CF Flashing when off

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I remember reading here a number of months ago what causes CF fluoro bulbs
to flash when switched off.  I cannot find the post and can somebody please
explain again.

Would this also cause this condition. I bought 3 GU10 240v 1watt LEDs from
Bunnings for $10 each. All 3 are on the same switch. When they are turned
off they still give off a slight
light. There are 20 LEDs in each globe and they vary in brightness when
switched off.  At first I thought it was reflected light from other places
but when I turned off all the lights in the house they still had the same
glow I decided to remove a globe from the fitting and when I
did that the light faded completely after about 2 minutes so I assume there
is a capacitor in the globe. Then when I put the globe back in the fitting
the LEDs immediately began to glow again. I phoned the person who told me
about these LEDs at Bunnings and he just phoned me back and said his do the

Many thanks for your knowledge, expertise and time answering.

Re: CF Flashing when off
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The consensus seems to be capacitance in the wiring leading to the
switch, allowing some small current to flow even when the switch is off.
Never noticabled with incandescents, of course.


Re: CF Flashing when off
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I was wondering if someone could try this experiment.

Lay out a run of wire, two strands about 6 metres long, and connect the
end of each wire to one of these new bulbs. Next, extend the wires out
in opposite directions, like a dipole antenna. What happens to the
brightness of the bulbs? Is the lighting of the bulbs due to
"capacitance" or RF energy? Raise the wires up of the ground, like an
antenna, does it make any difference?

Re: CF Flashing when off

"Mike Manuka"
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** Inside every modern CFL, there is a high frequency inverter circuit that
operates from a DC supply obtained by rectifying the incoming AC supply
voltage.  The AC voltage at the lamp socket is fed via a bridge rectifier to
a small electro cap that charges up to circa 340 volts DC,  if the AC power
is 240 volts.  The high frequency inverter runs from this voltage.

Now, if there is *sufficient leakage current*  in the AC circuit that feeds
the light socket used by a given CFL, then the electro inside will SLOWLY
charge up to a DC voltage of around 60 to 80 volts  -  causing the internal
"kick-start" circuit to fire and make the CFL lamp flash ( rather weakly )
just once.  The small electro is partly discharged by this event and the
charging process begins again resulting in a stream of flashes at a rate
anywhere from once every 10 seconds to many times a second.

Not all CFLs do this and some are far more sensitive to such leakage than
others and the leakage current may be resistive or capacitive in nature.

A Philips  " Tornado " 23W CFL which I checked just today, flashes weakly
every 6 seconds or so if coupled to the AC supply via 2M ohms of resistance
or 1000 pF of capacitance.  Less resistance or more capacitance simply
results in more rapid flashing.

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** NO.

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** As you must know, white LEDs simply do not exist.

So called white LEDS are actually blue or violet LEDs with a special
phosphor coating that converts part of the LED's light output into yellow,
green and red  -  so the light  YOU see looks "white".

Such phosphors often have an " after-glow " when viewed in the dark after
some period of use or exposure to bright daylight.  Ordinary fluoro tubes do
the same and they have a phosphor coating on the inside of the glass tube
that converts invisible UV light to " white ".

.....   Phil

Re: CF Flashing when off
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The capacitance between the switched and unswitched live wires in the
cable run from the lamp socket to the switch lets a small current flow
this current whist not enough to light an ordinary lamp is sufficient
to slowly charge the capacitor in the CFL, when it's full enough the
CFL flashes.

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the small current is providing power to the LEDs

Re: CF Flashing when off
When I had this problem with cool white (but not warm white) CFs
I asked Nelson Lamps, the company distributing the CFand this is
their response:

"I have checked out your situation and can confirm that this
rarely occurs we have found after much research that certain
homes that are wired in a way where they are switching the
neutral that this may occur with these lamps."

Subsequently after finding I had no switching neutrals the
advice was:

"The flashing may be due to the capacitance properties of the
mains wiring.  Having the wires running together in common
insulation may make them act like giant capacitors and some
insulated wiring seems to do this more
than others."

They seemed a little puzzled and uncertain themselves so I still
wonder what the truth is. I can't complain though as they gave
me some free replacement warm white ones.


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Re: CF Flashing when off

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** Can you check the CFLs with a capacitance meter ?

Just connect the meter to the AC supply contacts on the base.

The ones that are very prone to "flashing" show a reading in the 10s of pF
while most others have a cap across the terminals of about 47nF to 100 nF.

......    Phil

Re: CF Flashing when off

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** The only interesting thing is the companies   REFUSAL
 to admit the  PROBLEM  lies with their damn CFLs.

The logic is so simple.

1.  No incandescent lamp does any such thing.

2.  The vast majority of CFLs do not either.

3.  Capacitance in all AC cabling is normal as is some leakage current.


The CFL  is not correctly designed to cope with NORMAL  levels of AC leakage
encountered in domestic lighting circuits.


......    Phil

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