4 Pack: Clear prismatic acrylic flat sheet replacement cover panels 22.5″ x 22.5″ x .100″ Shop ceiling light panels and a variety of other lighting products online Additionally, plastic ceiling diffuser panel thicknesses are measured from the peaks of the prisms, not the valleys. Some competitors will use a sheet that has had the valley’s ground out to save plastic. Be aware that not all flat sheets of the same thickness are of the same quality. Please make sure you need a 22 1/2″ x 22 1/2″ size light cover panel before purchasing it. this sheet is cut from a bigger size sheet. As a result, there can be a restocking fee charged if returned. Replacement light cover panels -find ceiling light panels at Fluorolite today. Fluorolite only uses high-quality sheets.