milktea: The conservation of mass comes into play here; if you have ~50w worth of CFLs pumping light into your room, then the most electricity the solar cells could absorb is 50w, but realistically, efficiency will be more like 20% for the solar cells, and ~20% efficiency from the light bulbs(and 80% of 50w lost as heat), and the solar cells won't form a black hole that sucks in all of the light from the room, so you can assume at most they'll absorb ~1% of the light.
So, you'll get 50w * 20% = 10w of light, * 1% absorbed = .1w * 20% solar cell efficiency = .02w of continuous power from indoor lighting, as to say: You'd be better off plugging it in.