Friends, its always good to connect LEDs in parellel instead of series, because nowadays LEDs are not in good quality, and will totally goes off if any of the LED fuses. so its easy to connect an LED with a 470 Ohms half watt resistor, on 6 volts, and 1 Kilo Ohms at 12 volts. a simple transistorised ( 8050, or 8550) circuit will give you an option for intensity control of the light.