GB1493270A - Discharge lamps - Google Patents

Abstract

1493270 Starting discharge lamps MATSUSHITA ELECTRONICS CORP 24 Dec 1974 [28 Dec 1973] 55745/74 Heading H2H [Also in Division H1] A conductor 14 attached to the outer wall of the arc tube 1 of a discharge lamp, having a filling of sodium, a metallic buffer gas and a starting gas, e.g. a neon-argon mixture, is located near the electrode at one end of the tube and is connected to the electrode at the other end of the tube by an arrangement which permits a starting potential to be applied initially to the conductor 14 and then, once the arc has been struck, allows the potential of the conductor 14 to float. This arrangement may comprise an element 15 having two opposed spaced apart electrodes carried by an insulating bead to provide a capacitive coupling between the conductor 14 and the electrode. Alternatively, as shown, the arrangement may comprise a bimetal switch 18 in parallel with the element 15. With the bimetal switch 18 closed, the lamp can be started at a low voltage so there is only a low potential difference between the outer and inner surfaces of the alumina tube 1 at the location of the conductor 14. The temperature and consequently the sodium vapour pressure are also low so there is no diffusion of sodium through the envelope and no blackening at the location of the conductor 14. As the temperature increases the bimetal switch 18 opens and the conductor 14 is left "floating". The bimetal switch may be heated additionally by a heater connected in series therewith. In an alternative arrangement the lead to the conductor 14 is extended through the outerenvelope 11 to an external switch. The outer envelope 11 may contain getters 12, and may be evacuated.