A friend of mine did something similar. He put in a small solar array with only 3 panels, an inverter/charger, and 400 Ah of 12-volt batteries. This DC then feeds into a breaker panel and goes to lights in all the rooms. He uses LED spotlights, the little bulbs that plug into wires stretched across the ceiling. He said he just ran 10-gauge Romex wires through the attic, down to DC-rated switches and then to the ends of the cables.

He still has all the original 110 wiring and fixtures in the house, but this battery-backed solar system runs all his lights. It can easily go 2 days without sun before he needs to use the regular lights. Another benefit is that DC LED bulbs are by definition flicker-free, and also low consumption (4-6 watts each) but bright. He calculated he can light each room better than before with 6-8 bulbs, so 40-50 watts, thus only 4-5 Amps (@ 12 VDC) to each room.

All the big appliances in the house still run off of of AC, but he does have a 110 inverter so that he could run a critical appliance such as a fridge during an extended outage.

So this little system replaces 1-2 kWh of incandescent lighting per day (CFC or LEDs on 110 would be less, but not flicker-free), while providing lights during outages. He says it's not cost-effective (the usage displaced by solar and battery usage doesn't cover the cost of the system), but the backup powers is worth it to him.