Abstract: A method of selecting low-pressure mercury discharge lamps comprising a luminescent layer, the luminescent layer being excited and the low-pressure mercury discharge lamps being selected in dependence on the emission spectrum of the visible light emitted by the luminescent layer. The luminescent layer is excited by a light source arranged outside the low-pressure mercury discharge lamp and which generates ultraviolet radiation having a wavelength above 300 nm. This makes it possible to use the presence of a blue-luminescent substance in the luminescent layer as a selection criterion for both leaky and intact low-pressure mercury discharge lamps.

Abstract: Low-pressure gas discharge lamp having a discharge vessel which comprises a plurality of parallel tubular portions which are interconnected in series by means of one or more coupling links engaging those portions substantially transversely, the discharge passing through the coupling link(s) and at least the major parts of the tubular portions during operation of the lamp, a coupling link engaging a tubular portion at a distance from one end of a tubular portion so that a cool spot is created in the lamp at that end.

Abstract: Low-pressure mercury vapor discharge lamp having a closed elongated lamp envelope and comprising at least two electrodes disposed near a first end of the lamp envelope, at least one electrode is situated at the end of at least one inner tube situated within and sealed in a gas-tight manner to the lamp envelope, this inner tube having at least one opening to the inside of the lamp envelope, the inner tube being U-shaped.

Abstract: A low-pressure gas discharge lamp having an inner tube in the discharge space limited by a lamp envelope the outer wall of which inner tube is provided with a luminescent coating, the portion which is provided with this luminescent coating facing away from the portion of the inner tube which is nearest to the wall of the lamp envelope.