A lighting device (100, 300, 400) is disclosed. The lighting device comprises a light source (110, 310, 410), an at least partially light transmitting envelope (120, 320, 420) and a dispenser (140, 340, 440). The envelope is arranged to define a sealed space (130, 330, 430) in which at least a portion of the light source is arranged. Further, the dispenser comprises a chemically reactive substance and is adapted to gradually release at least some of the chemically reactive substance to the sealed space so as to reduce contaminants and by-products that may be present in the sealed space.