CFL bulbs and high temperatures

[CFL2009]

So we know that high temperatures will decrease the life of CFL's (I've read by 15-20%), but I had some questions related to how exactly temperature affects the bulbs.

1)[FONT=&quot] [/FONT]What part of the CFL fails due to high temperature? (the ballast or the tube?)
2)[FONT=&quot] [/FONT]Assuming an improper installation (upside down, in a recessed can, or inside an enclosure) where does most of the heat come from? The ballast or the tube?
3)[FONT=&quot] [/FONT]Could reflective material at the base of the tube keep heat away from the ballast and extend the life? (similar to reflector/spot CFL's?)
4)[FONT=&quot] [/FONT]How hot could the tube get before decreased life would be seen?

I'm researching light fixture designs and have found that most people are not aware of the tight temperature band for the cheap spirals that are selling like crazy right now. The advertised savings on the box from switching from incandescent bulbs assumes perfect conditions, but people are amazed when they fail early.

Comments welcome!

 

[jtr1962]

1)What part of the CFL fails due to high temperature? (the ballast or the tube?)

The ballast is generally a lot more sensitive to heat than the tube. Higher temperatures also affect tube life, but not to the same extent as ballast life.

2)Assuming an improper installation (upside down, in a recessed can, or inside an enclosure) where does most of the heat come from? The ballast or the tube?

By far most of the heat is from the tube. For most CFLs anywhere between 10% and 20% of the input power is wasted in the ballast. The rest (minus the percentage emitted as light ~20%) is lost in the tube.

3)Could reflective material at the base of the tube keep heat away from the ballast and extend the life? (similar to reflector/spot CFL's?)

No. The tube isn't a blackbody emitter. It emits very little infrared radiation, so reflective material wouldn't be very good here.

4)How hot could the tube get before decreased life would be seen?

The tube is made of gas, glass, and phosphors. The phosphor is the part most sensitive to degradation by heat. I'll guess anything up to maybe 100°C is OK but take that with a grain of salt. I don't know the exact answer.

I'm researching light fixture designs and have found that most people are not aware of the tight temperature band for the cheap spirals that are selling like crazy right now. The advertised savings on the box from switching from incandescent bulbs assumes perfect conditions, but people are amazed when they fail early.

They fail mostly because you really can't design decent ballast electronics for the price these things are selling for. Back when CFLs cost $20 and up they seemed to be more reliable. People complained about the price, so they made them less expensive. The old adage you get what you pay comes to mind here.

Another thing to add regarding CFLs is the fact that you're trying to shoehorn a technology into a form factor not really designed for it. Incandescent fixtures are designed to hold in heat due to the nature of their light source. No surprise then that designing CFLs which last is an expensive proposition. You're taking something which wants to be long and with a separate ballast, curling the tube into a spiral, and then putting the ballast in close proximity. And we're surprised they don't last? Frankly, I'm surprised they last as long as they do. There's a reason most CFLs are rated between 6,000 and 10,000 hours, while linear tubes are anywhere from 20,000 to 35,000 hours. Even in the best case, and if everything is made well, lifetime is going to be compromised. Truth is if you want to use fluorescents optimally, you need a purpose-designed fixture which takes either bi-pin CFLs or linear tubes. You can get CFLs which work well if you're willing to spend $15. However, I figure if a fixture takes a few lamps, then the quality CFLs are setting you back around what a replacement fixture will cost, and you'll be spending that much again every time you need to replace lamps. Might as well just drop the $$$ on a decent fluorescent fixture from the get go. In the long run your customers will be happier.

 

[CFL2009]

Excellent info, thanks! I agree that the packaging of CFL hardware seems to be a very difficult problem from the start.