The ornamental design for a lightbulb and baseunit, as shown and described.
FIG. 1 is a front elevational view of a light bulb and base unit, including a hemispherical base, a generally spherical transparent cover, and a contact element, the rear elevational view being a mirror image; and,
FIG. 2 is a side view thereof, the opposite side being a mirror image.
The broken line showings of the specific simulated seams of the base and of the enclosed logo are for illustrative purposes only and form no part of the claimed design.