U.S. Philips Corporation

Abraham L De Smit

Jean J Heuvelmans

A lighting unit according to the invention comprises a supply unit (1) and a low-pressure mercury discharge lamp (2). The low-pressure mercury discharge lamp has a light-transmitting discharge vessel (3) which is provided with a luminescent layer (3) on an inner surface and which encloses in a gastight manner a discharge space (4) which is provided with a filling comprising mercury and one or several rare gases. A first (5a) and a second electrode (5b) are arranged in the discharge space, each comprising a coiling of a metal wire coated with one or several electron-emitting metal oxides. Each electrode is electrically connected to a respective current supply conductor (6a, 6b) which extends to outside the discharge vessel (3). The current supply conductors are electrically connected to the supply unit outside the discharge vessel, the unit ignites the low-pressure mercury discharge lamp in the state upon switching-on. During nominal operation, at least a portion (5a*) of each electrode (5a, 5b) passes an electrode current Iel having an effective value Iel which is at least 1.8 times the minimum electrode current Ip4 required for thermal emission. The lighting unit according to the invention has a long switching life.

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Terneuzen, Netherlands

Abraham L De Smit