That's backwards. I'd suspect the ballast, not the lamp. Is the ballast
inductive or solid state? I'd try hooking up a 100 W light bulb as a test to
replace the lamp, disconnecting the starter system if possible. If the lamp
glows fully or not at all I'd suspect the ballast.

N
I assume that it's an electronic ballast as it uses transistors to limit
current as opposed to a coil. i assume those should be keeping things
from reaching a current where a fuse would blow? i think this is starting
to make a bit more sense.
Thanks