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 a front elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dashed broken lines in the Figures show unclaimed portions of the lighting device. The line shading in FIGS. 1-6 show surface contours, not surface ornamentation. The rear view is omitted and forms no part of the claimed design.