A illumination device comprises a light guide having a first end for receiving light and configured to support propagation of light along the length of the light guide. A turning microstructure is disposed on a first side of the light guide configured to turn light incident on the first side and to direct the light out a second opposite side of the light guide, wherein the turning microstructure comprises a plurality of indentations. A cover is physically coupled to the light guide and disposed over the turning microstructure. An interlayer is between the cover and the light guide, wherein the interlayer physically couples the cover to the light guide. A plurality of open regions is between the interlayer and the plurality of indentations. Various embodiments include methods of coupling the cover to the light guide while preserving open regions between the cover and plurality of indentations.