Which one of the following is the secondary source of light in a -fluorescent lamp ?

In a fluorescent lamp, the production of visible light occurs through a two-stage process. The primary source of radiation is the mercury vapour, which, when excited by an electric current, emits ultraviolet (UV) light [t2][t4]. However, UV light is invisible to the human eye [t9]. The secondary source of light is the fluorescent (phosphor) coating on the inner surface of the glass tube [t1][t7]. This coating absorbs the high-energy UV photons and re-emits that energy as visible light through the process of fluorescence [t2][t8]. While argon gas is present to facilitate the discharge and protect the electrodes, it does not serve as the light source [t1][t7]. Therefore, the phosphor coating is the component responsible for converting invisible radiation into the visible glow we perceive, making it the secondary source [t4][t6].

Sources

1. [1] https://www.sciencedirect.com/topics/computer-science/fluorescent-lamp