I think there is a bit of a confusion here.
A bulb rated at 50W will NOT draw 50 amp when connected across 1 V. The watt rating is wrt a fixed voltage.
A bulb can be discribed as a length of wire with known resistance. For the sake of simplification, assume this resistance to be invariant over temperature changes (fixed resistance)
The correct formula for power should be W=I X I X R
Given R= constant, W therefore is dependent on the value of I.
HOWEVER, V=IR, given fixed R, therefore I=V/R. (I is proportional to V)
Assume V=1V, R=1 Ohm, I=1amp therefore W=1W
Assume V=50V, R=1 Ohm, I=50amp thefore W=250W
Cheers
