The ornamental design for a lampbead, as shown and described.
FIG. 1 is a top, front and right side perspective view of a lamp bead showing my new design, with the wires broken away to indicate indeterminate length;
FIG. 2 is a bottom, rear and left side perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines in the drawings illustrate portions of the lamp bead which form no part of the claimed design.