Originally Posted by CRAZYHAWK
Being the car wasn't running, you ran the lights with 12 volts. You'll have around 14 volts with car running.
Power = (E x E)/R , that's voltage squared divided by resistance
You'll have 36% more power with the car running.
I did have my car running for both tests. I wanted to make it real life test. I turned it off to takes the shots.