Abstract: A light-ray indicator having a support on which is mounted by a universal joint a housing containing a radiation source and provided with a weight at the lower end so as to seek a plumb line. The universal joint forms a portion of an electrical circuit which connects the radiation source contained in the housing a power supply mounted on the support mounted externally of the housing and universal joint, with an adaptor unit including an adjustable mirror being mounted on an upper end of the housing so as to permit the mirror to deflect a radiation beam received from the radiation source through an angle variable with respect, but intersecting, an axis along which the beam is originally emitted from the radiation source.