Abstract: In the invention, an active electrooptical filter cartridge comprises a flat housing (10, 12, 16) forming a closed cavity, which is completely filled with an optical transmissive resin (44, 52, 56, 60, 62) and an active device (14). The active device (14) is completely surrounded and fixed by the resin and comprises as components an LC panel (30, 32) positioned between light-transmissive portions (24, 28) of opposite main walls (10, 16) of the housing, a sensor means (34, 36) for detecting incident light on the filter cartridge, a circuit means (38) for controlling the LC panel (30, 32) in response to an output from the sensor means (34, 36), and a power supply means (40, 42) for operating the active device (14). The filter cartridge can be manufactured with the same dimensions as a passive, darkened filter glass, e.g. for use in welding helmets.