Abstract: A device for lighting a medical treatment field is disclosed and includes an optical member for focusing a plurality of light rays. The device also includes a prism assembly formed of a plurality of sectors of prisms. Each prism has an entry face and an exit face. The vertices of the sectors are substantially located in the center of the prism assembly. The sectors of prisms are configured and dimensioned so that the optical focusing member can focus the plurality of light rays generally onto the entry faces of the prisms. In addition, the device includes a mechanism for displacing at least a predetermined number of sectors such that the exit faces of the prisms of the predetermined sectors can be selectively positioned in one of a generally planar or a non-planar configuration. In an alternative embodiment, the device includes an optical focusing member and a prism assembly wherein the exit faces of the prisms are generally arc shaped along the length of the sector.