If you are growing indoors and are only growing a few plants, a dozen or so, maybe up to 25, the odds of being caught are pretty low. As long as you're not being obvious about it, it's unlikely the law will catch up with you. A 400watt metal halide fixture draws less power than a 1500watt space heater and will most likely not draw any attention. Just make sure there is no light leaking out or any smell from the budding babies and you should be ok. On the other hand, if you're planning on growing for profit and suddenly crank up a dozen or so 1000watt metal halides, it's very likely the local power company will take notice and have no qualms about reporting this sudden surge in power consumption to the authorities. Or they will send a couple guys around to check for problems (such as a massive short to ground) to make sure and I think in most states they are required by law to report it.