Abstract: An x-ray apparatus including an x-ray source with a primary radiation diaphragm attached thereto has a luminescent foil disposed in the interior of either the x-ray source or the primary radiation diaphragm at a location so that the x-ray beam is incident thereon. Interaction of the luminescent foil with the x-ray beam causes the foil to emit light, which is conducted to an exterior of the apparatus by an optical waveguide. The light is therefore visible at a location at the exterior of the unit, such as in the housing, as a reliable indicator that x-rays are actually being generated.