IMG 0410

Excitation of the phosphor coating of an evacuated high pressure sodium lamp by electrostatically induced surface charges.
This demonstration appears similar to the effect first observed by Francis Hauksbee in 1705, in which he discovered that light could be produced by rubbing an evacuated glass sphere containing a small amount of mercury.
In this case the glass bulb is under hard vacuum and contains no mercury, but is internally coated with europium-activated yttrium vanadate phosphor. Electrostatic surface charges can be generated by rotating the bulb against the hands, and leads to excitation of the phosphor which produces its characteristic red emission.
The effect is not normally observed with lamps - usually such kind of phosphor coatings are only used on mercury vapour and metal halide lamps having nitrogen-filled outer envelopes which prevent the establishment of surface charges, while the evacuated high pressure sodium lamps do not generally use a fluorescent material as the light-diffusing coating of their outer envelopes. However for a few years Sylvania produced lamps such as this one, having this unusual combination of materials.

[@FrontSideBus]

Now that is very interesting!

[@cremationpete]

Static causing ionisation in the outer envelope?