Fluorescent screen glow

This experiment does have some features of a direct vision observation. First, the glowing spot is directly visible. Second, it is easy to imagine an invisible stream of particles hurtling through the triangular hole in the electrode to crash against the fluorescent screen in a burst... 

Other uses are to produce phosphorescence and fluorescence in organic compounds and for scintillation screens on instruments used to detect radiation. Radium salts were used in the past to paint the dials of luminous clock faces that glow in the dark. 

Some phosphorus compounds glow in the dark as they emit light after absorbing radiation. This makes them useful in special fluorescent lights and the color screens of television sets and computers. 

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