I have CFL's installed in a ceiling fixture. At night, with the power off, the bulb blinks about every 15 - 20 seconds. This bulb has been in the fixture for about 2 years and it just started doing this a few weeks ago. I know the ballast is built into these things. I've never seen any kind of fluorescent bulb do this in all my years, and I'm older than dirt. I'm pretty sure it's the ballast. Just looking to utilize someone's vast experience.

Fluorescent lamps can be seemingly activated by RF signals, or radio waves.

This phenomenon was used by some testers that were once on the market, you would hold and point a handheld device, that was actually a radio transmitter, at a lamp or fixture on the ceiling from the floor, if the lamp glowed it was fine.

There may be a new transmitter or a radio or TV station, or a HAM operator may be nearby causing the lamp to glow or flicker when the power is off.

Mabe try turning off breakers, then on one by one to see if from inside your house, and may help determine source.

I have one of those testers. I used to work for a petroleum distributor. I was in charge of maintenance of all their gas stations and I used this tester for all the fluorescent lights. The one I have has an expandable antenna, like the old AM radios, but you had to make contact with the glass to light up the bulb. Besides, there are two bulbs in this fixture and only one is blinking. I guess I should have mentioned that in my question. And, I just noticed I misspelled compact on my header. Sheesh.

What type of wall switch is controlling the lamp?