Powering up an LED
ledcalc.com ; A useful tool to determine the value of resistors to be used in the circuit.
V = I × R (Ohm’s law)
supply voltage = 5V
resistor used = 2 x 33ohm resistor connected in parallel = 16.5 ohm
to determine current ; I = V / R
5 / 16.5 = 300mA
(Power supply voltage − LED voltage) / current (in amps) = desired resistor value (in ohms)
To calculate the amount of power that the resistor will dissipate;
Power Rule: P = (I × V ) W
If a current I flows through through a given element in your circuit, losing voltage V in the process, then the power dissipated by that circuit element is the product of that current and voltage: P = I × V.