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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.'" 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 field. 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
phosphors."
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. Webnote 6-1 [SL3 - Section #1 introduction label (2 of 2)] Science after Edison "He was just engaged in fundamental research"
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. Webnote 6-2 [CT2 - vinyl header] [I1L1: interactive intro label] "You can make a lamp that will last forever, but...."
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. Webnote 6-3 [IT1.1 - lamp type #1]
[IT1.2 - lamp type #2]
[IT1.3 - lamp type #3]
[IT1.4 - lamp type #4]
[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. Message:
[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). Message:
Chart F (right wall) shows the relationship between temperature and the range of color produced by a tungsten filament. [I1L2: interactive activity #2] Feeling Light 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. Message:
[I1L6: interactive activity #6] Seeing Infrared 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. Message:
[I1L3: interactive activity #3] Making Color 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. Message:
[L5 - credit label for interactive] Equipment for this display was provided by Maurice Electric Supply Co., and OSRAM SYLVANIA Inc. Graphics:
Graphics from the Illuminating Engineering Society of North America [CL6 - information label]
Incandescent Lamps "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
it was." 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 watt. 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. Webnote 6-4 [L7 - credit label] Objects:
Photo:
[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. Webnote 6-6 [CL8 - information label] Discharge Lamps "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 per watt 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 20,000 hours. Webnote 6-5 [L9 - credit label] Objects:
Photo:
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