Naked Science Forum

General Science => General Science => Topic started by: justinhood on 17/12/2009 22:21:54

Title: What causes fluorescent tubes to flash?
Post by: justinhood on 17/12/2009 22:21:54

I have a bathroom mirror which has 2 tubes turned on by a pull cord and this has a separate recd with 5 amp fuse.

when i switch the lights off about a minute later the tubes flash very quickly oust once? Then it can be off for hours and suddenly there is a very quick flash from the tubes?

Does anyone know why?

Thanks
Justin

[MOD EDIT - PLEASE PHRASE YOUR THREAD TITLES AS QUESTIONS, WHICH IS THE POLICY OF THE FORUM. THANKS. CHRIS]

Title: Re: What causes fluorescent tubes to flash?
Post by: chris on 17/12/2009 22:35:48

I have noticed the same phenomenon with CFLs - compact fluorescent (energy-saving) lamps in my house; in fact I had to remove the one from my bedroom because the sporadic flashing was keeping me awake at night (largely by causing me to lay in the dark speculating as to the cause!)

The best conclusion I can reach is that there must be some Earth-leakage or raised potential in the neutral line and that this is being soaked up by the capacitors in the starters for the tubes; when it reaches a certain threshold this energy is presumably spontaneously discharged through the lamps causing the flicker.

I live in an old house with prehistoric wiring; so this comes as no surprise to me though as to the source of the raised potential on the neutral causing the lights to flash, remain in the dark...

Chris

Title: What causes fluorescent tubes to flash?
Post by: Madidus_Scientia on 18/12/2009 03:45:55

This thread may be of interest http://www.thenakedscientists.com/forum/index.php?topic=26341.msg280648#msg280648

Title: What causes fluorescent tubes to flash?
Post by: justinhood on 18/12/2009 23:06:11

Thanks for response. The switch is mechanical ie its a pull cord which clicks on and off and the lamp is on a 5 amp rcd. If it was earthing would the rcd not trip out? If there is a small current running after its is switched off how does that happen? ie is it a wiring fault on the mirror itself and is it dangerous?

thanks
justin