When I switch off the tube-lights , their ends blink for a considerable time. I thought as they were old, there might be some problem. But to my utter surprise, when a new tubelight was switched off, same phenomenon occurred. Is there a physical explanation?
Another phenomenon is that, when there is low voltage, continuous black waves can be seen traveling through the tube-light. What are these? Is this an illusion, or is there any reason?
The light from a fluorescent lamp is produced by an electric current discharging through a gas, typically mercury vapour, which releases photons in the UV-range. These are then absorbed by a thin phosphor coating on the inside of the glass tube, which re-emit a photon in the visible spectrum.
In order to generate the required voltage and maintain an arc through the gas, these lamps require a 'ballast' which, in the simplest case, consist of an inductor, or a solid-state electronic circuit, which generates a high enough voltage to ionize the gas and produce a discharge current through the tube. In some cases, a 'starter' filament is used to heat a cathode which discharges electrons into the gas. This 'starter' is disconnected once electric discharge is maintained through the tube.
When a starter is old and worn, there may be insufficient discharge current through the tube to keep the gas ionized, which can result in 'blinking' at the ends of the tube, as the starter filament is brought in and out of operation.
Depending upon the type of ballast and/or starter, you may need to replace the starter, eg: some electronic ballasts incorporate a the 'starter' function, in which case you may have to change the ballast. A worn lamp is usually indicated by dark patches at the ends of the tube.
A low voltage would typically result in repeated flickering at the ends of the tube or the lamp will not light at all, depending upon how low the voltage was. Some lamps may not
The 'dark waves' which appear through the tube at low voltage are the result of insufficient temperature within the tube to achieve full ionization of the gas, which could result from a low line voltage causing the starter to malfunction.
As for the blinking after you switch it off, I think I would be checking your wiring. The neutral might be being switched instead of the active. The most likely possibility is the small current caused by capacitance between the wires going down to the switch, especially if it's a long run. If the fitting had a power factor correction capacitor, that would stop it. The black waves (striations) are a common feature of gass discharges at low current. They are caused by the electrons running out of energy after they excite the gas atoms then have to be accelerated again to excite the next bit.
