is this a projector style lamp, if it is they have a beem pattern that stays mostly flat with a rise at the centre line which then heads of to the left flat.
A bit like the picture below. It's crude i know but it gives you an idea.
I have struck bulbs that have a bent filament, incorrect installation, mositure, dull lens.
Thats pretty much it.
Sometime the cut off on these headlights isn't that noticable.