To calculate the resistor value for an LED in series with a resistor, you can use Ohm’s Law and the LED forward voltage and current specifications.

Identify the supply voltage (Vs): This is the voltage of the power source (e.g., 5V, 12V).

Forward voltage of the LED (Vf): This is the voltage drop across the LED when it is forward-biased. You can find this value in the LED’s datasheet. Common values are around 2V for red LEDs and up to 3.5V for blue or white LEDs.

Forward current of the LED (If): This is the current at which the LED operates optimally. This value is also found in the LED’s datasheet, typically around 10-20mA (0.01-0.02A) for standard LEDs.

Calculate the resistor value (R) using Ohm’s Law:

𝑅 =𝑉𝑠−𝑉𝑓 / 𝐼𝑓

Power Rating of the Resistor: Ensure the resistor can handle the power dissipation. The power dissipated by the resistor can be calculated using:

𝑃=𝐼𝑓^2×𝑅