Enclosed fixtures?

My porchlight burned out and I went to Home Depot to get a replacement bulb. The previous one was a sort of torpedo-shaped fluorescent arrangement branded "Lights of America" and, as I recall (it's been several years), rated for outdoor use. The Home Depot fella told me I was imagining a light specifically rated for outdoor use -- that any fluorescent was fine, and pointed to a shelf. I bought a small twirly-tube thing that cites a "minimum starting temperature" of -20F. The front panel says "Usages: suitable for totally enclosed fixtures" with 2 little pictures of a lamp and a ceiling fan with lights.The porch lamp is not "totally enclosed" enough to prevent a rain of dead moths from falling on my face as I removed the plastic panel bottom enclosure. It's outdoors on the porch ceiling, not "enclosed" in the house.
What does "totally enclosed" mean?
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Frogleg wrote:

enclosed fixture.....
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Totally enclosed light fixtures build up more heat that open ones do. So you need a bulb that will withstand the higher temps. If your fixture is on the porch ceiling with a plastic enclosure, then you really don't have to have a buld rated for exterior use since it won't be getting wet.
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wrote:

I see I haven't made myself clear. The package for the new fluorescent 'bulb' says "Usages: Suitable for totally enclosed fixtures" with one small drawing of a table lamp and another of a ceiling fan with light cluster. The product is made in China, which may contribute to the terminology confusion. Actually, the "...totally enclosed" is *under* the little drawings, so perhaps it means that as well as using in 'open' fixtures (like lamp and light cluster), it is *additionally* suitable for totally enclosed situations. Hmmm.
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