headlights on older vehicles ?

heyo

i have a 1978 GMC Sierra and am interested in the halogen style headlights.. due to poor visibility of the original headlights. does the whole unit have to be replaced or does one just purchase better bulbs ??

prolly is a real amateur question but.. sorry /ubbthreads/images/%%GRAEMLIN_URL%%/smile.gif

[puppy]

the whole unit needs to be replaced as in the bulb..it is all one unit and sealed..is it a style like this...

http://img153.imageshack.us/img153/8865/dsc1168ni1.jpg

thank you!
i was looking into this unit

http://www.lmctruck.com/features/cc/CCEL1.htm

[Soundbear]

There's gotta be some plastic covers somewhere to protect those expensive bulbs.