The LED strip or LED neon light is powered by constant voltage 5V/12V/24V and the current is running on the bottom trace of PCB which is typical 1 OZ thickness. The trace of PCB is with resistance that will ‘eat’ some voltage and generate heat that we could regard it as a resistor. The longer PCB or higher current, the more voltage drop is higher and to some extent, we could see obvious brightness difference from beginning to the end of LED strip that is  also the reason that that LED strip is running at maximum 5 meters when powered from 1 end in serial.

We could calculate the voltage drop on the trace under specific power and PCB width by below link:

calculate the voltage drop of the trace

There are 2 solutions for us to reduce the effect from voltage drop:

-powering the LED strip from both ends through the same power supply and controller(please note using different power supply when damage the LED strips)

-adds IC in the circuit to maintenance the current and make the brightness uniform from begin to the ends. The extended maximum length could be at least 10 meters and the small power, the longer is.

As the input cable carries the biggest current that will be voltage drop on the cable as well. Below table is the maximum cable length recommendation under different power input for DC12V LED strip:

Maxium cable length suggestion for DC12V LED Strip per carrying different power

Below table is the maximum cable length recommendation under different power input for DC24V LED strip:

Maxium cable length suggestion for DC24V LED Strip per carrying different power

When there is dimmer or controller used with the LED strip light, the cable length shall not exceed 10 meters considering the PWM signal interference and electromagnetic compatibility.