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Advantages
- Low initial cost
- Low fixture cost
- Simple installation
- Inexpensive to dim
- All-weather operation
- High CRI
Disadvantages
- Voltage sensitive
- Lowest efficacy
- Short life
- Heat
Advantages
- Whiter light than incandescent
- Excellent lumen maintenance
- Longer life than incandescent
- More efficient than incandescent
Disadvantages
- More costly than incandescent
Advantages
- High efficacy
- Very good color
- Wide range of colors
- Wide range of wattages
- Good lumen maintenance
- Long life
Disadvantages
- Temperature effects
- Requires a ballast
- Light control
Advantages
- Good for landscape lighting
- Long life
- All-weather operation
Disadvantages
- Lowest HID efficacy
- Poor lumen maintenance
- Poor color
- Requires a ballast
- Restrike time
Advantages
- Highest efficacy
- Long life
- Universal burning position
- Range of wattages
- Good lumen maintenance
- All-temperature operation
Disadvantages
- Color
- Requires a ballast
- Cycling (standard lamp)
Advantages
- High efficacy
- Good color
- Good lumen maintenance
- Wide range of wattages
- Medium-long life
- All-temperature operation
Disadvantages
- Color shift
- Hot restrike time
- Requires a ballast
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The basic design of the incandescent lamp has not
changed much since the late 1800s, when Thomas
Alva Edison successfully produced the first operational
electric light bulb. These are the must-know
fundamental facts about incandescent lamps and
the alternative choices that are available today.
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TYPICAL SHAPES
The size and shape of a lamp’s bulb are designated by a letter(s) and a number.
The letter specifies the shape of the bulb and the number indicates the maximum
diameter in 1/8-inch increments. Example: A G40 is a globe shape which
is 5 inches in diameter.
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Just as a piece of metal being blacksmithed
or the molten glass at the end
of a blower’s rod heats to a brilliant glow,
so does the filament of an incandescent
lamp. The difference is that electricity
is used to heat the filament instead of fire.
This phenomenon is known as incandescence.
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THE FILAMENT
Incandescent lamp filaments are made
of tungsten. Tungsten is a metal that can
operate at very high temperatures without
evaporating too quickly and resulting in
early lamp failure. Incandescent filaments
only convert about 10 percent of the
energy used into visible light, so it is
necessary to use a material that can
withstand extremely high temperatures.
Most lamps use a coiled
filament design, which has been
found to be stronger and
deliver better performance.
THE GLASS BULB
The filament inside an
incandescent lamp must be
protected so that oxygen does
not reach it and cause it to
evaporate on contact. Most
incandescent lamps are either
vacuum-sealed or gas-filled. It
was discovered in the early
1900s that the introduction
of gas inside the bulb, or
envelope, created a pressure
against the filament. This
pressure allowed the filament
to burn hotter and last
longer. Most gas-filled
incandescent lamps today
use a mixture of argon
and nitrogen gases.
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Rated Voltage: The lamp’s filament
is designed to operate within a specific
voltage range in order for it to deliver
its intended light output. Lamps that are
burned at voltages higher than their rating
will result in higher wattage, efficacy
(lumens per watt) and lumens. Lamps
operated below their rated voltage will
significantly increase their life while
reducing their wattage, efficacy and
lumen output.
Lumen Maintenance: As the filament
of an incandescent lamp burns, the
tungsten is slowly evaporating and
depositing itself on the interior wall of
the bulb. This creates the black coating
seen after a bulb has been in use for
a while. Additionally, as the filament
evaporates, the lumen output decreases
until it reaches the end of its life when
the wire breaks. It is recommended that
a "group replacement" or relamping is
conducted once a number of lamps
have failed or a noticeable decrease in
light output has taken place.
Burning Position: For the most part,
incandescent lamps can be burned
in any position. However, take note
and observe a lamp manufacturer’s
recommendations for use.
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Screw-type bases used on incandescent lamps consist
of three components: the threaded screw section, the
glass insulation ring and the contact disc. The lead
wires which exit the glass bulb of the lamp are
attached to the base at two points. One wire is soldered
to the bottom of the contact disc and the other
to the top edge of the screw section. The glass ring
acts as an insulation barrier between the two points.
This assembly completes the circuit and the lamp is
electrified once the base is screwed into a socket
and the contact disc touches
the center point of the socket.
The base itself has nothing to do
with the seal of the bulb; it is a
separate part of the lamp that is
attached with cement. Typically,
bases are made from aluminum
or brass. Brass bases tend to perform
best due to their compatibility
with most socket materials.
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ASK THE
EXPERTS
Question:
What are some alternatives to standard incandescent lamps, and what applications are best suited for these alternatives?
Joe Rey-Barreau: The most common alternatives are
halogen and compact fluorescent light sources. Both are
available in a variety of shapes and with bases which can
be installed in standard sockets.
Halogen light sources are a type of incandescent technology
where a halogen gas has been inserted into the
bulb enclosure. This creates a whiter light than standard
incandescent, and provides for a longer operating life.
Halogen sources are excellent for use in recessed
downlights (or "cans"), track lighting and accent lighting.
The light produced by halogen sources is more vibrant
than incandescent and is ideal for spaces such as
kitchens and corridors. Bulb shapes available in
halogen, such as PAR lamps, provide excellent task
lighting from tall ceilings.
Compact fluorescent lamps are miniature versions of
the larger fluorescent bulbs used in offices and schools.
These new sources, however, are designed to provide
an excellent quality of light that is equal to or greater in
color rendering capability than incandescent.
There are compact fluorescent bulb shapes that can
be used to replace incandescent bulbs in recessed cans,
and table and floor lamps. They are also excellent for
general lighting, and are three to four times more efficient
than incandescent sources. They have a rated life of
approximately 10,000 hours compared with 1,000 to
2,000 hours for incandescent sources. Ideal applications
would be general lighting in kitchens, bathrooms, closets,
utility rooms, and in table and floor lamps.
Joe Rey-Barreau,
AIA, IES, CSI, is an Associate
Professor at the University of
Kentucky. He is a seasoned
lighting expert and educator,
leading seminars for the
American Lighting Assn.
(ALA) and others.
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