The ornamental design for a lightingdevice, as shown and described.
FIG. 1 is a front perspective view of a lighting device, showing my new design;
FIG. 2 is the front view thereof;
FIG. 3 is the left side view thereof;
FIG. 4 is the right side view thereof;
FIG. 5 is the rear view thereof;
FIG. 6 is the top view thereof; and,
FIG. 7 is the bottom view thereof.
The broken-line disclosure in the views is understood to represent a portion of the article in which the claimed design is embodied, but which forms no part of the claimed design.