The reflector has a highly-polished or slightly-roughened surface, and shines onto an oblong light-inlet surface. This slides parallel to the light source, and contains the inlet edge of a light-guide glass. It is built up to set rules dependent on its position in relation to the lamp and edge. When the opening angle of the lamp seen from the reflector at right angles to the lamp, is less than the opening angle of the light inlet, a line perpendicular to the reflector bisects the angle between the lamp tangent (LR) at the side furthest from the inlet surface and the line joining the reflector (3) to the nearest edge of the surface. USE/ADVANTAGE - System selects reflector shape giving maximum light transmission into the inlet edge.