The ornamental design for a three sided lightstick, as shown and described.
FIG. 1 is a front, top perspective view of a three sided light stick;
FIG. 2 is a side view thereof as seen from the right-hand side of FIG. 1;
FIG. 3 is left-rear view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken line showing is for environmental purposes only and forms no part of the claimed design.
The break lines have been applied to the drawing views to indicate that no particular length, with the understanding that the undisclosed portions of the light stick not shown in the drawings forms no part of the claim design. Patentability is based only on those portions of the article that are shown in solid lines.