Would a bad alternator cause headlight flicker?

Is this a rapid flickering of the headlights, or do they just dim as the RPM's drop?

Just pull the alternator belt off and start the car and you'll know right away if it is the alternator bearings (or could be the water pump too). Also, hold the tip of a long screwdriver straight against the alternator housing and put the handle up to your ear while running, and you'll hear the bearing whirr coming through the screwdriver if it is the alternator.