a light box for x - rays is made by using a graphics screen coupled to a microprocessor , with the screen being used with inverse brightness . under these conditions , the graphics screen emits light at nearly all points , other than special locations whose positions can be controlled by means of a control box . an x - ray negative to be examined is placed over the graphics screen . the control box is used to move the non - illuminated regions of the screen to point to special locations in the negative . the light box is particularly applicable t studying stereographic negatives for mammography . it makes it possible to determine more quickly and more accurately the locations of lesions in breasts under examination .