Abstract: The invention provides an illuminated board for use in sign boards, advertisement boards, drawing boards or similar planar objects to be illuminated comprising an elongate transparent and translucent wedge-shaped slab or prism with one essentially rectangular end face, two essentially triangular parallel side faces, one essentially rectangular smooth front surface and one essentially rectangular smooth rear surface, at least one light source arranged at said end face for illuminating said end face, one opalescent front panel arranged in a distance from said front face and essentially parallel to said front face and one reflective rear panel arranged in a distance from said rear face and essentially parallel to said rear face.By arranging the panels and the wedge so that they are not in mutual contact an attractive uniform and bright illumination can be practically obtained even in sign boards in sizes up to 1.1 m by 1.5 m.