The ornamental design for a decorative lightsystem, as shown and described.
FIG. 1 is a perspective view thereof;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The dashed lines in the drawings depict portions of the decorative lighting system and form no part of the claimed design. The dash-dot lines in the drawings depict an internal channel of the decorative lighting system and form no part of the claimed design.
The decorative light system is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.