Recessed Light Eating Bulbs

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I have a recessed light above my sink that is eating bulbs. About every 4th day the the R19 buld in the can burns out. I've checked the connections in the switch box and replaced the switch - to no avail. Any other suggestions? Thx -K2
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KTwo wrote:

Sounds like an overheating problem to me.
What's the wattage of the bulbs? Is it at or below the fixture's maximum wattage rating?
Are there vent openings in the can which are blocked by something above the fixture?
If all else fails, replace the switch with a slide type dimmer and rig something to keep the slider from moving all the way to "full".
HTH,
Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)
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Ya know, it might be a good time to do the calculations for what sized and wattage resistor would be needed to give a 10% drop in the supply voltage to the bulb, since an inline dimmer runs about 14 dollars at Home Depot.

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Jeff Wisnia wrote:

Jeff -
Overheating seems to be the general opinion. A number of the bulbs that have burned out to date where left for a couple of days and only burned out when one of my daughters turned the light off accidently when trying to turn the disposal off (the switches are in the same box). I'll try a smaller bulb. I don't think vibration is an issue. This light is above by kitchen sink, so there is no garbage disposal on the floor above it. The master bathroom is above it and I don't believe that is a large source of vibration.
Thx
-K2
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KTwo wrote: ...

..
Sounds like in an enclosed area w/ not enough air movement around the can...
I'd definitely go w/ the smaller wattage bulb and a 130V-rated would also extend life.
If at all possible I'd try to pull the can and make sure there isn't anything blocking the area around the fixture...
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SNIP
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?
TKM
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And whose fault is that? How often did you say they had to be replaced? ;-

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Michael Baugh wrote:

Some of them die in three or four days. They actually burn out faster than we can go through AA batteries! ;-)
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Good answer. I suggest the Hitachi unit.

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I'm sorry.
Steve B.
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050429 2145 - KTwo posted:

Sounds like a heat problem. Try one of the new fluorescent screw-in lamps. They run a lot cooler. One of the new "40 watt" equivalent lamps is labeled to draw 10 watts, and after about a minute, brightens up and seems to have a lumens equivalent of at least a 50 watt incandescent lamp.
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lamps.
labeled
a
Have a 3-60W bulb kitchen fixture that was failing bulbs well before they should have died--heat was the problem. Put in two 23 W new fluorescent screw-in lamps (equiv to 100 W) and what a difference. Runs much cooler with significantly more light. Left in one 60W bulb. Now have Lumens equal to 260W (vs. 180) while actually using 106W. Thinking of replacing the remaining 60W bulb except that it might be too bright now. <g> MLD
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MLD wrote:

My kitchen fixture is a 2-60W unit. Wound up replacing one, sometimes both each month. Switched to the fluorescent lamps over a year ago. Haven't touched it since.
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indago ( snipped-for-privacy@earthlink.net) said...

There are four things that can shorten the life of a bulb:
- heat - excessive turning on an off (manually or from a faulty switch) - vibration - voltage
When a bulb received more of any of these than it was designed for, its life shortens. For instance, roughly a 5% increase in voltage will reduce the life of a bulb by 50% (YMMV). So, a bulb rated at 1000 hours of operation at 120 volts will only operate for 500 hours at 126 volts, all else being equal.
Now, a bulb going after only four days (that's only 96 hours of operation, if it was burning continuous) sounds like something is REALLY excessive, and could even be a combination of things. In fact, a combination is likely here since the level of excess in any one factor needed to reduce the bulb's life to this would likely not go easily unnoticed.
Fixures have maximum bulb wattages based on their ability to properly dissipate heat. Using a bulb of higher wattage means the fixture will heat up too much and bulb life will be substantially reduced (in great excess, plastic parts will melt, or fire can be an issue). Alternatively, if vent holes are blocked or insulation is too close to the fixture, excessive heat can build up even with the correct wattage bulb (or even with a lower wattage bulb!)
Every time a bulb is turned on when it is cold, a great strain is placed on it. Cold filaments have a much lower resistance, so there is a brief surge of current greater than normally flows through it. You will likely experience a bulb blowing more often when you turn it on than having it just go while already lit due to this surge. Over the life of the bulb, each turn-on takes a little away from its life. Even when hot, it is better (for its lifespan) to leave it powered than to turn it off and on again. A faulty switch that has poor contacts, or even a faulty socket for the bulb can effectively be turning the bulb off and on again and thus be shortening its lifespan.
Vibration is a killer, and one that may have the quickest effect of killing a light bulb. If you ever experience a bulb blowing while it has been lit for sometime (as opposed to when you flip the switch described above), it is more likely due to vibration than to old age. This is the one factor I would suspect if there were only a single factor here.
I would check all of these, probably in this order: vibration, heat, faulty switch or socket, then voltage.
--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
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said...

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.
TKM
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<snip>

...but a bulb that is never shut off will last longer than a bulb going off and on. All my bulbs fail when turned on.
If a bulb is never cycled, its filament can get much weaker before it fails because it doesn't have to withstand any shock of heating or cooling.
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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.
TKM
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TKM ( snipped-for-privacy@no.net) said...

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.
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Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
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said...

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.
TKM
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indago wrote:

I had thought about compact flourescent (CF), but for another reason. I was thinking that since CF don't have a filament that there's nothing to burn out. Hadn't thought about it from the heat angle. I've looked and have only found one source (on the web or in a store) for CF R16 bulbs - and they're $20/ea. Ouch. Thx -K2
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