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The Incandescent Light Bulb - Answers To Commonly Asked Questions.

By: Jonathan Z. Kremer

Many times I find myself answering the same questions over and over again about a particular electrical topic. One topic that probably surpasses the rest in frequency is the standard incandescent light bulb. This simple bulb seems to be the topic of discussion in almost any home I step into for a service call. "Why do my bulbs burn out so often?" "Why does the breaker jump when the bulb burns?" "Is there a better solution using the same light fixture?"

There is really not much to it once you know a few basic facts and principles.

The Basics

The incandescent bulb has a tungsten filament which is held up by a glass mount in the middle of the bulb, and then filled with an inert gas such as argon. This element lights up when power is applied and not only gives off light, but heat as well, very similar to a very small heating element. The incandescent bulb is not very energy-efficient, as only five to eight percent of the energy that goes into the fixture produces light, while the rest is dissipated as heat. The filament's temperature can reach over 2200 degrees Celsius, depending on the type and size of the bulb.

Due to the high temperature that the filament is operating at, some tungsten is always evaporating off the filament during use, causing the filament to thin out unevenly. The temperature becomes greater at these "thin spots", causing them to evaporate even quicker, and eventually, burn out.

Why do my bulbs burn out so quickly?

This can be caused by a number of things. Before thinking that you have a problem, it's good to make sure that your expectations are not excessive. Incandescent bulbs have an approximate life span of 700 - 1000 hours depending on the make and the wattage of the bulb. The cheaper bulbs will last even less time.

If the bulbs, all around your home, are burning out way too quickly, maybe you have excessive voltage coming from the Electric Company. You can bring in an electrician to check this out, but usually the Electric Company will not even try to correct the problem unless there is an unusually high voltage.

Other causes include:

  1. Using the wrong wattage bulb for the lamp.
  2. The lamp has some sort of cover which prevents the heat coming from the bulb to escape, causing the bulb to overheat.
  3. The bulb gets jolted while the element is hot, causing the filament to break. This can be caused by a door slamming, children playing with a ball, wind rocking a hanging fixture, people jumping or dancing on the floor above...etc.
  4. The use of "cheap" quality light bulbs.
  5. Bad connection either in socket or in connections.

Why do my light bulbs flicker?

The number one cause for flickering is a bad connection between the bulb and the bulb socket. This can usually be solved fairly easily, although sometimes the contacts of the socket are so corroded or broken that the whole socket must be replaced. For illustrated instructions as to how to troubleshoot this problem see:

Other causes for flickering include:

  1. A bad switch or dimmer.
  2. Some other bad electrical connection between the lamp and the main electrical panel.

Why is it that when I change a bulb, the new bulb doesn't work even though the bulb is good?

Same as flickering light - above.

Why do my bulbs burn out as soon as I put them on?

It is well known that a cold light bulb filament has less resistance than a hot one. When the filament in the bulb gets worn (see Basic above) it gets unevenly thin. When the switch is turned on to light the bulb, the filament can no longer hold the power surge that is flowing through it, due to it's cold state. It therefore burns out on the spot.

Why does my breaker jump when my bulb burns out? Sometimes the bulb explodes too.

When the filament in the bulb breaks, an arc sometimes forms, expanding across the entire broken filament. While drawing a few hundred amperes of current, the arc starts to get unstable and melts what is left of the filament, in a bright blue glow. This will usually cause the bulb to burst and the circuit breaker to trip. Most good quality bulbs have a small built-in fuse inside the base that will normally burn before your breaker has a chance to trip. Cheaper bulbs have poor quality control and no built-in fuse in the base.


  1. Always buy quality bulbs from reputable manufacturers. In Israel my favorite is Osram/Sylvania. Philips is also good. Cheap quality bulbs are more apt to burn out quicker and have a tendency to blow out the line circuit breaker when they arc.
  2. Make sure your bulb is screwed in properly, but do not over tighten.
  3. Replace incandescent bulbs with compact fluorescent lamps (CFLs) or LED lighting where possible. CFLs can last up to ten times longer (LEDS up to 85 times). CFLs provide the same amount of (light) lumens as standard incandescent bulbs, but use up to 75 percent less energy.

Jonathan Z. Kremer (better known as Yoni) is the proprietor of "Yoni - Electrical Design and Installations", a Maale Adumim (Israel) based business that has been serving primarily Jerusalem, Maale Adumim, and surrounding areas since 1989. We undertake various forms of electrical work including renovations, maintenance, installations, and repairs - encompassing the domestic (home), industrial and commercial arenas. We believe that our success tomorrow will be determined by how well we serve you today.

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