The ornamental design for a head of a streetlamp, as shown and described.
FIG. 1 is a front, top and left-side perspective view of a head of a street lamp showing my new design;
FIG. 2 is a front, bottom and right-side perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a right-side elevational view thereof, the left-side elevational view is a mirror image;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view of the head of a street lamp attached to a pole.
The broken lines in FIG. 2 depict portions of the head of a street lamp that form no part of the claimed design. The broken lines in FIG. 8 depict environmental subject matter only and form no part of the claimed design.