This. Commercial PV panels are about 18% efficient at converting solar energy into electricity, and the best fluorescent bulbs are about 15% efficient at converting electricity into light (the rest becomes heat). So if you install PV panels to power your lights, you're only converting about 2.7% of the sunlight hitting your solar panels into interior light.
Fluorescent lights are around 80% efficient (similar to LEDs). Incandescent lights (traditional light bulbs) are around 15% efficient. It's why you can replace a 60W light bulb with a 13W CFL.
Uh, no. An incandescent bulb is 3-4% efficient, 5% efficient at best (that is 5% of the energy is emitted as visible light, 95% is emitted as heat). Fluorescent bulbs and LEDs are far more efficient, but nowhere near even 50%. Fluorescent bulbs are around 4x as efficient, LEDs around 6x.
Using direct lighting instead of PV + electric light is a huge win, and leaves the rest of the roof open for PV installation if you want.
To give an idea of how much lighting is used, I counted the lights in a Hobby Lobby last time I was there (what else would a guy do in there?) and they had about 3000 40W fluorescent lamps. That's 120KW just for lighting (most of which turns into heat that the A/C has to pump out, by the way) which works out to about $12/hour here in TN. Walmarts don't light as brightly as a Hobby Lobby, but they have larger stores. The energy savings from the skylights is really big.