Indeed you do use 35W whether it's 12V, 120V or 1200V. But the efficiency (lumens/watt) may be different - typically 15% more efficient in low voltage applications. That's what matters. Low voltage 12V stuff frequently has a good efficiency...but the transmission difference really matters. You need some heavy duty cable to send 12V any kind of distance.
Having said all that, you'll probably get more lm/W from fluorescents. That's assuming, of course, that you don't care about colour rendering, can't see the flicker* and don't mind if they look kind of ugly.
LED might be interesting, but probably not *quite* ready yet for prime time. Soon, though.
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