FIG. 1 is a perspective view of a lamp holder showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left elevational view thereof;

FIG. 5 is a right elevational view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The portions of the lamp holder shown in broken lines form no part of the claimed design.