Why Light Bulbs Burn Out So Quickly

I've consolidated and edited the following comments from alt.home.repair. They're from Dan Dan Hicks <danhicks@ieee.org>, and others, including me.


"Geoff Aumaugher" <aumaugh@ibm.net> writes:

I am wondering if anyone could help me out with this problem. I am having problems with lightbulbs burning out in a matter of months. Does anyone know what the problem could be and how I could check it out. Thanks in advance.

The bulb package should have an average life expectancy printed on it. The typical light bulb is good for roughly 900 hours. At 10 hours a day that's three months. At 24 hours a day it's a little more than a month. If you have 25 bulbs in your house burning an average of three hours each day, a bulb will burn out every twelve days, on average.

If you compute the average life of your bulbs and discover it's clearly less than the manufacturer's rated life, then you may have:

  • You may have over-voltage in your house.  Occasionally this causes more serious problems.  You can get a cheap multimeter at Radio Shack. If the voltage is 125V or higher, talk to the power company about it.  7 or 8 extra volts on a 120V line will cut the bulb life expectancy in half.  If it's a slight over-voltage, you can buy special 125V or 130V bulbs, though sometimes they're hard to find.
  • Too high a wattage bulb in too small an enclosed fixture (such as a globe), the heat can't get out--the bulb burns too hot, leading to short bulb life.
  • Recessed lighting fixtures often get covered by attic insulation. This blocks the intended ventilation method--heat can build up around the bulb, causing short bulb life.
  • A vibration problem. Such as, bulbs under a heavily used stairway, on or near an out of balance bathroom or ceiling fan, or near a door that gets slammed, or kids upstairs jumping, etc. You can buy special shock resistant, also called "rough service" bulbs, for this situation, or try one of the new compact screw-in fluorescent bulbs.

Flickering. Intermittent electrical contact can cause flickering.  It's like turning the light on-and-off constantly, and will reduce bulb life.  It can be caused by a bad light socket, or a poor electrical connection somewhere in the wires leading to the light (most likely right at the fixture).  Flickering can cause the bad connection to get hot and possibly start a fire.  If you don't locate the cause of the flickering and it affects all or many lights, you could have a bad neutral connection -- a dangerous situation.  Another indication of a neutral problem; as larger appliances (washing machines/dish washers) cycle, lights will get quite noticeably brighter or dimmer (minor changes in intensity are normal).  If you suspect this problem have either the electric company or an electrician check it out.

Trivia Break

Most lights flicker all the time but you don't realize it because of a psychological phenomenon called 'flicker fusion frequency.' The flicker fusion frequency is usually about 25 hertz (cycles-per-second). A light that turns on-and-off (flickers) faster than 25 times per second will appear to be on, steady. Your home's 60 cycle AC turns on and off 120 times a second, though it is only off momentarily, it's increasing or decreasing the rest of the time. If you use a dimmer switch it turns the power to the light completely off for a while 120 times a second. Of course, incandescent lights don't have time to cool down to dark during these brief off times but, they dim and brighten. Early movies used too few frames per second, that's why they flicker. Whereas, later movies are frequent enough; so, though there are totally black moments between each frame, you don't see any flicker.

Note: The 25Hz is an ordinary/average value. It varies based on the brightness/intensity of the source and can go as high as 50-60Hz for very bright sources.

 

Some people sell 130 volt bulbs as 'long lasting.' If you have proper voltage, they will last longer, but they're not a good deal -- they cost more per unit of light overall.  Click here for an explanation.  If you want long lasting buy a compact fluorescent.  Not only will it last longer you'll probably save a little $$ too.

More Than You Ever Wanted To Know About Lights

 

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