Low-pressure mercury vapor discharge lamp

Low-pressure mercury vapor discharge lamp has a light-transmitting discharge vessel (10) enclosing, in a gastight manner, a discharge space (13) provided with a filling of mercury and a rare gas. The discharge vessel (10) comprises discharge means for maintaining a discharge in the discharge space (13). The discharge vessel is provided with a source of mercury (7). In addition, the discharge vessel is provided with a releasing means (8) for the controlled release of mercury vapor from the source of mercury. The releasing means is operative in response to a condition of the low-pressure mercury vapor discharge lamp, the condition being a characteristic of the discharge lamp and/or a pre-determined time interval. The discharge lamp according to the invention operates under unsaturated mercury conditions. Preferably, the releasing means is operated via a switch device, preferably comprising a reed relay.