a variable reflectance cover for a sranning system . the cover comprises a backing moveable through a plurality of positions . moving the backing through the plurality of positions varies the reflectance of the cover . in one embodiment , the backing is an endless rotatable belt . in a second embodiment , the backing is a removable panel having a first side with a first reflectance and a second side with a second reflectance . in yet a third embodiment , the backing includes polarizers placed adjacent to a reflective panel . rotating one polarizer relative to another varies the reflectance of the cover .