The ornamental design for a lightingdiffuser, as shown and described.
FIG. 1 is a top perspective view of a lighting diffuser;
FIG. 2 is a top plan view of the embodiment shown in FIG. 1;
FIG. 3 is a bottom plan view of the embodiment shown in FIG. 1; and,
FIG. 4 is a front elevation view of the embodiment shown in FIG. 1, the rear, right side, and left side elevation views being identical to the front elevation view shown.
The dash-dot-dot-dash broken lines in the drawings represent borders of unclaimed portions of the lighting diffuser and form no part of the claimed design. The appearance of any portion of the lighting diffuser within the dash-dot-dot-dash broken lines forms no part of the claimed design.