A flat illumination device, includes a base plate and a front plate which are connected to form an at least partially transparent vessel which, in its interior, has an ionizable fill. The blanket includes a body having an interior surface configured to face the workpiece. The clutch ring is made of an elastic material and selectively contacts with the clutch protrusion to supply elasticity to the rotation shaft during the rotation thereof. The apparatus also includes a second band constructed of a biologically inert material.