Incandescent Lamp Specifications
All incandescent
lamps operate on the same basic principle: an electric current is forced
through a wire filament that resists the flow of electricity. As the current
fights the resistance, heat is generated. When the filament gets very hot, it
glows with "black body radiation" and becomes.
Introduction
Even the simply "light bulb" lamp has many variations.
Such lamps can be specified by their many characteristics:
Performance characteristics, such as:
- Voltage
- Wattage
- Brightness
- Color
- Lifetime
type and size of the base (electrical connector), which can be indicated
several ways:
common name (such as "candelabra")
diameter of the base in inch fractions
the letter "E" and the diameter of the base in millimeters (e.g. E26 is
a base 26mm in diameter)
size and shape of the glass envelope, which can be indicated several ways:
- An,
- e.g. A19
PARn,
- e.g. PAR38
Rn,
- e.g. R30
MR-n,
- e.g. MR-16
Gn,
- e.g. G30
Cn,
- e.g. C9
maximum overall length (often in inches)
For example, the common household "light bulb" in the United States uses an
E26 screw base, with an A19 envelope.
Performance Characteristics
Voltage
All incandescent lamps have a rated operating voltage.
- If you feed the lamp with electricity at a lower voltage, the lamp will be
dim, the light will be more yellow in color, and the lamp might last a little
longer.
- If you feed the lamp a voltage slightly higher than the rating, the light
will be brighter, whiter, and the lamp will not last as long as it should.
- If you give the lamp considerably more voltage than it is rated for, it
will fail, probably burning out in one brief flash of light.
Wattage
Wattage indicates the amount of power consumed by a
lamp.
Wattage is often used as a substitute for the brightness of a lamp, but it is
a poor substitute. Usually, a 100 Watt lamp will burn brighter than a 50 Watt
lamp. But just because the larger lamp is using twice as much power, doesn't
mean it is putting out twice as much light. It could be that the 100 Watt lamp
is very inefficient at turning electricity into light, and the 50 Watt lamp is
much more efficient.
Brightness
To find out how bright a lamp truly is, check the rating in
lumens.
 This panel is printed on a box of Philips lamps.
Color
Since filament lamps rely on incandescent
"black body radiation", their output is broad in spectrum. This is usually a
good thing when it comes to good color rendition. But if you want to approximate
daylight, you need to specify a lamp that outputs light more to the blue end of
the spectrum like a Tungsten Lamp.
Beam Pattern
A common "light bulb" broadcasts light in all directions.
Some lamps have built-in reflectors and/or lenses that let them throw a beam
with predictable characteristics.
Lifetime
The anticipated lifetime of a lamp can be quite important.
- Consider a light at the top of a high stairwell, where it is difficult to
replace the lamp. It might be worth an extra dollar for a long-lasting lamp,
so you don't have to get the ladder out again.
- Consider the lamp in a movie projector. If it burns out in the middle of a
show, patrons will be upset.
- Failure of an indicator lamp in a medical machine could mean the death of
a patient.
- Failure of an indicator lamp in an industrial safety application could
mean a new patient.
- One of the most common failures in old VCR's is the lamp that is used to
sense the end of the tape. The replacement lamp probably costs less than a
dollar, but the tech will have to charge a minimum service fee of $30 or so.
Lamp Base
The "base" of the lamp provides both mechanical attachment and
electrical connection.
Most incandescent lamps have screw
bases.
Automotive lamps tend not to use screw-base lamps because vibration can cause
them to unscrew themselves. Many automotive lamps use bayonet
bases or some form of
lugs
or blades.
Screw Base
Most incandescent lamps have screw bases, with a right hand
thread.
 Different sizes are distinguished by the outside diameter of the
lamp base threads.
The diameter of the base may be specified in
several ways:
- common name (e.g. "candelabra")
- diameter of the base in inch fractions (e.g. 1 1/16")
- the letter "E" and the diameter of the base in millimeters (e.g. E26 is a
base 26mm in diameter)
Here's a table of various screw base sizes:
Bayonet
Automotive turn signal, backup, and marker lights tend to use
bayonet bases because they don't unscrew themselves when vibration is present.
 Notice the small metal nubs sticking out of each side of
the lamp base.
 The bayonet socket has a J-shaped slot on each side, made
to guide the nubs on the base.
The bayonet socket is spring-loaded. You push the lamp down, then twist
slightly to engage the nubs in the hook of the J-shaped slot. When you release
the lamp, spring pressure pushes the lamp nubs up into the hook.
 This automotive lamp has two filaments, for high and low
intensity. The bayonet base has two electrical connections on the bottom. The
nubs on the side are at different heights, so that the lamp will only fit in the
socket one way.
Pins
Some lamps simply have a couple of metal pins sticking out the
back. The MR-n
(e.g. MR-16) type are examples.
T3
I have seen the "T3" designation used for tubular halogen
lamps used in torchier fixtures and "trouble" lights.
The lamps are held by spring-loaded pins that press against the dimples in
the ends of the lamp. The pins also provide electrical contact.
The base designation of "T3" probably refers to the diameter of the lamp. In
order to figure out what size you really need, you also need a length
measurements. Some values are: 78mm, 118mm,145mm, 192mm, 257mm.
Glass Envelope
By "envelope", I mean the bulbous part of the lamp that
contains the filament. And sometimes it isn't really glass.
But either way, the size and shape of the envelope is often used to
distinguish one lamp from another.
An, e.g. A19
The "A" terminology refers to lamps with bulbous
pear-shaped envelopes. The number after the "A" gives the diameter of the widest
part of the lamp envelope in units of 1/8 of an inch. Thus an A19 lamp has a
diameter of 19 times 1/8", or 2 3/8".
PARn, e.g. PAR38
"PAR" stands for Parabolic Aluminized Reflector. This
is a type of sealed-beam lamp with built-in reflector and often a fresnel lens
pressed into the glass. The number after the "PAR" gives the diameter of the
lamp envelope in units of 1/8 of an inch. Thus a PAR38 has a diameter of 4 3/4".
Small PAR lamps tend to use low voltages, and often have a transformer built
into the fixture. Medium-sized PAR lamps use line voltage, and screw bases on
the lamps. Larger PAR lamps tend to line voltage and ceramic connectors that
push on to the lamps.
Some sizes are: PAR36, PAR46, PAR56.
Rn, e.g. R30
The "R" terminology refers to lamps with built-in
reflectors. The number after the "R" gives the diameter of the lamp envelope in
units of 1/8 of an inch.
Here are some Reflector lamp sizes: R20 R30
All of the "R" lamps that I have seen use screw bases.
MR-n, e.g. MR-16
The "MR" terminology refers to miniature reflector
lamps. I think that the number after the "MR" refers to the diameter of the
widest part of the lamp, in millimeters.
I have seen MR-11 and MR-16. Others probably exist.
These tend to be halogen
lamps with bi-pin connections. |
