of CFL Bulbs
I am writing this post because I have not seen too many articles or posts about an unusual feature of the latest types of quick start CFL bulbs where the bulbs flash when switched off.
What I have seen in two of my fittings are the bulbs give a small and short duration flash of light about once every 30 seconds or so - this even though the main light switch is switched off!!
The type of CFL bulb in question is the newer generation rapid start, i.e. reach full brightness quickly, the variety is usually of a spiral shape. The flashing is not generally noticeable by day, as the light output of the flash is quite small.
The first time this phenomenon was reported to me was when I received a late night phone call from my wife who was in the UK at the time and staying at a hotel. She called to ask if there might be some danger as the main light in the hotel room was flickering at regular intervals in the dark. As I was not sure of what might have been happening, I suggested she contact the staff and request a different room, if for no other reason than that the flickering would disturb her sleep. At that time I did not know about flickering CFLs, and the dangers of faulty wiring was on my mind.
The next time I came across the problem what when we had some house guests who awoke us worried about the light in their room flickering. I had just fitted a new rapid-start spiral CFL in the main fitting. I immediately removed the bulb and re-fitted the old 100watt filament bulb curing the problem.
Since then, I noticed the problem in a hall light with a similar type of CFL fitted. This time the flickering was causing no disturbance and I knew that it posed no danger - that light still flickers away all night.
I think that the cause of the flashing is induction in the wiring causing a tiny leakage of current into the bulb. When that leaked current builds up in the bulbs starter circuit, it tries to ignite the bulb, but there only being a very small current present, all you get is a weak little flash. The charge and discharge cycle happens all the time and the interval depends on the capacitors in the bulb circuit. Apologies if that does not sound very scientific - it is only an educated guess.
I have learned that you would need to consider this CFL flashing business in your choice of bulbs and in your choice of locations. A bedroom is about the last place you want one of these bulbs. The older slow start CFLs - the ones that take a while to brighten up - I have found - not to flash.
So my advice - choose your CFL bulb carefully and choose the place you install it with this flashing thing in mind!