If I understand all of your scenarios, I would vote for #2. I wouldn't get more than a meter from the window, however. I grow my orchids inside close to a south-facing window and it has worked well. The light does change with the seasons -- so you may have to experiment a little to get it just right. I have found that eastern light doesn't last long enough during the day (at least in my house, the starts to get shady by mid-day). Western sun is too hot and northern sun is never enough. The radiator might make things too dry, so you will have to keep the humidity up, but it sounds like you are already doing that.
Honestly, I don't count the lights that my plants get from lamps, overhead lighting etc. If they aren't grow lights or the plants are inches from the flourescent tubes, it really isn't doing them all that much good.
Since your plant has been "in the dark" for awhile, I'd move it toward the light gradually. If you move it to a south-facing window all at once, it could get burned.
Lastly, you mentioned growing it in a huge glass container with pebbles -- if it is standing in the water, you might have root problems.
Really, a photo of your set up would be very helpful.