what is the formula for calculating the resistor i need for an led based on 120 volt half rectified mains given 'x' for led voltage and 'y' for led current draw? thank you!
Using a capacitor as a dropper dissipates less power and is a better idea, if you dont want 2 leds use a 1n4001 in place of one of the leds.
Be carefull with any circuit connected to the mains - dangerous.
As DP says, the cap is a better route. A current-limiting resistor for 120vac can be big and radiate as much power as a small incandescent lamp, making the LED pointless if you used the lamp instead!