The ornamental design for a lightingdevice, as shown and described.
FIG. 1 is a front perspective view of a lighting device showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a top plan view thereof.
The dashed broken lines in the Figures show unclaimed portions of the lighting device. The oblique line shading in FIGS. 1 and 2 shows a translucent or transparent material. The bottom view is omitted and forms no part of the claimed design.