"Calvin Henry-Cotnam" wrote in message
...
indago ) said...
050429 2145 - KTwo posted:
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?
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.
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."
- Napoleon
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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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