[Enthalpy]

Hello dear friends! Could you propose an explanation(s) for that?

When I switch off a fluorescent lamp, it glows for a few minutes. Not very strongly, so I see it better with my eyes accustomed to the night, hence staying outside the room when the lamp shines. Well known: fluorescent materials show some phosphorescence too, good, fine.

Now, while the phosphorescence is decreasing, I observe light flashes from the lamp. Not strong at all, but definite. Much shorter than 1s, after which the afterglow returns roughly to its previous intensity.

But what could cause this?

Mercury condensation drops that move and do... something? This particular bulb is compact, with a folded tube, and about horizontal.

Residual electric charge in the circuit that sparks as the dropping mercury pressure gets easier to ionize?

Lukewarm materials that contract stepwise due to some rubbing and catalyze the phosphorescent de-excitation?

Radioactivity or cosmic rays that de-excite the phosphors? The flashes happen only during the afterglow.

Something else? I'm a bit out of ideas here... Suggestions welcome!

[billnotgatez]

Defective ballast or internal circuitry (starter)?

[Enthalpy]

Maybe... The light bulb and its circuitry gets no more power from the grid, but capacitors can still hold charge.

These flashes are faint. Within the phosphorescence of the light bulb they're small but convincing, so they're very weak as compared with the bulb's normal operation, in fluorescence mode. One can see them only with the eyes accustomed to the dark.