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I have a energy saving spiral light bulb in my kitchen. In exactly every 27 seconds, the first segment of the bulb faintly flashes when the switch is off. And not once, repeatedly every 27 seconds. This weird situation occurs for more than half and a year. What can be causing these flashes? How can I prevent it if it spends energy or has safety risks?

PS: A new spiral bulb does the same thing. And the bulb doesn't flash when I remove from socket.

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It's likely related to the switch: what kind of switch? Can you post a photo? Age of home? Location? – Bryce Jul 10 '14 at 17:10
up vote 7 down vote accepted

For this to happen there must be some voltage to the light socket. It may not be noticeable with a standard incandescent bulb because it apparently is not the full voltage and current. If you are comfortable in what you are doing, you could measure the voltage across the two wires and ground to see what you get. Incorrect wiring could be the problem, such as an improper shared neutral leg, or the neutral being switch instead of the hot leg. This can be found using a voltmeter and referencing to a known ground. If your not sure, leave it to an electrician. Wiring is not a hobby, and can be lethal!

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A cause of this could be an electronic/magenetic dimmer on the light versus a standard single pole single throw (SPST) switch. The electronic/magentic dimmers leak a very small amount of current. With incadescent lights, there is not enough power to cause the filament to glow, however it is enough to cause your flourecent light to intermittently light up. To prevent it you can use a rheostat-based dimmer instead of an electronic dimmer, or just a plain-old switch.

As another answer said, it could be a wiring problem too. In addition to checking with a multimeter, I'd also visually inspect all of the switches and the wiring at the fixture. Replacing the switches is a cheap thing to try as well, and because it is a 3-way, there is more room for error.

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The switch is not a dimmer but single pole double throw. – sevenkul Jan 27 '12 at 22:48

Is your switch lighted/illuminated (something like the picture)?

When I put in CFL bulbs in sockets with lighted switches we got the same situation that you described. I believe the cause is the same as what @Steven already described. lighted light switch

As for a solution, that might be a good topic for a new question. :)

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The link at the end explains the flash and gives solutions.

Let me grab some excerpt from it:

Why does the CFL bulb flash? "Many times this is due to the circuit inside the CFL charging up, even when the bulb is off. This happens many times when the CFL bulb is being controlled by an illuminated wall switch, because the wall switch uses the CFL bulb itself as neutral. When the wall switch is on, the CFL bulb gets full line voltage. When the wall switch is off, the CFL bulb is the neutral for the light of the wall switch, causing a tiny current to flow through the CFL bulb.

This tiny current charges up the capacitor in the CFL bulb, until it releases it's energy. This cycle can repeat once every few seconds."

How to fix the flash? "put a bleeder resistor inbetween the two contacts of the light bulb. What this resistor does is cause the tiny current to pass through it, when the wall switch (or whatever causes the tiny current) is off, instead of charging the capacitor of the CFL and causing it to flash. "

http://www.instructables.com/id/Stop-CFL-lights-from-flashing/

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-1 Link only answers become useless when the link goes bad and are frequently confused with spam. Be sure to provide context around the link and quote relevant content in case the link goes bad. See how to answer for more details. – BMitch Jul 10 '14 at 17:22
    
@BMitch, I have put texts in place of the link. – zhanxw Jul 11 '14 at 18:52
    
Thanks, I've removed my -1. – BMitch Jul 11 '14 at 21:18

First to explain the reason. The switches with light in the button are circulating small current through the lamp in the off stage. This current must circulate without problems. The conflict, problem is with energy efficiency lamps as LED and CFL and LFL when in their electronic inside doesn't contain X2 EMC suppression capacitor which is creating path for circulation of this small current. Or for switches without light button the reason can be the parasitic capacitance + leakage resistance of the cable which is producing small parasitic current through the lamp. My solution (it is tested and applied) is: Just put in parallel to the lamp externally 1 capacitor X2 type 100-220nF with discharging resistor and ballast resistor, that is all. I have some where detailed calculations for values. For more details you feel free to contact with me: aydin_halil@yahoo.com But this is for technical guys not for amateurs, It can be dangerous for amateurs! Good Luck!

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Welcome to Stack Exchange. Modifying the ballasts of your bulbs seems like a bad idea, and a great way for an amateur to start a fire in their house. – Daniel Griscom May 19 at 11:49

The capacitance between the wires of the cable to the switch is enough to provide the current needed to slowly charge up the CFL internal power supply. The capacitance can be as small as a few hundred picofarad but this is enough. Rewire as two separate cables to the switch to reduce this capacitance.

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