a headlight that is designed for an hid bulb will be designed to disperse the light correctly & give you a very usable & correct beam, most times when a headlight that is NOT designed for an hid, but an hid is stuck in there anyway, it will just not work the same.
there are 3 general types of hid bulbs, ones that are designed for reflector housings, ones that are designed for projectors, & the third type, brought on by the aftermarket, is a hybrid type that is claimed to be able to perform well in either. this third type does not perform very well in either type of application really & should be avoided.
d2r=reflector housing
d2s=projector housing
d2c=aftermarket compramise
if at least a d2r type bulb is used in a reflector housing it can be not too bad, but will never be as good as if the headlight reflector & lense was actually designed for the hid in the first place, & when the wrong type bulb is used it can be pretty bad....