That alternator's responsibility is simply to keep the battery charged, nothing more. It doesn't use a damn bit more or less horsepower regardless if the lights are on or off. It doesn't run anything electrical whatsoever, and it's voltage is regulated by the voltage regulator. Again, try to run an automobile on the alternator alone, without a battery.
Look it up Mr. Supermechanic.
ETA; SOME vehicles will run on the alternator alone once started, but will cause electrical surges that can literally destroy most vehicle's electrical systems.
I don't have to look it up, fool.
All the electricity used by the car provided by the alternator.
The Battery provides starting power.
Try driving at night with a bad alternator and see how long until yoir battety dies, retard.
An average alternator draws 3-5 horsepower from the engine
What a fucking idiot.