The ornamental design for a lighttunnel, as shown and described.
FIG. 1 is a front, right side, bottom perspective view of the light tunnel of the present invention with a floor and handrails shown in broken lines to show the light tunnel in an installation for use;
FIG. 2 is a front, left side, top perspective view thereof;
FIG. 3 is a left side perspective view thereof, the right and left sides being mirror images;
FIG. 4 is a front, right side, bottom perspective view of a single element of the light tunnel of FIGS. 1-3;
FIG. 5 is a front view thereof;
FIG. 6 is a front, right side, top perspective view thereof;
FIG. 7 is a left side perspective view thereof, the right and left sides being mirror images;
FIG. 8 is a view as in FIG. 1, without the floor and handrails;
FIG. 9 is a view as in FIG. 2, without the floor and handrails; and,
FIG. 10 is a view as in FIG. 3, without the floor and handrails, the right and left sides being mirror images.
Elements shown in broken lines form no part of the claimed design.