We claim the ornamental design for a desk lamp, as shown and described.
FIG. 1 is a perspective view of a desk lamp according to the claimed design;
FIG. 2 is an enlarged detail of the bottom, right-side perspective view of the desk lamp in FIG. 1;
FIG. 3 is a left side view of a desk lamp according to the claimed design;
FIG. 4 is a right side view of a desk lamp according to the claimed design;
FIG. 5 is a front view of a desk lamp according to the claimed design;
FIG. 6 is a back view of a desk lamp according to the claimed design;
FIG. 7 is a top view of a desk lamp according to the claimed design; and,
FIG. 8 is a bottom view of a desk lamp according to the claimed design.
The design has been shown broken away to indicate that no particular length is claimed. The portions of the desk lamp shown in broken lines form no part of the claimed design.