Phosphorescent marking system

In a device of phosphorescent material on which lumincescent images are formed and retained for a period of time, said device comprising means for supporting said phosphorescent material, said phosphorescent material including a uniform distribution of a phosphor in a carrier, said support means permanently shielding a bottom surface of said phosphorescent material from phosphor activating light, said support means exposing a top surface of said phosphorescent material to phosphor activating light, the improvement comprising means for shielding said phosphorescent material top surface from phosphor activating light, said shield means being positionable over said top surface to maintain said phosphorescent material in a deactivated state and subsequently removable from said top surface to expose said top surface to phosphor activating light, a source of light and means for controlling exposure of selected portions of said phosphorescent material to said source of light to form an image on said inactivated phosphorescent material when said shield is removed, said image being retained for said period of time until activation of said phosphor has decayed to an inactivated state of an imperceptible level of luminescence.