I just want to say I am no great expert first! But I do understand about having limited window space (and limited wattage availability on my "grow room"'s circuits) and having to grow pretty much everything under lights.
If wattage is one of your limitting factors, then LED grow lights might be your answer, but you'd have to choose them very carefully. Ray here sells some of the good ones
Orchid Growing Supplies Semi-hydroponics Hydroponics Orchid Books PrimeAgra and has some nice t5 lights too, which you might be interested in.
LED lights last for a long time too. I am currently buying and trying different kinds of LED light arrays to see which fits my limited space, since I can't plug in another 400 watt MH lights in here without tripping the circuit breaker!
I also tested some halogen lights with my light meter in a store and the amount of light given off was great, but then so was the heat generated which is a no-no for me, since the MH light brings the room temperature up 5 degrees already.
The advantage of the LEDs aside from low electricity cost is that a lot of them, inluding Ray's, screw in standard e26 Edison fixtures. You'd need something else for the halogens but it shouldn't be too expensive. Those 2 choices and CFL are pretty much the only things that match "low-watt" as a criteria to my knowledge
As for a non obstrusive setup, I can't think of much of anythng except a hanging lamp with a standard socket with a flood LED bulb (like these
E27 93 SMD1210 3528 6W Led 380Lumen 6500K Light Bulb Lamp 110V | eBay) or you could keep going with the spotlights if they currently work for you. I've just ordered 2 of the bulbs I just link to try them out, so I can't confirm their effectiveness yet but they should work out.
Hope this helps and that someone with more lighting experience pops in too