The article describes research work that can help students observe and experimentally research the effects caused by the emission component of the filament current in fluorescent lamps' cathodes. When analysing the work of electronic devices--multi-purpose lamps that use thermionic emission--research usually focuses on the current caused by the movement of electrons affected by the electric field between the cathode and the anode, and the cathode's filament current is considered to be associated only with the movement of electrons through the metal conductor. However, the electric field's potential drops along the cathode, which gives rise to the emission component of the filament current by the transfer of the emitted electrons along the cathode. The most convenient research object for this effect is a "fluorescent lamp with a direct-filament cathode," where the emission component of the filament current manifests itself in the glow of the nearcathode space. The practical implications of the work lie in clarifying the algorithm for determining the lamp's cathode temperature by its resistance.