66 Fundamentals of Electricity and Electronics
Neon lamp
A neon lamp consists of two electrodes inserted in
the ends of a long glass tube. The tube is often heated
and shaped into words or pictures for commercial
applications, Figure 3-25. After being shaped to achieve
a desired effect, the tube is filled with neon gas.
A neon light transformer is used to produce a high
voltage (10,000 volts or more), which is needed to create
a current through the neon gas. Because of the high volt-
age present, special high voltage insulation is used to
insulate the conductors. After the light is energized, the
neon tube will glow. Parts of the tube may be darkened
out by black paint to achieve varied designs. To create a
variety of colors, other gases such as argon and helium
can be used. Although these lamps are filled with gases
other than neon, they are often refered to as “neon lamps”
out of custom.
Glow lamp
The glow lamp is very similar in construction to a
neon lamp. It consists of two electrodes inside a short
glass tube filled with neon or argon. The electrodes in a
glow lamp are quite close in comparison to the neon light.
Consequently, a glow lamp does not require the same
high voltages required in typical neon signs.
Strobe lamp
A strobe lamp may vary from a very short to a very
long piece of glass tubing. The long strobe tubes are
Darkened areas will
not be seen when
energized.
High voltage
connection
Glass tube
filled with neon
High voltage cable
Transformer
Ceramic
insulator
Figure 3-25. For neon lighting, a glass tube is filled with
neon gas. Then an electrical charge, in excess of 10,000
volts, is passed through the tube.
Outer tube
Starting electrode
Reflector
Base
Bottom electrode
Arc tube
Top electrode
Figure 3-24. Mercury vapor lamp.
CFLs are designed for use with both AC and DC sources.
The DC type is used for recreational vehicles and portable
lighting that runs on batteries.
Mercury vapor lamp
Figure 3-24 shows the construction of a typical mer-
cury vapor lamp. It consists of two electrodes connected
at opposite ends of the arc tube. The arc tube contains a
small amount of mercury and argon gas. When the lamp
is energized, the starting electrode generates heat to
vaporize the mercury and ionize the argon. After consid-
erable time, the starting electrode opens allowing current
to flow through the arc tube. The disadvantage of this
type of lamp is the long delay required when starting or
when the power has been temporarily interrupted.
Compact
fluorescent tube
Ballast
Standard
screw base
Figure 3-23. CFLs come in different physical shapes. One
of the most popular is the spiral shape. The ballast built into
the large base fits a standard incandescent lamp socket.