Macgravy
Newly Enlightened
Those hours, as stated in the Osram specifications, are life while operating on AC power not DC.Low-voltage halogen lamps are already designed to operate with direct current.
But there are types from the same manufacturer with different lifespans.
For example Osram 24V150W:
64640: 50 hours;
64641: 200 hours;
64642: 300 hours;
However, it is still true that the lifespan decreases if the lamps are operated with a little more than the nominal voltage, or increases if the voltage is lower.