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One of my lightbulbs went out a few days ago and I was replacing it today. I found to my surprise that the base was yellowing for no apparent reason.

I found this article online: http://www.montgomerynews.com/articles/2012/10/13/springford_reporter_valley_item/news/doc5075ce95acf4f692783257.txt

It mentions that CFL lightbulbs shouldn't be used in enclosed/contained fixture, or risk the hazard of fire:

CFLS cannot be used in lighting units where the base of the CFL is encased or enclosed. “The key is letting air around” the base of the CFL bulbs, Lengel said. That means track lighting, recessed lighting and any fixture that encloses the CFL bulb is not safe to have a CFL bulb in.

One sign of a near fire as a result of improper CFL use is when the base of the CFL bulb is turning brown.

Here are some images:

Browning

In the picture above, you can see the browning.

Bulb

In the picture above, you can see the lightbulb information.

Finally, here is a shot (with the light turned out for contrast) of the fixture (there are two bulbs inside):

fixture

I would like to know if the lightbulb really is a fire hazard. If I was wrong in assuming that the bulb is not CFL, would it be a fire hazard if I did place a CFL (or two) in there?

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  • Mmm, the beautiful smell of CFL electronic death in the morning. It's a smell I equate to a GE radio my mom had that left a burnt streak on her desk, back when I was a kid. The power supplies were defective, would short out and burn the electronics inside. Thankfully, no paper was nearby. Every time a CFL burns out, I have a near panic attack over something electronic having caught fire. Convert to LEDs, Phillips are producing them as cheaply as CFLs now. Nobody should have to get used to that smell being the normal failure of a lighting device. – Fiasco Labs Jun 27 '15 at 16:35
  • @Fiasco Thank you, I will talk to my dad about getting them. – xTrollxDudex Jun 27 '15 at 16:41
  • Note that some LEDs specify that they are not suited for enclosed fixtures; check the label before you buy. – TomG Jun 27 '15 at 21:50
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A compact florescent (CFL) definitely heats up and needs to have room to dissipate that heat.

It is not nearly as hot (25–33%) as an equivalently bright incandescent, but the radiation pattern is different too. An incandescent has most of its heat coming out the bulb with only a small proportion from near the narrow base. A CFL has electronics in its base and those are responsible for a good amount of the bulb's heat.

The different heat pattern would explain why an enclosed base of a CFL would get crispy hot. If that were combined with stagnant air and warm ambient temperatures then yes, it could be a fire hazard.

However, your pictured light fixture probably does not confine the bulb's bases and was made for—what? 225 watts of incandescents? It should be fine for three 40 watt CFLs.

Do this experiment: fill it full of CFLs at or above the wattage you'd want to run. Close the cover and turn it on for at least 20 minutes. Take the cover off and feel inside. If anything is too hot to touch (120 °F/ 50 °C or greater), then it probably is not safe. If parts are warm to the touch but not verging on painful, it is most likely fine.

LED bulbs would be completely safe.

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  • Very hot. My dad can grip it for a few seconds but mentions that it is "very hot to the touch". I personally can't (my fingers aren't the toughest...). It's unlikely to be over 100 though. The airflow in my room is very good as there is plenty of wind during the morning and throughout most of the day. Ambient air temperatures are in the 70s due to the heat wave in this region. Is that a CFL bulb though? I'm not exactly an expert and I threw the box away a while ago. – xTrollxDudex Jun 27 '15 at 7:50
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    @xTrollxDudex: Yes, the bulb in the photos is a CFL. – wallyk Jun 27 '15 at 8:16
  • Many LED bulbs have similar issues with heat from the electronics, actually. Heatsinking is the bane of LED bulb design. – Ecnerwal Jun 27 '15 at 11:25
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    Also, it's a sign of improper phosphor coating at the base of the bulb. CFLs produce light by converting Ultra-Violet to visible light by irradiating a layer of rare earth oxides (phospors) which then emit light in the visible spectrum. If the phosphor coating is not dense enough, the lamp will emit ultraviolet. I've seen these cheap lamps where the tube ends are transparent, if you see this in a brand, quit buying them. UV will react with any material near it causing the yellowing you see. You don't want eye-damage in your future. – Fiasco Labs Jun 27 '15 at 16:29

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