to the human eye, full current in the LED to half current brightness is barely discernible. But as you get near the bottom of the dimming curve our eyes are very sensitive and can see the small changes in brightness (for 8 bit lights or less). Most 12Vdc strings are driven at about the same current as the 5V strings, so it will take a twice the power, however this is worth the ability to use smaller gauge wire and not inject power.
There are now some 12V strings that place a 5V power supply integrated circuit with each of the controller chips. These strings have very good uniformity of brightness, since each of the pixels are driven at a regulated 5Vdc. With the voltage converters built into the 12V strings, I really can’t recommend the 5V strings. The need to inject power and issues with voltage drop do not make them a viable option. The two basic types of strings with regulators built in are the Technicolor and the Ink series.