Pricing and details on the GTR Lighting Resistors: &utm_source=youtube&ut
So assuming a 12-volt power source and a white LED with the desired current of 10 mA; The formula becomes Resistor = (12-3.4)/.010 which is 860 ohms. Since this is not a standard value I would use an 820-ohm resistor. We also need to determine the power rating (watts) of the required resistor.Dimming an LED light is, add a resistors to the connection or even several resistors, to ensure you get the right brightness, this is called analog dimming. There is probably already a resistor in the line to drop the 12V, so the actual value you need is probably less than 10K. Now, we get to the tricky part: some LEDs will begin to dim
A cheapo LED will probably be happy with about 20mA. The current determines how much series resistance is required. 3) If your LED specimen happens to have a Vf of 3.2V it might not even light, or will light dimly. with a 3V supply. 4) A CR2032 can provide only a small current and has a short life-time.
Red LEDs usually have a 1.7V drop. If the LEDs are wired in series, they will drop about 5.1V. 9V - 5.1V leaves about 3.9V across the current limit resistor. I'm going to further assume that you want to have the LEDs run at 20 mA max. So: 3.9V / 0.02 Amps = 195 Ohms. The closest standard (E12) resistors are 180 or 220 Ohms. I'd choose 220 Ohms.Not just any 330 Ω resistor will work for us, we need the resistor to meet or exceed the resulting power dissipation. Note: A resistor's power is rated in watts. The formula for electrical power is P (Watts) = I (Amperage) * V (Volts) fVTF.