pitch of the locks and keys are selected such that only the keys on a short side of one tile can fit in the locks on the short side of another tile and only the keys on a long side of one tile can fit in the locks on the long side of another tile the conductors 72 75 are positioned to extend between opposite key lock pairs to act as buses between connected tiles and also electrically contact the bottom anode and cathode leads 29 30 of the light sheet 68 the conductors 72 75 may overlap edges of the bottom plate 60 to ensure a good electrical connection to corresponding conductors in an attached tile when the tiles are connected together the corresponding conductors push tightly against one another the keys and locks may be circular as shown rectangular triangular or any other shape fig7 is a perspective view of a light sheet 68 mounted on the top surface of the bottom plate 60 and the top plate 70 affixed over the light sheet 68 to form a tile 84 a conductive grease may be applied to the abutting surfaces of the bottom anode lead 29 fig1 or 3 of the light sheet 68 and the positive conductor 74 fig6 and between the bottom cathode lead 30 of the light sheet 68 and the negative conductor 75 to ensure good electrical contact over a wide area the light sheet 68 may be affixed in place with any type of adhesive and uniform pressure fig8 illustrates how the tiles 84 a and 84 b identical to the tile 84 of fig7 are interconnected with each other and also illustrates.