A system for distinguishing a target key which opens a lock from at least one other connected key in a dark environment includes a magnet which is positioned adjacent to the lock, and which produces a magnetic field. The system further includes a light assembly which is connected to the target key. The light assembly includes a magnetically activated switch and a light source. When the light assembly is moved into the magnetic field of the magnet, the magnetically activated switch is activated and causes the light source to give off light, thereby distinguishing the target key from the at least one other key.