Chapter 3 Introduction to Basic Electrical Circuit Materials 67
usually manufactured in a spiral shape, such as that
shown in Figure 3-26. The strobe lamp operates by dis-
charging a high dc voltage directly through the tube.
What is observed is the electrical arc flashing through the
tube. Sometimes there are exciters placed along the
length of the tube to help attract the electrons through the
long tube. Exciters are charged lengths of wire that assist
the arc along the length of the glass tube. Strobes are
capable of producing flashes of such great intensity that
they can be used for airfield approach systems. The flash
of a strobe can generate an excess of 50,000 watts and can
be observed at distances greater than ten miles during the
light of day.
Lumen
Most people rate lighting brightness in wattage
because they are familiar with the incandescent light.
This is misleading. The amount of light produced by a
lamp is rated in candelas or lumens. The candela is based
upon the amount of light generated by one candle. The
lumen is the term used to measure the amount of light
generated by lighting systems. Look at Figure 3-27 to see
an illustration comparing the candela and lumen. A can-
dela will produce 12.57 lumens at a distance of one foot
from its center.
A 100 watt incandescent light (a typical value you
will find in your home) can produce as much as 4000
lumens of light. The chart that follows shows a compari-
son of light intensities. Lumens per watt (lpw) gives the
amount of light produced for each watt of energy used.
The higher the lpw, the more light you receive for each
watt of electricity.
Edison’s first lamp 1.4 lpw
Incandescent lamps 10–40 lpw
Fluorescent lamps 35–100 lpw
Halogen lamps 20–45 lpw
Mercury vapor lamps 50–60 lpw
Metal halide lamps 80–125 lpw
High-pressure sodium lamps 100–140 lpw
Review Questions for Section 3.4
1. What type of lamp was invented first?
2. Give several examples of electrical discharge lamps.
3. What lamp provides the most economical lighting
based on the amount of electricity used to create
the light?
4. Explain how a gas like neon becomes a conductor.
5. How is light intensity measured?
3.5 RESISTORS
One of the most common components encountered
in the study of electronics is the resistor. The resistor is
used to create desirable voltage drops and limit current
values in electronic circuitry. Figure 3-28 shows several
molded composition, fixed resistors. They are manufac-
tured in many sizes and shapes. The schematic symbol for
a fixed resistor is also shown.
Arc tube
Electrode
Porcelain base
Connection pins
Small strobe
Large strobe
Figure 3-26. Two types of strobe lamps.
1 sq. ft. equals
1 lumen
12.57 sq. ft.
surface area
1 foot radius
Fig 3-27. One candela will light a sphere with a total
surface area of 12.57 square feet.