Selecting transformer voltage for lamp drawing 32W and 6.6A
Tungsten Bulbs have a well known positive temperature coefficient or PTC where the filament resistance rises x10 from cold to hot.   Halogen gas bulbs have higher MTBF at elevated temperatures with a metal vapor recycling mechanism than std.  Tungsten filaments which just use less expensive inert Argon gas. 

Thus when random startup occurs at peak voltage, the current can be 10x the rated hot current, which causes radial filament forces to possibly break a weakened filament at 1500 hrs MTBF such as conventional tungsten lamps with unregulated sources rather than a much higher MTBF rating with a constant current source for higher reliability.

You could use DC as long as it was constant current regulated.  Operating at a higher voltage or constant voltage reduces MTBF. But I don't know about airport runway certification if that is allowed as it is not exactly the same performance with mismatched bulbs.  AC method uses voltage transformers per bulb with current limiting/compensation.

Operating at a lower voltage raises MTBF as long as startup current is not exceeded but also reduces brightness.

This is why household bulbs tend to go poof when you  turn then on after their normal lifetime.  Also if they are enclosed without air flow and run hotter than normal, this will reduce MTBF significantly.