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I am about to replace an ageing smoke alarm. The current one is battery powered, but I was thinking that it might be good to replace it with a mains powered one (no need to change battery, cannot be easily disconnected to stop it sounding, etc...).

In the instructions for many of the mains powered alarms I have seen, it says that they can be connected to a lighting electrical circuit, but only if the circuit does not have any fluorescent lighting attached to it. All of the bulbs in my house are energy saving, of two differing types:

Do these energy saving bulbs class as fluorescent lighting, or are the instructions referring to only the more traditional long fluorescent strip lights?

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2 Answers 2

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Both of the bulbs you show are fluorescent (or more specifically, compact fluorescents "CFLs"). Fluorescent bulbs are characterized by their long opaque glass tubes and the electrical ballast in the base of the bulb which controls the light. (Commercial fluorescent lighting usually has the ballast built into the fixture instead of attached to the tube, but they work the same way).

Fluorescent lighting is one type of "energy-saving" bulbs, although it's not the only kind. Other types of energy saving bulbs are LEDs (newer, more expensive than CFLs but even more efficient). Halogens are sometimes considered "energy efficient", though they're only marginally better than old-fashioned incandescents.

You might contact the manufacturer and find out what exactly is the problem with fluorescent lights. It's possible the ballasts create some electrical "noise" that the smoke alarm doesn't like. Or maybe the alarm sends a trickle of current through the fixtures which is not noticeable for incandescents but can cause fluorescent or LED bulbs to glow slightly. See also Why does using a dimmer with this ceiling fan and lights cause energy saving bulbs to flicker? and LED lights stay on, even when switch is off .

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The main problem seems to be electrical noise on the circuit. I can see how a fluorescent tube starting can generate this noise, but would a CFL really do the same? –  adrianbanks Feb 18 at 21:20
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CFLs are identical to commercial-style fluorescent tubing except smaller. Perhaps they're not large enough to be a problem, but you'd have to contact the manufacturer. –  Henry Jackson Feb 18 at 21:48
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It may also have to do with how the bulbs behave as they age. The reason tube fluorescents fail is because the gas becomes rarefied over time as it bombards the electrodes, the electrodes throw off metal, and that traps gas particles between the metal particles and the glass; that is why the tubes turn black near the ends. As the gas rarefies, there is more sporadic arcing. I don't know if that is a problem with CFLs as well, but we will all find out in a few years.

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It's a problem with CFLs. Terrible unreliable things, once Made In China really kicked in to lower the (initial) cost. –  Bryce Feb 19 at 21:26
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