20th Century Lamp Preconditions:
Bracketed information [xxx] does not appear on the label.
[ML L1 - Main label LAR2]
LIGHTING A REVOLUTION II
"Before the 1970s the philosophy was 'energy is cheap.'"
Robert Levin, Osram Sylvania scientist, in an interview, 1996
The oil crisis of 1973 marked a turning point. Suddenly energy wasn't cheap at all,
and there was a lot of talk about "efficiency" and "conservation." Lighting engineers
responded like modern-day Edisons, dreaming up new ways to produce light.
In this section of the exhibition, we look at inventors in the late 20th century and
make comparisons with Edison s time a century before. We again consider 1)
preconditions for invention, 2) the inventive process, 3)
promotion of the invention, 4) how success brings competition, and 5)
some of the consequences of an important invention.
We shall also see how concepts of efficiency have come to dominate the lighting
An expanded version of this exhibition can be found on-line. Webnotes on labels
refer to specific places on the website for citations and more detailed information. To
use them, go to the website and click on the Webnotes link. These are also
accessible on the computers in this new section of the exhibition.
The URL for this site is americanhistory.si.edu/lighting.htm
[PT1 - vinyl header]
[SL2 - Section #1 introduction label (1 of 2)]
Technology after Edison
"We wouldn't have CFLs [compact fluorescent lamps] without the rare-earth
Victor Roberts, GE lighting engineer, 1996
Inventors in the late 20th century had access to much technical information that was
unknown in Edison's time. Some knowledge came from outside the industry--like
phosphor work that was done for television. But lighting engineers made many
discoveries, especially in the new industrial laboratories.
In the case to the right, you can see how the incandescent lamp changed during the
early 20th century, principally through the introduction of tungsten filaments. Also shown
are commercially successful gas-discharge lamps.
[references & data on lamps 1900-50]
[SL3 - Section #1 introduction label (2 of 2)]
Science after Edison
"He was just engaged in fundamental research"
William Louden, former GE lighting engineer, 1996
Louden was talking about Joseph Burke, who applied science to what he called the
art of ceramics in experiments with aluminum oxide. It turned out that aluminum oxide
was important for the high-pressure sodium lamp, which you will see later in the
Invention section of this exhibit.
But he could have been talking about a lot of other people. Many scientific
developments applicable to electric lighting appeared during the early decades of the
20th century. Laboratory research into the physics of electrical discharges, the
metallurgy of tungsten, and chemical properties of glass played roles in creation of the
lamps displayed here--all of which were available in the 1930s.
The interactive display Different Ways to Make Light (in the gallery to your right),
allows you to explore some of the science behind electric light.
[references & data on lighting science 1900-50]
[CT2 - vinyl header]
Different Ways To Make Light
[I1L1: interactive intro label]
"You can make a lamp that will last forever, but...."
Victor Roberts, GE lighting engineer, 1996
A filament can continue to glow indefinitely on reduced voltage. Unfortunately, the
light level and efficacy are reduced--a trade-off which is rarely acceptable.
We invite you to use the activities in this display to explore some of the science of
light and color.
[additional data about interactive display]
[IT1.1 - lamp type #1]
Low Pressure Sodium 18 Watts
[IT1.2 - lamp type #2]
High Intensity Mercury Vapor 40 Watts
[IT1.3 - lamp type #3]
Double-coil Tungsten Incandescent 40 Watts
[IT1.4 - lamp type #4]
Fluorescent Tube 15 Watts
[I1L5.1: interactive activity #5 - front of photograph]
Light and Color
Slide this photo beneath each of the lamps and compare its appearance.
What's going on? (see other side)
[I1L5.1: interactive activity #5 - back of photo]
Light and Color
Different lamps emit different combinations of color. The photograph (or any other
object) can reflect only the colors shining on it. This is why it looks different when viewed
under different lamps.
The shaded cover of this exhibit reduces the glare of these bright lamps. It is not
changing the color of the light on the photograph.
Because of color characteristics, a lamp may be ideal for one use and not for
another. For example, low-pressure sodium may be acceptable in street lamps but not
inside most homes.
[I1L1: interactive activity #1]
White Hot Light - Red Hot Light
Turn the knob and watch the spectrum behind the incandescent lamp. Notice that
blue disappears first, then the green as the voltage decreases.
When the filament is very hot it emits the full range of rays that we see as white
light. As you reduce the voltage by turning the knob, the filament s temperature drops.
As the filament cools, it cannot emit the higher energy rays (blue, and then green) and
emits only lower energy rays (red, and invisible infrared which is felt as heat).
The color and energy efficiency of an incandescent lamp depends on the
temperature of the filament.
Chart F (right wall) shows the relationship between temperature and the range of
color produced by a tungsten filament.
[I1L2: interactive activity #2]
Touch the panel in front of each lamp. Can you feel a difference?
The panel in front of the incandescent lamp feels hottest because much of the
energy going into the lamp is radiated as unwanted heat (infrared rays). The other lamps
produce more light and less heat. For instance, the low-pressure sodium lamp emits four
times more visible light and uses only half the energy of the incandescent lamp.
We judge the efficiency of a lamp by the amount of visible light it produces
compared to the energy it consumes.
[I1L6: interactive activity #6]
With the lever up, aim the camera at each light source. Which looks brightest?
Now pull down the lever and look again. Which looks brightest now?
When the lever is up, you see the visible light produced by each lamp in the display.
But lamps also emit rays we cannot see. When the lever is down, the camera acts like
night-vision goggles, allowing you to see the infrared rays coming from each lamp. We
can feel infrared rays as heat but we cannot see them directly, so for lighting a room this
is wasted energy.
Chart E (right wall) shows the sensitivity of the human eye to light rays.
Some lamps are more efficient than others.
[I1L3: interactive activity #3]
Compare the color lines on the graphs mounted under the lamps. Can you find color
lines which appear in more than one? What differences can you see? Compare the
graphs to the color of the lamps.
Atoms and molecules in a lamp emit distinctive colors. The graphs indicate that the
same atoms and molecules may be present in different lamps. The strong blue lines, for
instance, come from the element mercury. Your eye and brain merge these lines to
see an overall color.
Inventors try to choose materials for their lamps to produce desired colors.
[L5 - credit label for interactive]
Equipment for this display was provided by Maurice Electric Supply Co., and
OSRAM SYLVANIA Inc.
- Color spectrum for low pressure sodium lamp
- Color spectrum for mercury lamp
- Color spectrum for tungsten incandescent lamp
- Color spectrum for fluorescent lamp
- Graph showing spectral sensitivity of the human eye
- Graph showing energy distribution of tungsten for different temperatures
Graphics from the Illuminating Engineering Society of North America
[CL6 - information label]
[G-4 - Time line of developments from 1900 to 1950 on counter]
"I remember this circumstance very well because of the excitement and surprise
and incredulity which he manifested at the time. He asked me over and over again what
William D. Coolidge, General Electric scientist, 1909
Coolidge was recounting Fritz Blau s reaction to a lamp made with bendable
(ductile) tungsten wire. Blau, an Austrian, had helped invent a non-ductile tungsten
lamp only a few years earlier and knew well the difficulty of working with this metal.
Coolidge s lamp was not the first improvement in Edison s design, nor was it the
last. It built on previous work (such as Blau s) and fueled new work (such as Irving
Langmuir s). As the technology matured however, the pace of major improvements
slowed. By 1936 almost all of the components of today s light bulb were in place.
[break in label]
1. Tantalum - 1905: [O-3]
Werner von Bolton and Otto Feuerlein, working for Siemens & Halske in
Germany, invented a tantalum filament. It was the first metallic-filament lamp sold in the
United States. Notice how long the filament has to be to give it enough resistance.
Efficacy: 5 lumens per watt.
2. Non-ductile tungsten - 1907: [O-4]
Tungsten seemed like an obvious material for a filament because it has a very high
melting point. But it is also very brittle and hard to form into a wire shape. Even so,
several European inventors developed practical manufacturing techniques. Alexander
Just and Franz Hanaman in Austria, used a chemical process to make a very stiff wire.
Notice how several sections were joined together in series to get a filament with enough
electrical resistance. Efficacy: 8 lumens per watt.
3. Drawn tungsten - 1911:[O-5]
William Coolidge, at GE, developed a ductile tungsten that could be drawn into a
flexible wire. Notice the difference from the previous lamp. Efficacy: 10 lumens per
4. Coiled tungsten; gas-filled; tipless - 1923: [O-7]
Irving Langmuir, at GE, (A) experimented with gas-filled lamps using nitrogen to
reduce evaporation of the tungsten. As a result, he was able to raise the temperature of
the filament. To reduce conduction of heat by the gas, he made the filament smaller by
coiling the tungsten. Notice the mica disc near the bottom, which prevented hot
circulating gas from getting to the base. Notice also the lack of a tip. Early lamps were
evacuated through a tube at the top. Sealing the tube left a pointed tip. By 1920 a
practical way had been devised to evacuate through the base, where the tip could be
hidden. Efficacy: up to 18 lumens per watt.
[filament lamp information]
[L7 - credit label]
- Siemens & Halske tantalum-filament lamp, about 1907 [239,147], from General
- Non-ductile tungsten-filament lamp, about 1908 [1992.0342.16], from the National
Institute of Standards & Technology
- "Mazda B" drawn-tungsten lamp, about 1912 [318,637], from Princeton University
- GE tipless "Mazda C" lamp, about 1925 [1992.0342.23], from the National Institute
of Standards & Technology
- Irving Langmuir with the King of Siam, 1931 [Image #25.046], from the Science
Service Historical Image Collection
[L9.1 - efficacy & lumen label]
Lighting Terms: Lumens, Watts and Efficacy
Lumens: The energy of the visible rays (light) given off per second is
measured in lumens.
Watts: The energy of the electrical input per second is measured in watts.
Efficacy: The energy output divided by energy input is called efficacy and
stated as lumens per watt (lpw). Efficacy is a measure of the efficiency of a lamp in
producing visible light.
[data on efficacy and lumens]
[CL8 - information label]
"We will oppose the use of fluorescent lamps to reduce wattages"
Westinghouse executive, as cited in hearings before the Senate
Committee on Patents, 1942
Westinghouse saw no advantage in promoting a new, more efficient lamp in an era
of falling energy prices. Controlling an estimated 85 percent of the U.S. incandescent
lamp market, GE also had little reason to change. And neither company wanted to
offend electric utilities that purchased power equipment and were not interested in
reducing energy consumption.
Nevertheless, wartime factories began to use fluorescent lamps. And after the war,
with more competition in the lighting industry, their use expanded. By 1951 fluorescent
lamps produced more light than incandescent lamps in the United States.
[break in label]
5. Mercury, low pressure - 1915: [O-10]
Several people worked with mercury discharge tubes in the 19th century. Peter
Cooper Hewitt invented a practical lamp in 1901. In the example here, notice that if the
lamp were tipped properly the liquid mercury would connect the two electrodes. The
electric current through the mercury would heat it until some vaporized. The electricity
would continue to flow as an arc through the vapor, exciting the atoms to give off their
characteristic blue color. This lamp found limited use for industrial applications,
especially photography. Efficacy: 12.5 lumens per watt.
6. Mercury, high intensity - 1933: [O-11]
At higher pressures, the mercury lamp is more efficient. The internal arc-tube (here
Pyrex, but today made of quartz) contains the mercury under pressure. The external
glass tube helps to filter out unwanted ultraviolet radiation. Efficacy: 30 to 40 lumens
7. Sodium, low pressure - 1933: [O-12]
Combined efforts at Philips (Holland), Osram (Germany) and GEC (England)
resulted in a practical low-pressure sodium discharge lamp. The principal challenge was
to develop a glass that would not be corroded by sodium. The characteristic yellow
color limits its applications, but a high efficacy made it and continues to make it popular
for street lighting. Efficacy: originally 40 and now sometimes over 200 lumens per watt.
8. Fluorescent - 1938: [O-14]
In Europe, desire for better efficacy led to early tests of phosphors that could be
stimulated by the radiation in lamps to produce other colors. In the United States, GE,
with help from Westinghouse, introduced practical fluorescent lamps in 1938. Many
were in colors, used for advertising and special displays, but shades of white were also
introduced. Note the electrodes in the ends of this 1934 experimental lamp, the pellet of
mercury, and the hazy phosphor-band around the middle.
Efficacy for white lamps: 30 lumens per watt at the beginning, with a lifetime of 1000
hours. By the end of the century these numbers were 80 to 100 lumens per watt and
[discharge lamp information]
[L9 - credit label]
- Cooper-Hewitt mercury-vapor lamp, about 1920 [1998.0005.10], from OSRAM
- GE high-intensity mercury lamp, about 1934 [318,195], from General Electric Co.
- GE low-pressure sodium lamp, about 1940 [1997.0387.14] from the Mt. Vernon
Museum of Incandescent Lighting
- GE experimental fluorescent tube, about 1934 [1997.0388.41], from General
Electric Lighting Co.
- Worker coating a fluorescent tube with phosphors, about 1940 [Image #25.020],
from the Science Service Historical Image Collection