All the calculators in step 2 are just doing some simple math that you can do at home: The formula to calculate resistance in a circuit is: R=V/I or, more relevant to what we're doing: (Source Volts - LED Volts) / (Current / 1000) = Resistance * So if we have a 12v battery powering a 3.5V 25mA LED our formula becomes: (12 - 3.5) / (25 / 1000 So by putting the 150 ohm resistor in there there will be a maximum current of 20 mA through the LED. Let's also say that we want the LED current to go down to 1 mA. Unless the pot has a super high resistance, it won't go down to 0 mA, and 1 mA seems like a reasonable lower limit. To make that work, our pot needs to be about 2K Ohms. A better way is to control the current through the LED or diode to be what you want. A very simple way to do this is to use a resistor. Regarding your part c, connecting three 2V 2 V LEDs in series to a 12V 12 V supply. The purpose of the resistor in that circuit is to limit the current, not the voltage. Testing an LED. Never connect an LED directly to a battery or power supply because the LED is likely to be destroyed by excessive current passing through it.. LEDs must have a resistor in series to limit the current to a safe value, for testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less. Remember to connect the LED the correct way round. oLzpvD6.

do 12v leds need resistors