If they're round and you swap out the entire reflector assembly to replace a burned out bulb, you have sealed beams.
This car is equipped with sealed beams:
http://www.oocities.org/sveinn.geo/gallery/w123_300D_Turbo.jpg
This car is equipped with European-style headlights, where you only replace the inner bulb:
http://farm4.static.flickr.com/3176/2980395721_5a1938fb98.jpg
Sealed beams were required in the US until some time in the mid-80s; I forget what the cutover year was.