. . . "For practical purposes, it is preferred that all voltage responsive switches 22 through 31 be of identical construction and ideally would have a characteristic, such that, when conductive, i.e. in an ???on ??? or ???closed ??? condition, the impedance thereof have a value equal to the impedance of the filament of the corresponding light bulb and, when nonconductive, i.e. in an ???of??? or ???open?" .