That completely depends on what else is running on the electrical system (big speakers, CB radio, HAM radio, winch, refrigerator, hot tub, rice cooker....)
It also depends on what sort of electrical system you have. Stock (crappy battery), or have you upgraded it? Stock alternator, or have you upgraded that? How old is your battery? How much abuse has it suffered through?
It also depends on what sort of lights you want to add. Are we talking 20 watt, 55 watt, or 110 watt bulbs? HID lights will only use half to 1/3 of what a halogen light will use....and LED lights use even less.
As long as you have a good quality battery and there is nothing wrong with your charging system, you are probably fine to add 3 or 5 "ordinary" off-road lights to a JK. Just don't complain when people start making fun of you for having a light bar.