You can't rule it out just yet. One of the most troublesome lamp-failure complaints that I ever got involved in (as a lighting engineer) involved just such a situation. The problem was a dining room chandelier with several lamps and it seemed to eat lamps. We tried dimmers, different lamps, electrical checks, etc. Nothing changed. Lamps failed almost daily. Then one evening we were sitting in the dining room and there was a great thump overhead and one of the lamps failed. Turned out that the kids' room was up there and it was the one of the kids jumping off the top level of the bunk bed. Bulbs with long thin filaments are particularly sensitive to what the lamp companies call "hot shock" and these poor lamps were getting a regular dose.
Anybody clumping around in the bathroom upstairs on a regular basis?
Your voltage and vibration causes for unusually short incandescent bulb life are correct; but heat and on/off cycles are not. The little bit of extra heat in a tight fixture makes no difference to a bulb filament which is operating at 3373 degrees C. For heat to affect bulb life, you have to either have enough heat to melt the glass, crack the internal glass seal or destroy the lamp basing cement. Think about incandescent bulbs in ovens and other high-temperature applications. There's nothing special about them.
On/off operation might affect bulb life a bit when the bulb is old; but not when the bulb is new. If on/off made a difference, we wouldn't see flashing sign lamps on theater marquees.
According to light bulb test data in the lighting literature, turning a bulb on and off has no effect during most of the bulb life. It is only when the bulb gets older and the filament starts to crystallize and get brittle that on/off makes a difference and why bulbs often fail when turned on due to the current surge and rapid heating. Old bulbs are also more sensitive to shock and vibration -- the brittle filament again.
Tests with bulbs left on and with bulbs on/off cycled when corrected for burning time showed little difference in life.
The above are long-held notions, maybe "urban legends", but the data don't confirm that heat or on/off cycling shorten incandescent bulb life. The references are in the Illuminating Engineering Society of North America Handbook, 9th. Ed. Chapter 6.
I pulled the fixture part down, but not out. The fixture (the part the light bulb screws into, right?) is wired directly to the junction box on the can somewhere in the ceiling. The wires leave the fixture and go out of the can to the junction box. The only thing on the wires was a piece of small black plastic (1/4" by 1/2") clamped on the hot wire. Couldn't see any writing on it.
I did go to Home Depot and got a 30W bulb to replace the long string of recently defunct 50W bulbs. The can does say that it will take a 50W R20.
Doesn't mean they last forever, though. :-) But they *do* have a much longer life than incandescent bulbs.
Yep. Same light output, with a *lot* less heat - which means that they use a lot less electricity, too, about 75% less.
The lifespan is going to be about five or six times as long as an incandescent lamp. If you're paying more than $4 each for your incandescents, the CF is a better buy *solely* on the basis of the cost of the lamps. When you figure in the savings in electricity costs over the life of the bulb, the CF is a *huge* money saver.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
Then why are special bulbs manufactured for those applications?
Yes, bulb filaments operate at very high temperatures, but the overall heat buildup for the bulb as a whole has a design limit. Exceed that limit, whithout exceeding limits that would cause a fire or do other damage, and you will see a decrease in bulb life.
It is stress, but generally has little effect on a newer bulb.
True, but what is the total hours of operation of these lamps and how does this compare to that of a bulb that is just left on?
All that said, a main point in my original post was that with the exception of vibrations, it is not likely that any one factor could reduce the life of a bulb nearly as much as the original poster was experiencing.
The only thing different about oven bulbs is that they have high-temperature basing cement so the base won't come apart and stick in the socket when the bulb is replaced. They may also have a a smaller glass envelope than similar wattage lamps made for general lighting service.
As I said, that's a widely-held opinion, but the tests reported in lighting journals, papers, etc. don't confirm that bulb life is reduced until the glass softens or a seal cracks and lets in air. That's not likely to happen in a situation where the fixture just seems to be hot to the touch even if there's some smoking or deterioration of the fixture finishes.
That's with the total "on" time taken into account.
Agree. There's something else going on here. It sure sounds like poor lamp quality and I'd like to see what happens when the OP tries another brand or type of bulb.
Do let us know how the 30W is doing. Also, try the 50W Halogen PAR (flood) lamp. HD has those too. If you did indeed get some faulty 50W R20s, I hope that you saved them and the packaging so you can take them back. If HD won't do anything, send them to the manufacturer. Likely you will at least get replacements and maybe a few extra.
Please note some things about using compact fluorescents in recessed ceiling fixtures, downlights, etc:
Compact fluorescents produce more non-radiant heat than incandescents of similar wattage, although usually less than that of incandescents of same light output. For example, a 42 watt compact fluorescent makes the fixture hotter than a 60 watt incandescent does, although not as hot as a 150 watt incandescent that the 42 watt CF approximates in light output.
Compact fluorescents do not take temperature extremes as well as incandescents do. Excessive heat can reduce life, dim them, and adversely affect their color and color rendering properties.
Many compact fluorescents are not even rated for use in recessed ceiling fixtures. Two that I have known to be rated for use in recessed ceiling fixtures are the Philips SLS 15 and 20 watt, and notably not higher wattages of this product line. (It's been a few years since I last checked.) The 15 and 20 watt SLS are available with snap-on R30 (3.75 inch diameter) and R40 (5 inch diameter) snap-on reflectors. The R40 version is not quite as good optically as an incandescent floodlight, and the R30 version is more severely compromised. The 20 watt has raw light output about that of 75 watt incandescents, although in floodlight duty with the R40 reflector may be closer to 60 watt unless the lamp count is large enough that you benefit from beams spreading into each other. The 15 watt version has raw light output about that of 60 watt incandescent.
As for other compact fluorescents in heat buildup situations: It appears to me that you usually get away with it with wattages up to 23 watts, and not with wattages of 24 watts or more. (For one thing, the 23 watt version of spiral units appears to me an improved version of 24 and
25 watt ones that did not do as well before.) I do expect that 26 watt and higher wattages will run into more heat trouble than wattages 23 watts or less. I do expect that most models 13 watts or less (with light output at most on a good day about that of a 60 watt "standard" incandescent) will run reasonably well in fixtures that accumulate heat.
Well, it's been 24 hours and a couple of off-on cycles and the 30W bulb still works. I may not seem like much but it has exceeded the lifespan of some other bulbs.
Bad bulbs are a possibility as I think the latest string of bulbs was a
6 pack from Costco. But they were Sylvania, not some no-name brand. If the 30W doesn't make muster then I'll look at a halogen PAR.
How about "reflector flood" compact fluorescents of size larger than R16 if they fit in your fixture?
The number after the R (or other bulb shape designation) in the USA usually means diameter in 1/8's of an inch. R16 is 2 inches in diameter, and R40 is 5 inches in diameter.
Look for larger sizes should they fit. Since the tubing of a compact fluorescent is bigger than an incandescent filament, you need a larger reflector to get the same optical properties. I do suggest seeing if the largest reflector size reflectorized compact fluorescent works for you.
Watch for poor contact in sockets that have previously experienced overtightening!
I remember seeing somewhere a recommendation to not screw in a lightbulb to an extent beyond 1/8 of a turn past the point of feeling like it made contact. Tightening past that point supposedly risks bending down the center contact in the socket.
Should you have a socket "damaged" by prior overtightening, then WITH POWER OFF, preferably with the appropriate breaker off: Pry the "cenhter contact" in the socket upwards with a screwdriver or whatever with just enough force to make it a little higher than it was recently, and "pat it down" with a light touch to make sure you actually bent it a little upwards.
The trouble is that lamps are made on such fast machinery today that if a machine gets out of adjustment, many bad lamps can be made very quickly. The quality manufacturers constantly test their products on the manufacturing line, so the chance of bad lamps getting out the door is small; but it does happen. At least with Sylvania lamps you'll likely get a response and some replacements if indeed the lamps are bad.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.