It has been my experience, in studying lamps and specifications, and experimenting with configurations. That very LOW voltage bulbs with high operating currents are kind of rare- and probably for good reason:
1. Very low voltage bulbs (like <6V) generally have poor efficiency compared with 6+V bulbs. Efficiency potential achieves "optimal" levels in bulbs ~12V+
2. designing a filament for a low-voltage high current application usually requires making a few tradeoffs. In order to get a lot of current to flow across it, it has to be shorter and thicker. Thicker filaments of short length will have less exposed and unobstructed surface area, and therefor less light per watt.
3. I would *think* that manufacturing a low voltage high current bulb probably involves it's own increased level of complications, minor imperfections in filament size can have a more substantial influence on behavior than in a higher voltage design, where the same imperfection would have only a minor effect on behavior.
