Introduction to Fluorescent and Incandescent Light Fixtures Inspection

1- Introduction

In this course you will learn:

  • How to inspect fluorescent lighting fixtures and incandescent lighting fixtures (Fig.1),
  • How to identify the correct fixture to be inspected,
  • How to verify that the fixture is properly installed,
  • How to document your inspection results.

This course will reference the National Electric Code (NEC) and Underwriters Laboratory (UL) documents.

Fig.1: Fluorescent and Incandescent Lighting Fixtures

2- Verify that the Correct Fixture is being inspected

First: Incandescent Light Fixtures

  • The incandescent lamp consists of a filament which is a highly refractory conductor mounted in a transparent or translucent glass bulb and provided with a suitable electrically connecting base. The filament is heated by the passage of an electric current through it to such a high temperature that it becomes incandescent and emits light. The older types of bulbs had the air inside of them removed. The modern lamps today have this space filled with an inert transparent gas such as nitrogen.

  • (Fig.2) shows porcelain, single lamp, incandescent light fixture and a lamp. When the lamp is attached, the fixture operates as a common unit. The incandescent light fixture can be designed to hold one of several types of lamps. This type of fixture is used with a screw—type lamp base or cap. 

Fig.2: A Standard Incandescent Light Fixture and a Lamp

  • The incandescent lamp is widely used in many applications and often seen in the home. The life expectancy of an incandescent lamp is much less than a fluorescent lamp. The incandescent lamp is identified by the filament. The filament is made from a metallic material called tungsten. (Fig.3) shows a heavy duty lamp used for construction work.

Fig.3: Basic Construction of a Standard Incandescent Lamp

Classification of incandescent Lamps
Incandescent lamps can be classified in six different ways, according to:

  1. The class of lamp,
  2. The type of the base,
  3. The shape of the bulb,
  4. The type of filament,
  5. The finish of the bulb,
  6. The type of service.

1- Class of lamp

  • Lamps are classified as either Type B or Type C. 
  • The Type B lamp is one in which all the air has been removed. 
  • The Type C is one which is gas-filled. Gas-filled lamps are the most widely used types.

2- The type of base

  • A number of different types of bases for incandescent lamps are in use (fig.4).

Fig.4: Standard Incandescent Lamp Bases

  • The medium base, used on general-service lamps of 300 watts and less, is the most common type. 
  • The mogul base is used for 300 watts and above.  
  • Other popular bases are the bayonet, candelabra, and intermediate bases are used on small size (miniature) lamps.

3- Shape of bulb

Incandescent lamps come in various shapes and sizes (fig.5), all designated by a letter or letters followed by a number. The letter is to identify the lamp's shape while the numerical designation is to identify the diameter of the lamp in an eighth of an inch. 

Fig.5: Standard Incandescent Lamp Shapes


Lamp model 60A19, means :

60: Wattage (60 W) 
A: Bulb shape 
19: Maximum bulb diameter, in eighths of an inch. (19 ÷ 8 = 2.38 in)
  • The most common shape for incandescent lamps and the one everyone knows is the A shape (A-19) - The A is only an arbitrary designation. 
  • The below table include the most used shape codes for Incandescent lamps.

Arbitrary (standard)
universal use for home lighting
Bulging reflector
for substitution of incandescent R lamps
Cone shape
used mostly for small appliances and indicator lamps
Elliptical reflector
for substitution of incandescent R lamps
decorative interior lighting
ornamental lighting and some floodlights
standard for streetcar and locomotive headlights
Parabolic aluminized
used in spotlight and floodlight reflector
lower wattage lamps - sign and decorative
showcase and appliance lighting

4- Bulb finishes

Incandescent bulbs can be finished in a variety of different ways. Some of the more popular ones are listed below:

  1. Clear,
  2. Inside-colored,
  3. Inside-frosted,
  4. Outside-colored,
  5. Silvered bowl,
  6. Colored-glass,
  7. White,
  8. Outside-coating,
  9. Daylight.

5- Type of filament

Several different types of filament structures are used (fig.6). The filament structure is designated by a letter or letters to indicate whether the wire is straight or coiled and by an arbitrary number sometimes followed by a letter to indicate the arrangement of the filament on the supports. Prefix letters include:

S =    straight; wire is straight or slightly corrugated
C =    coil; wire is wound into a helical coil or it may be deeply fluted.
CC = Coiled coils; wire is wound into a helical coil, and this coil wire is again wound into a helical coil.

Fig.6: Standard Incandescent Lamp Filaments 

The below table include the most Common Filament types for Incandescent lamps.

 Short, coiled filament requiring two supports.
 Short, coiled curbed filament requiring no support.
 Short, coiled filament requiring support.
 Short, double-coiled filament requiring support.
 Concentrated filament for small light sources.
 Short, coiled filament requiring little or no support.
 Short, double-coiled filament requiring few supports.
 Two short, coiled filaments requiring little or no support mounted one on top of the other.
 Long filament supported at the top for base up usage.
 Long filament supported at the top and at the base for universal usage.
 Coiled filament mounted in lamp axis. Can be extended like Lumiline lamps.
 Short, double-coiled filament mounted in the lamp axis.
 Two short, double-coiled filaments mounted in the lamp axis.
 Average length filament mounted in the lamp axis.
 Average length double-coiled filament mounted in the lamp axis.
 Average length, concentrated filament. Well supported, "M" Shape.
 Flat, very concentrated filament for projection equipment.
 Flat, very concentrated double-coiled filament for projection equipment.
 Long filament requiring more support than usual.

6- Type of service

Incandescent bulbs are manufactured for a wide range of services, most of which can be classified into three categories:

  • General lighting service: These are the most common bulbs used   for general lighting.
  • Special lighting service: This group includes the three-way bulbs, daylight lamps, and decorative lamps.
  • Miscellaneous lighting service: Street lighting, traffic-signal lamps,            and photographic lamps fall into this category. The overhead projector lamp is also included in this group.

In the next Article, I will explain Fluorescent Lighting Fixtures and its Components. Please keep following,

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