\[R_s=\frac{V_s-V_f}{I_{LED}}\]
Variables
Rsseries resistor (Ω)
Vssource voltage (V)
VfLED forward voltage (V)
IledLED current (A)
Description
What is this formula?
The LED Series Resistor formula calculates the resistor value needed to safely operate an LED from a voltage source. The resistor limits the current flowing through the LED and prevents damage.
When to use it
Use this formula when designing LED circuits powered by batteries, power supplies, microcontrollers, or electronic driver circuits.
Example
A red LED with a forward voltage of 2 V operates from a 9 V battery at a desired current of 20 mA.
Given:
Vs = 9 V
Vf = 2 V
Iled = 0.02 A
Formula:
Rs = (Vs - Vf) / Iled
Substitution:
Rs = (9 - 2) / 0.02
Result:
Rs = 350 Ω
A resistor of approximately 350 Ω is required.
Applications
LED indicators, electronic displays, Arduino projects, lighting circuits, embedded electronics, and educational electronics projects.