Low-pressure discharge lamp with filament having protective coating

摘要

At least one of the electrodes (6a) has a coil (60a) of a refractory metal which is electrically connected to current supply conductors (7a, 7a') which extend to outside the discharge vessel. The coil (60a) has a central portion (61a) which is coated with an electron-emitting material and an end portion (62a, 62a) on either side thereof, which end portions are covered with a protecting material which is mainly formed by one or more oxides of calcium and/or magnesium.