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Chapter 11 Electrical Engineering 241
Incandescent Lamps
As electrons fl ow through a conductor, they
create friction and, therefore, heat. Some conductors
can get very hot. This heat can be used to generate
light. An incandescent lamp creates light when the
current fl ow causes the tungsten fi lament to get so
hot that it glows. The tungsten fi lament is suspended
inside a glass globe. All of the air inside the globe is
removed because the oxygen would allow the fi la-
ment to burn. Sometimes the air is replaced with an
inert gas, such as argon. If there were oxygen inside
the globe, the fi lament would burn up due to the
heat. See Figure  11-24. Federal energy effi ciency
legislation has mandated traditional incandes-
cent bulbs be phased out in favor of more effi cient
devices, such as high-effi ciency incandescent, CFLs,
and LEDs, which are described below.
Gas Discharge Lamps
In gas discharge lamps, the glass inside the
globe is ionized. Electrons are released from their
bonds and are free to fl ow. This causes the gas to
glow and create light. Neon lamps are an example
of gas discharge lamps, but other gases are also
used. A resistor must be placed in series with the
light to limit current fl ow because the resistance of
the ionized glass is so low. Gas discharge lamps
can create the same amount of light as incandes-
cent lamps, using a fraction of the electricity.
Yegor Korzh/Shutterstock.com
Figure 11-24. 
This incandescent lamp uses a tungsten filament to
create heat, which generates light.
Fluorescent Lamps
Fluorescent lamps consist of a long glass tube
coated on the inside with phosphorous and fi lled
with an inert gas. There is also a small amount of
mercury. At each end of the tube, there is a fi la-
ment, which creates a small amount of heat to
vaporize the mercury. Passing electrical current
through the vaporized mercury produces ultra-
violet light, which is invisible to humans. The
ultraviolet light causes the phosphorous to glow,
creating the light we see. It is important to note
that fl uorescent lamps use much less electricity
than incandescent lamps because incandescent
lamps waste so much energy in the form of heat.
Compact Fluorescent Lamps
Compact fl uorescent lamps (CFLs) work on the
same principle as the fl uorescent lamps discussed
previously, but are designed to fi t into normal light
sockets. CFLs have been around for quite a while,
but recent technological advancements and concerns
about global climate change have made them more
popular. CFLs use about 75% less energy than
incandescent lamps and last up to ten times longer.
Figure 11-25 shows a compact fl uorescent bulb.
See Workbook Activity 11-11 to calculate the
cost savings of replacing a standard bulb
with a CFL.
Jonathan Vasata/Shutterstock.com
Figure 11-25. 
CFLs can be used to replace incandescent bulbs, using
less energy.