The present invention relates to a light-exposure assembly. It includes a mask which is placed on a mask stage to accept exposed light. A work-piece stage is placed under the mask stage. A projection lens is placed in between the mask stage and the work-piece stage to form an image on the work-piece stage by accepting the exposed light. A first mark is carved on the mask to detect the parallel-degree of movement of the mask stage and the work-piece stage. A second mark is carved on the mask to measure changes in magnification of a projection lens by moving together the above first mark. A third mark is carved on the mask to determine focus point of the projection lens. A fourth mark is carved on the work-piece stage to assist the first and second marks. A first optical detecting part is placed on the work-piece stage, on which a fourth mark is carved to assist the movement of the first and second marks, and to detect the exposed light. A second optical detecting part is placed on the above work-piece stage to detect the exposed light. The photoreceiver has multiple functions to detect automatically, by a kind of photoreceiver, light-uniform-rate of exposure of the light source, to perceive changes in the magnification of a projection lens, to calculate the parallel-degree of movement in the mask stage and the work-piece stage, and to calculate the focus-position of the projection lens.