When it is colder outside, I noticed that the CFLs in my house and the fluorescent lights in my garage take longer to come on and get bright. Sometimes they flicker more. I am in Florida so coldest is probably 30-40 degrees in the Winter. Why does this occur? CFLs are in a standard outlet. Fluorescents are in an older ballast.

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    Add "Why do...?" to your title to make your question a ... uhh ... question. – Jay Bazuzi Oct 30 '10 at 16:51
  • @Jay: I've been on the SE network for some time now and the titles do not have to have the question in them.. Browse SO right now and I'm sure you will see the same thing. – Brian Oct 30 '10 at 23:06
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    Sure, but your title is a statement of fact. I can't tell if you're just curious why, or whether there's a way to make them start up faster, or whether there are some models that don't have that problem. I like your question, and I am interested in the answer; this is just a minor improvement. – Jay Bazuzi Oct 31 '10 at 2:52
  • @Jay: I know but the way your statement is worded, it comes off as pedantic and as a know-it-all. It puts people on the defensive. – Brian Oct 31 '10 at 17:22

When turned off, the mercury in the fluorescent tube condenses on the inside surface of the tube. In order to emit light, the mercury must evaporate and form a vapor as the conductive path between the ends of the tube. The colder the bulb is to begin with, the longer it takes for all the mercury to evaporate, and for the light to reach full brightness.

This also explains why fluorescent lights get dimmer as they age: there is a small leakage of mercury from the tube during its lifetime, so there is less mercury vapor in the tube, so less light produced.

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