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I've noticed in the last two houses I've lived in that CFL bulbs will periodically flash even when not turned on. It's about one flash a minute, and it's not very bright. You can only notice it when it's dark. I originally thought it might be power in the CFL circuitry leaking out after being turned on, but the flashing continues even if the lights haven't been powered up for days.

The wiring in both houses was old to start with, but then redone with new wiring, RCDs and so on. There is no voltage between the contacts in the socket when I check it with a multimeter, so how are the bulbs getting power to maintain a constant flash?

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Are there dimmers, timers, occupancy sensors, or other similar devices used to control the light? – Tester101 Mar 11 '14 at 11:30
No, all are plain old wall switches. – stib Mar 11 '14 at 11:30
Are these lighted wall switches? – DoxyLover Mar 11 '14 at 18:56
If not lighted wall switches like @DoxyLover mentioned could be a wiring problem where a little bit of current is still flowing to the bulb when off. – OrganicLawnDIY Mar 11 '14 at 20:58
Transients are a possibility from nearby equipment. Is there a whole house surge protector? Do two nearby bulbs flash at the same times? – Bryce Mar 11 '14 at 22:39

Any leakage current will cause CFLs to flash. I had to replace my porch light timer with a relay type because the sensor in my original one used a very slight amount of current to test if the bulbs were installed and working. And here's a similar problem I have been having, for which I have not yet found a suitable solution: I have some LED spotlights on a dimmer that ties in to a circuit with two other incandescent lamp system on dimmers. Depending upon the setting of all three dimmers, the LED spots will flash. I think it is noisy contacts in the incandescent dimmers, and that small amount of pulsing is picked up by the LED circuit. It is not annoying enough for me to delay any of my other projects to address it, as it only happens occasionally, and is mostly triggered by the chandelier setting.

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