Chapter 3 Introduction to Basic Electrical Circuit Materials 65
the mercury inside the tube. Once the mercury has been
vaporized, electrons flow along the mercury vapor.
Ultraviolet light is produced inside the tube. The
ultraviolet light strikes the phosphor coating and causes it
to glow. This produces the familiar phosphorous light. A
ballast is used to limit current inside the tube. The ballast
consists of many turns of fine wire. The ballast is also
used to produce a higher than usual voltage, which is
applied to the filaments in the ends of the tube.
An older style of fluorescent lighting used starters in
the circuitry between the ballast and lamp. The purpose
of the starter was to allow the filament inside the lamp to
conduct and produce the necessary heat to vaporize the
mercury. Once this was accomplished, the starter would
open and cease the heating action of the filament. Newer
fluorescent lamps incorporate a device in the end of the
tube that replaces the need for a starter.
Compact fluorescent lamp
Compact fluorescent lamps (CFLs) are special
florescent lamps designed to screw into a standard incan-
descent lamp. CFLs are much more efficient than incan-
descent lamps. For example, a traditional incandescent
60 watt lamp can be replaced with an 11 to 15 watt CFL
and produce the same amount of light using 1/4 of the
electrical energy. Temperature is another way CFLs are
cost effective. An incandescent lamp gives much more
heat than a CFL. Replacing incandescent lamps with
CFLs can reduce the cost of air conditioning.
A typical spiral-type CFL is shown in Figure 3-23.
The large base of the bulb contains the ballast that is
required for fluorescent lamps. The initial cost of the CFL
is higher when compared to an incandescent lamp, but the
savings are realized after approximately 500 hours of use.
Figure 3-20. An incandescent lamp consists of a tungsten
filament inside a glass envelope filled with an inert gas.
Tungsten
filament
Glass filament
support
Filament
connections
Base
Inert gas
Glass
envelope
Infrared rays
Tungsten filament
Figure 3-21. Halogen—IR uses a coating inside the tube
that causes infrared rays to be reflected back toward the
filament.
Gas inside tube
usually argon
Pin base
Glass tube coated
with phosphor
Filament
Figure 3-22. Fluorescent lamp.
returns the boiled off tungsten filament particles back to
the filament, thus causing the filaments to last longer,
Figure 3-21.
Discharge Lamp Principles
A discharge lamp operates differently from an
incandescent lamp. A discharge lamp produces light by
energizing a gas such as argon, neon, helium, or a vapor
of mercury or sodium. The gas or vapor is ionized by the
electrical pressure and will glow, thus emitting light. A
discharge lamp can easily produce 20 times more light
than a conventional filament bulb, while using the same
amount of electrical energy. Descriptions of several types
of discharge lamps follow.
Fluorescent lamp
The fluorescent lamp consists of a long glass tube
coated on the inside with a phosphor. See Figure 3-22. A
filament or electrode is inserted at each end of the tube.
The air is removed from the tube, and then it is filled with
an inert gas and a small amount of mercury. When the
tube is energized, the filaments at the end will glow.
However, the filaments do not provide very much light.
The filaments are used to produce heat, which vaporizes