Copyright Goodheart-Willcox Co., Inc.
242 Engineering Fundamentals
Light-Emitting Diode (LED) Lamps
Light-emitting diode (LED) lamps are
extremely effi cient lamps that create light by
wiring semiconductor material in a forward
biased position. Forward bias is achieved by
wiring the negative side of the power supply to
the negative (cathode) side of the diode and the
positive side of the power supply to the positive
(anode) side of the diode. A forward biased direct
current is passed through a semiconductor mate-
rial inside the LED casing, and light is emitted.
Since the 1960s, LEDs have been used as indicator
lights and in seven-segment displays on devices
like digital clocks. More recently, as the technol-
ogy has advanced, they have been used in traf-
fi c lights, automobile lights, and fl ashlights. LED
lamps are inexpensive, extremely effi cient, and
long lasting. Their effi ciency and reliability result
from the fact that they do not create heat like
incandescent bulbs. See Figure 11-26.
Going Green
Compact Fluorescent Lamps (CFLs)
CFLs are good for our environment because
they save energy. If less electricity is used, less
electricity needs to be generated. Electrical gen-
eration stations that burn fossil fuels contribute to
greenhouse gases. Using less electricity means
burning less fossil fuels and emitting less green-
house gases.
The United States Environmental Protection
Agency (EPA) recommends that every household
replace their five most commonly used lights with
Energy Star qualified CFLs. This simple step would
decrease greenhouse gases equal to that created by
about 10 million cars.
CFLs contain a very small amount of mercury.
For this reason, it is best to recycle CFLs rather than
throwing them away in the trash. Many waste haulers,
power companies, and stores offer CFL recycling.
There are also programs that allow you to mail them
to a recycler for a fee. Because of the mercury, spe-
cial precautions must be taken if a CFL breaks.
New US federal lighting standards require
lightbulbs to use about 25% less energy. This
effectively means traditional incandescent bulbs
will no longer be made or sold except for specialty
applications. High-efficiency halogen incandes-
cent bulbs meet the new requirements. CFLs and
LED bulbs are the most common replacement for
traditional incandescent bulbs. Linear fluorescent
tubes like those commonly found in schools are
also required to become more energy efficient. The
standards also require that bulbs be advertised
by lumens of light emitted rather than wattage, or
power consumed. Lumens are the measure of the
visible light emitted by a bulb.
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Cathode Anode
Electrons
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Forward Bias
Holes
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Goodheart-Willcox Publisher
Figure 11-26. 
A forward biased direct current can pass through
a semiconductor material inside an LED casing to
produce light.