The Incandescent Light Bulb - Answers To Commonly Asked Questions.
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?"
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.
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.
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:
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 -
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.