The ornamental design for an undulatingflexibleilluminationsheet with opposing light-emitting surfaces, as shown and described.
FIG. 1 is a perspective view of an illumination sheet incorporating the design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof; and,
FIG. 4 is a left-side view thereof, the front-side view being identical to the left-side view and the back-side and right-side views being mirror images of the left-side view.
The arrows depicted in broken lines indicating light emission are for environmental purposes only and form no part of the claimed design. The regions of oblique surface shading do not imply any particular reflectivity of the surfaces of the illumination sheet, only that light is emitted therefrom.