Size series resistors for LED strings and arrays, including power rating.
Putting more LEDs in series reduces the voltage wasted in the resistor and raises efficiency. Individual resistors per string are needed because LED forward voltages differ enough that a shared resistor would leave current badly unbalanced. Maximising LEDs per string is the single most effective way to improve resistor-driven LED efficiency, which is why 24 V strips use six-LED groups.
LED Series Resistor
R per string = (V_supply − n V_f) ÷ I_string; efficiency = LED power ÷ total power
R per string = (V_supply − n V_f) ÷ I_string; efficiency = LED power ÷ total power Putting more LEDs in series reduces the voltage wasted in the resistor and raises efficiency. Individual resistors per string are needed because LED forward voltages differ enough that a shared resistor would leave current badly unbalanced.
Maximising LEDs per string is the single most effective way to improve resistor-driven LED efficiency, which is why 24 V strips use six-LED groups.
This calculator takes 5 inputs: Supply voltage, Forward voltage per LED, LEDs per series string, Parallel strings, Current per string. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.