CFL Flickering

[Peter P.]

I have a friend who's having a flickering CFL problem.

The bulb in question is in an outside fixture on a side porch.

It flickers at all temps.

The front porch has the same bulb but doesn't flicker.

We replaced the bulb but there was no change.

The switch operating the CFL is not illuminated (which I've read can cause the flickering), but IS in a 4 gang box with three other switches (presumably in parallel), one of which is a dimmer.

I'm wondering if the dimmer, being in parallel with the CFL switch, is the problem. I don't know what the dimmer operates but it could be a fan or incandescent lamp.

Could that dimmer be swapped to a florescent capable model even though it might be running a fan or incandescent bulb?

I know the easiest solution is to just replace the CFL in that fixture with a different type bulb, but it would be nice to have an explanation for this light's behavior.

Thanks for reading.

 

[Dennis Alwon]

Sounds like a bad socket on the fixture.


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[Dennis Alwon]

I am reopening this thread after communication with Op.

 

[gar]

141230-1224 EST

Peter P:

I don't believe you have parallel switches. You may have one terminal of several switches connected together and to a hot line. That is not parallel.

If two or more switches are in parallel, then the terminals on both sides of the switches must be connected together. With this arrangement all switches must be open for the circuit to be open, and any one or more closed switches makes the circuit closed. This would be referred to as positive logic "OR" circuit.

If the switches were connected in series, then it is a positive logic "AND" circuit. All switches must be closed for the circuit to be closed. Any one or more open switches opens the circuit.

With 3600 pfd in series with a CFL and supplied from 120 V 60 Hz I had no flashing. This is about 700,000 ohms of capacitive reactance.

A 33,000 ohm resistor in series with the CFL produced flashing, while 100,000 ohms did not.

It takes about 0.05 ufd to get flashing, about 55,000 ohms. This is way too much capacitance for you to encounter in residential wiring.

Measure the leakage current to your fixture. Replace the bulb with a screw-in socket. With the circuit turned off connect a 1 k 1/2 W resistor to the socket. Measure the voltage across the resistor. The reading will be 1 V per millampere. My guess is that 1 mA to 5 mA will be sufficient to cause flashing. If you have leakage current find the source.

Now the why. Many CFL inputs are a rectifier to a filter capacitor. There is not much current flow from the capacitor until a certain threshold voltage is reached, then current flows and the capacitor voltage drops, and the cycle starts over. This is a simple multivibrator. Easy to make with a neon bulb, capacitor, resistor, and a 100 V or so DC voltage source.

.

 

[Electric-Light]

Many CFLs are not dimmable and if they're not dimmable, they will go haywire even if you set it on maximum setting.

To dim CFLs, you need special dimmable ones and may need a special dimmer. Even then, compatibility is a hit and miss. Two wire dimming is a challenge for all except line voltage incandescent lamps. Dimming issues haunt CFLs, LEDs and low voltage, but in my experience, dimming is not nearly as troublesome with light emitting decorations.

 

[gar]

141231-0950 EST

Efficient troubleshooting of a problem with equipment requires a knowledge of how all the components in the system work. This information is quite lacking relative to various dimmers and electronic switches and various loads such as incandescent, CFL, LED, transformers, solenoids, and motors.

It is far better to work from basic knowledge rather than a list of items that are supposed to be compatible. Basic knowledge allows you analyze why you have a problem.

In a different thread, but generally the same subject area, I provided a reference to:

"Probing around the Lutron site I found this technical discussion
http://www.lutron.com/TechnicalDocum...Whitepaper.pdf .
This should help many understand the various problems of dimming various loads."

This is not directed at flickering CFLs, but gives you related background information.

If I did not previously mention a test that needs to be performed, then the test is to take the flickering bulb and put it in a controlled condition on a bench and see if it flickers. If it doesn't flicker, then the problem is with the circuit where it flickers.

.

 

[Electric-Light]

gar, your responses are going far over many reader's head..

 

[gar]

150101-0048 EST

Electric-Light:

If my responses are over someone's head, then they can ignore the response, study the response, or ask questions.

.