We claim the ornamental design for a lighting device, as shown and described.
FIG. 1 is a perspective view of the lighting device;
FIG. 2 is a front view of the lighting device of FIG. 1;
FIG. 3 is a rear view of the lighting device of FIG. 1;
FIG. 4 is a right side elevation view of the lighting device of FIG. 1;
FIG. 5 is a left side elevation view of the lighting device of FIG. 1;
FIG. 6 is a top view of the lighting device of FIG. 1; and,
FIG. 7 is a bottom view of the lighting device of FIG. 1.
The broken lines showing in the drawings are included for the purpose of illustrating unclaimed portions of the lighting device and form no part of the claimed design.