Wide-area solid-state illumination devices and systems employing a thin and flexible sheet of an optically transmissive material having at least one broad-area surface patterned with light scattering surface microstructures such as microdots of a non-absorbing UV curable ink. Light is input into the thin and flexible sheet using a number of compact solid-state light sources, such as LEDs, optically coupled to one or more edges or to one or two of the broad-area surfaces defining the thin and flexible sheet. Each surface microstructure forms a semi-opaque layer that extracts light from the thin and flexible sheet and causes light emission from both opposing broad-area surfaces of the sheet.