CF Flashing when off

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.

Sylvia.

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?

"Mike Manuka"

** 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.

** NO.

** 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

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.

the small current is providing power to the LEDs

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.

--
Regards
Blue

Remove ZX from email address to reply directly.

"aussiblu"

** 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

"aussiblu"

** 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.

1. The vast majority of CFLs do not either.

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

Conclusion:

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

QED.

...... Phil