I'd recommend using an online LED calculator(http://ledcalculator.net/) to work out what resistors you'll need to keep the current down to within what an LED can operate on. I'd also recommend not having every LED in series as if one burns out the entire circuit will fail.I want to make an LED bulb which plugs into mains supply. I use a diode which clips off one half of power supply and delivers the positive half to the array of bulb connected in series. Since the mains at my house is 220 volts the voltage delivered would be 220/2=110 volts of pulsed DC supply. Hence I can connect about 36 white LEDs in series. Can this work or not?