If a resistor in each series is connected again, the resistor should be stepped down (divided) 12V-4 = 8 (V). According to the ohm rating R=V/A=8/0.02=400 ohms, the current flowing through the resistor is 20mA=0.02A, because the actual power consumption of the power supply is1a. Therefore, a resistor with a nominal value of 430 ohms can have a resistance power W=VA=8(0.02)=0. 16 watts, and 0.25 watts can be selected according to the actual production series of resistance power.

It is also possible to connect two LEDs in series and then connect a resistor in series. At this time, the partial voltage of the resistor is calculated as 4V, and the resistance can be selected as 0. 125W 220Ohm, which is more energy-saving.

If three LEDs are connected in series without series resistance, the direct 12V power supply will easily damage the LED overcurrent.

Resistors with the same resistance can replace those with low power, and those with low power cannot replace those with high performance.