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The Evolution of Projection Displays. Part I: From Mechanical Scanners to Microdisplays

The development of projection-display systems has encompassed numerous technologies since its beginnings in the early 1930s. CRTs have always played a crucial role, but other critical technologies such as the Eidophor oil-film light valve, Hughes's light amplifier, liquid-crystal devices in various forms, diffraction gratings, mechanical scanners, and digital micromirrors have all played an important role in the evolution of projection systems. The first installment of this two-part article explores the innovations from the 1930s until the early 1990s. In Part II, to be published in the August issue of ID, we'll continue the story to the present day.

by Matthew S. Brennesholtz

THE FIRST electromechanical television system was patented by German scientist Paul Gottlieb Nipkow in 1884, having 18 lines of resolution. It is not known if he built an actual working system. The first recorded working system came in 1902, where synchronized disks rotating at 30,000 rpm were used to produce an image with a 40-Hz frame rate. This would result in a 12.5-line image, except it was not line-scanned; the scan was a spiral. The projected image was so dim it could only be viewed in total darkness. The inventor planned to solve this problem by eliminating the screen and projecting directly on the retina.

While the Nipkow system, as later developed by John Logie Baird, was ultimately unsuccessful in competition against electronic image systems, it established the principle of image transmission by decomposing the image into lines and transmitting the lines sequentially.

 

fig_1_tif

Fig. 1: Layout of Scophony mechanical scanning projection system. Note the use of cylindrical lenses because spherical lenses of sufficient size would have been too expensive.

 

The years 1929–1939 were seminal years for the development of modern television. The question of mechanical vs. electronic TV continued into the 1930s1 and, indeed, continues today. Certainly, electronic scanning at the camera was the clear long-term winner. To modern eyes, it might seem like the electronic answer would be the obvious one for displays as well. On the other hand, disks rotating at the field rate have never really vanished from the television scene. The field-sequential-color system from CBS in the early 1950s used a rotating color wheel, as did color pictures sent from the moon by NASA in the early 1970s. The rotating wheel continues to exist today in most consumer digital light-processing (DLP) systems from Texas Instruments (TI). In addition, scanning mirrors fundamentally similar to the vibrating mirrors described by Priess in 1936 and 1937 are used in modern handheld projector prototypes from companies such as Microvision. Priess could create a picture 3 ft. on a side at a projection distance of 6 ft. In the Priess system, the lamp was modulated, much like the modulation of the laser in a modern laser-scanning system. Priess wrote in 1936: "I do not believe – other things being equal – that the public will choose a small picture system when they have the opportunity of purchasing a large-picture device. They have been trained to theater and home movies."

The Scophony system,2 shown in Fig. 1, was another mechanical projection system developed during the 1930s. Based on two rotating mirrored drums for horizontal and vertical scan, this system featured a light source that operated at a constant brightness and was not directly modulated. Rather, an acousto-optical modulator based on the diffraction of light by sound waves passing through a crystal or fluid was used as a modulator. A dark-field schlieren optical system blocked all undeflected light rays and allowed the diffracted rays to pass on to the scanner and projection screen. The system initially used Kerr cells for the light modulation, but in 1934 switched to the more efficient Jeffree cell. For a 441-line image, the motor driving the high-speed drum needed to rotate at 39,690 rpm. The lifetime of the synchronous motor driving the drum had a nominal lifetime of 1000 hours, although reportedly they actually lasted longer than that. Scophony projection systems intended for public presentations with screens up to 9 x 12 ft. were installed in several theaters. Consumer versions were designed but were never put into production because of the onset of World War II.

Table 1 shows the improvements in television displays from 1929 through 1937.3 In Table 1, the original ratings of candle power per Watt are given, with modern lumen per Watt values in parentheses. The first number is the estimated value if an f/4.5 projection lens (considered a normal lens in 1937) were used while the second value was calculated assuming a modern f/1.0 cathode-ray-tube (CRT) projection lens. While the 5.6 lm/W for a monochrome CRT projector is not competitive with a modern efficiency of about 10 lm/W for a full-color microdisplay projection system, it is still respectable.


Table 1: Improvements in electronic television displays from 1929 through 1937. Modern estimates of lumens per Watt for f/4.5 and f/1.0 projection lenses are given in parentheses.
Year
Lines
Receiver Cost
Color
CandleWatt (lm/W)
Quality
1929
60
$2000
Sepia
1.06
Entirely inadequate
(0.08, 1.7)
1931
120
$2000
Bluish
0.23
Entirely inadequate
(0.02, 0.4)
1934
240
$1200
Greenish
0.86
Hardly passable
(0.07, 1.4)
1936
343
$800
Yellowish-Greenish
1.54
Satisfactory
(0.12, 2.5)
1937
441
$400–$600
White
3.5
Excellent
(0.28, 5.6)

 

fig_2_tif

Fig. 2: Dr. Law with a 3 4-ft. image produced by an RCA projector at the 25th IRE Meeting in 1937. (Photo courtesy of David Sarnoff Library, Princeton, NJ.)

 

The viewing public largely validated these quality ratings, which were based on the best available televisions in a research laboratory, not the ones used routinely in public. For example, the 1936 Berlin Olympics was televised, but was widely ignored by the German public since the poor image quality sometimesmade it impossible to even recognize the images being broadcast. By 1937, these 441-line systems were referred to as "High Fidelity" and even "High Definition" tele-vision.

In 1937, at the 25th annual meeting of the Institute of Radio Engineers (IRE), predecessor to the Institute of Electrical and Electronics Engineers (IEEE), a CRT projector was demonstrated.4 Twelve-hundred IRE members at the Hotel Pennsylvania in New York saw a demonstration of a 10-ft.-diagonal projected image. The monochrome CRT system was built by Dr. Harold Law of RCA Laboratories in Harrison, New Jersey, as shown in Fig. 2. The tube had magnetic deflection, an anode voltage of 10 kV, an image of 1.5 x 2.25 in., a flat faceplate, and a f/4.5 projection lens. The system was normally used to create 3 x 4-ft. images, but for the IRE demonstration it was used to project a 10-ft. image, presumably, with all the room lights off.

The CRT used in this demonstration had a flat faceplate, compared to the convex faceplates of previous projection systems that were needed to provide the glass envelope with suf-ficient strength. The flat faceplate coupled withwhat today seems to be a high-f/# projection lens provided good focus across the full screen. For previous convex faceplates, it had been necessary to compromise center-to-edge focus quality.

By 1937, surprisingly modern CRT projectors were appearing in the literature. For example, M. Wolf5 published a paper on a rear-projection system that would be recognizable as a modern CRT projector except it was monochrome. The system used a concave faceplate instead of a convex or flat one. According to Wolf, to obtain satisfactory focus quality on a flat faceplate, the central area no larger than 48-mm diameter could be used. With the concave faceplate designed to match the curvature of the image plane of the f/1.9 projection lens used, Wolf could focus the 48 x 55-mm 405-line image from the CRT faceplate onto a rear-projection screen that could be as large as 100 x 120 cm, although a 40 x 50-cm screen was used more commonly. The tube used 20–25-kV anode voltage and magnetic focus and deflection. With the anode at 25 kV and the grid at 0 V, 400–800 μA could be produced with a spot size of 0.1 mm. The system produced 4–8 lux.6 This was considered inadequate by Wolf and Philips, so they used a screen with an estimated gain of 2.5 and provided an estimated viewing angle of ±25°.

 

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Fig. 3: First prototype of the Eidophor large-screen projection system as demonstrated in 1943.

 

Oil-Film Light-Valve Projectors

During World War II, most television and CRT research was directed toward military purposes such as radar and remote guidance of weapons. However, research into television projection systems continued during that time in Switzerland, a neutral country. Professor Fritz Fischer, working at the Technical Physics Department of the Swiss Federal Institute of Technology in Zurich, built the first prototype of what would later grow into the Eidophor7 projector from 1940 through 1943. This prototype, shown in Fig. 3, was demonstrated on New Year's Eve in 1943.

Here is how the eidophor worked. An electron beam wrote a diffraction grating onto the surface of a thin layer of oil in a vacuum. The optical path of both systems was dark-field schlieren, as shown in Fig. 4. When the surface was flat there was no diffraction, the light passing through the oil film hit the schlieren stop and that portion of the image produced a dark area on the screen. When the electron beam, which ran at a constant current, was wobulated with an RF field, the charge distribution on the oil film was non-uniform and the surface deformed under the electrostatic forces. These surface deformations diffracted the light so it missed the Schlieren stop and was projected onto the screen. A Schlieren lens ensured all diffracted light missed the stop and all undiffracted light hit the stop. The projection lens worked with the schlieren lens to image the oil film on the projection screen. Note that the light was diffracted, not refracted or scattered. Regardless of the amplitude of the diffraction grating on the oil film, the diffraction angle was always the same. Low-amplitude diffraction gratings left most of the light in the zeroth order, producing a dark but not black spot. High amplitude produced maximum white.

While, obviously, there was nothing "Micro" about this system, it had all the aspects of a modern microdisplay projection system, including an external light source, a small image to modulate the light, and a projection lens to generate the image on the screen. The Scophony system and other mechanical scanning systems scanned the light and generated the image by modulating the light intensity. In the Eidophor and other light-valve, light-amplifier, and microdisplay systems, the light is not scanned. Instead, the light is steady, illuminates the entire image simultaneously, and the scanning is done electronically in the microdisplay.

The 1943 system used a carbon arc source, the brightest and most compact source at the time (Fig. 4). In 1957, when the first pre-production Eidophor system was under construction, it was switched from a carbon arc lamp to a 1600-W high-pressure xenon lamp introduced by Osram.

In 1953, a color field-sequential Eidophor was demonstrated at the Pilgrim Theater in New York City. 20th Century Fox was impressed and ordered two improved models. The contract for these projectors required the electronics be built by General Electric (GE), so they were shipped to Syracuse, New York, for this work in 1955.

A planned follow-on order for 1000 of these color sequential units was put on hold and ultimately canceled with the introduction of the RCA simultaneous color transmission system. Another factor in the cancellation was the development of Cinerama and Cinemascope, which drew viewers back into the theaters and reduced the perceived need for theater television systems. A final issue would be familiar to modern ears: the theater owners and studios could not agree on how the projectors would be paid for and what type of television content could be shown.

 

fig_4_tif

Fig. 4: Principle of operation of an oil-film, dark-field, schlieren optical system.

 

The prototype simultaneous color Eidophor system had four channels: red, green, blue, and white. Tests of this monster machine where all four channels were in a single vacuum chamber were disappointing: the system could only be used to make a 3 x 4-m image on a 196-in.-diagonal screen. While the system had been paid for by 20th Century Fox, it was never shipped to the U.S. and went into storage.

In 1958, Gretag decided to go into production with the Eidophor. Six pre-production Model ep.1 units were built; four were finished as color-sequential projectors with 500 lm and two as black and white systems with about 2000 lm. This was followed by full production of Model ep.2 with a planned production rate of 5 units/ per month. Gretag did not have the marketing or support networks needed for full production. Therefore, CIBA, Gretag's parent company at the time, set up a joint venture with Philips called Eidophor, Ltd., to market and support the projectors. The first production unit was sold as a color-sequential version to Redifon, Ltd., in England for use in a flight simulator.

Gretag returned to the multi-channel design in 1961, using a more-conventional three-channel system. Gretag designed the basic projector while Philips developed the electronics. This projector is shown in Fig. 5 and produced 2500 lm from the 1600-W xenon lamp, the brightest color-television image that had been shown to date. Note the prominence of the protective cover over the electron gun. Access to the electron gun was needed because the lifetime of a cathode in the Eidophor was at best 100 hours. The cathode could be replaced in approximately 2 minutes by the operator, minimizing disruption of the performance, since the other two color channels continued to operate. With a three-channel Eidophor used 12 hours a day, this failure and cathode change during a performance could occur several times a week.8

Gretag continued to bring out new models with improved light output and reduced service requirements. Eventually, they reached 4000 lm from a 2500-W xenon lamp. In 1965, Gretag signed an agreement with JVC to produce Eidophor projectors in Japan. The first projector built in Japan was finished in 1967. Unfortunately, JVC had tooled up to produce the single-channel version, which could be used either as a black-and-white projector or as a color-sequential one.

Demand for these types was dwindling while demand for the simultaneous three-color projectors was increasing. Changes in the oil material used that simplified the design of the projector and made the system more reliable also reduced the response speed of the oil film, so the Eidophor could no longer operate in a color-sequential mode. JVC ceased production after building nine Eidophors.

New models of Eidophor projectors continued to be developed and sold into a variety of professional markets. By 1989, there were about 600 projectors in use worldwide. With the introduction of first LCD and later DLP projectors with comparable brightness and image quality, demand for the Eidophor declined rapidly. The Gretag Display Systems Division closed at the end of 1997, after pro-duction of approximately 650 projectors. AmPro of Melbourne, Florida, acquired Gretag's Eidophor business in 1998. They are believed to have built a few projectors from existing parts acquired from Gretag. Support for all Gretag Eidophor projectors came to an end in June 2000. The last Eidophor was believed to have been removed from service in 2000.9

Talaria Projectors

The Talaria projector was developed under the technical leadership of Bill Glenn at GE in Syracuse, New York, and the first systems appeared in 1958.10 The initial Talaria system was introduced in monochrome and color versions. A 1977 Talaria model is shown in Fig. 6. The Talaria projector was similar to the Eidophor in some ways, and derived some of its technology from the Eidophor during the 1955–1958 time period when Gretag and GE were cooperating. But the Talaria was not just a copy of the Eidophor; it had several major differences, including:

• The light valve was transmissive rather than reflective.

• The light valve was sealed and no vacuum pump was designed into the projector.

• The initial color design used a single light valve to produce all three colors without color-sequential operation.

 

fig_5_tif

Fig. 5: Eidophor Model ep.6 simultaneous color projector capable of 2500 lum.

 

Each of these changes conferred a major cost advantage on the Talaria compared to the Eidophor. The transmissive optical path was simpler and more compact than the Eidophor's reflective path. The sealed light valve, designated the T1, not only eliminated the vacuum pump, reducing cost and making the system more compact, but it increased the lifetime of the system to several thousand hours. It also reduced the warm-up time from the 1 hour reported for the Eidophor to about 30 minutes, since no time was used to pump the system down to a vacuum on start-up. The remaining warm-up time was needed to bring the oil up to its operating temperature.

Since the initial color Talaria was a full-color single-light-valve design, no optical convergence was necessary. On the other hand, the Talaria had about 46 trim pots that needed to be set up correctly in order to get a proper image on the screen, a formidable task for even the most experienced engineer at GE. The single-light-valve design of the Talaria limited it to about 600–1000 lm, depending on the model and the lamp power. There were also serious color and gamma artifacts in the image. The physics of the Talaria was similar to the physics of an Eidophor.

The full-color Talaria operated by wobulating the electron beam with three different radio frequencies, producing diffraction gratings with three different spatial frequencies on the oil film. The color-segmented pupil and the Schlieren bars were designed to have each RF modulate only one wavelength band of light (red, green, or blue). This minimized but did not fully eliminate interactions between colors. Red and blue, in particular, interacted strongly, especially in the mid-brightness levels.

Operation of the transmissive Talaria system shown in Fig. 6 was very similar to the operation of the reflective Eidophor. The effect of the diffraction gratings was doubled because of the double pass, requiring lower modulation of the oil film to achieve maximum white.

To overcome the brightness and color problems, a version of the Talaria with two light valves called the MLV was introduced in 1987.11 This unit had one monochrome light valve dedicated to green and one two-color valve split between blue and red. Each light valve had its own xenon lamp. The two images were then converged at the screen. This dramatically improved the colorimetry of the system because a Talaria light valve could satisfactorily modulate two colors with diffraction gratings parallel and perpendicular to the raster lines. The third color, however, was modulated by a second diffraction grating with a different spatial frequency also perpendicular to the scan lines. These two parallel gratings, used to modulate red and blue light in the single-light-valve version, interacted with each other to affect the color. In the MLV, the red/blue light valve used diffraction gratings perpendicular to each other to modulate the light, avoiding this problem.

The ultimate Talaria contained three monochrome light valves and three lamps. Again, all light valves were screen-converged to produce the full-color image. The 3LV (Fig.7) could produce about 7000 lm at the screen, if a handy 50-A 230-V outlet was available.

Cost was a serious problem with the Talaria projectors, as can be seen in the 1992 MSRP price list shown in Table 2. The light outputs in Table 2 are approximate for two reasons. First, output of Talaria varied from projector to projector. Second, 1992 was before ANSI lumens were commonly used, so the specified lumens for these projectors was not measured by a standard method. For example, the 10k in LV 10k stood for 10,000 "CRT equiva lent peak lumens." This measure was typically 3x–10x what would be measured by the ANSI lumen test method.

 

fig_6_tif

Fig. 6: 1977 Talaria PJ5050 Projector, mounted on optional accessory stand. Detachable control unit allows remote operation to 200 ft.

 

fig_7_tif

Fig. 7: 1991 Talaria 7000 Lumen 3LV Projector.

 


Table 2: Price list for Talaria single-light-valve LV series and two-light-valve MLV projectors in 1992.
Model
List Price
Appoximate lm
LV7000 DF
$46,980
700–1000
LV7000 MP
$56,950
700–1000
LV10k DF
$79,980
1000–1300
LV10k MP
$89,950
1000–1300
MLV-SC
$149,750
2500–3000

 

The T1 light valve remained in production in monochrome, two-color, and three-color versions, essentially unchanged from the first experimental units in 1958 until the business was shut down in 1994. General Electric sold its Talaria business along with its defense business to Martin Marietta in 1993.12 which in turn sold the Talaria business to NEC in 1994. Like the Eidophor, the Talaria was unable to handle the competition from LCD projection systems such as the Barco Light Cannon and went out of production shortly after the sale to NEC. While no Eidophor projectors are believed to be operable today, functioning Talaria with its sealed light valve still remain in service. Due to the very high operating cost for a Talaria (estimated in 1992 to be about $100 per hour), plus the difficulty in getting service and replacement parts,13 it is believed that the Talaria remaining in service today are targeted for replacement. For example, in 2006, the Dutch National Aerospace Laboratory replaced the Talarias in its F-16 pilot-training simulator with Barco SIM6 Ultra II projectors.14 The Barco press release said its projector represented "an ideal replacement for the end-of-life Talaria projectors because they fit perfectly with the complex existing configuration."

CRT Projectors in the Post-War Years

Research and development into CRT projection systems continued through World War II. In the post-war years, a number of CRT projectors were installed in theaters. In 1948, RCA demonstrated a balcony-mounted projector that used a 15-in. CRT with an anode voltage of 80 kV, as shown in Fig. 8. The Schmidt-type optical system consisted of a 500-lb. 42-in. mirror with a 36-in. lens.

By 1951, there were about 100 theater projector installations, with RCA having about a 75% market share. That year, there were about 300 live shows transmitted. For example, in 1952 the Opera "Carmen" was cinema-cast in black-and-white live from the Metropolitan Opera in New York to movie theaters in 27 cities.

Color CRT projection systems have almost always used three CRTs. Figure 9 shows a 1951 color CRT theater projector specifically designed to receive the simultaneous color video signal proposed by RCA that was eventually adopted as the NTSC color standard.15

The consumer was not ignored by the CRT projection business. CRT projectors were sold, or at least offered for sale, to consumers interested in images larger than the direct-view televisions of the time could produce. Figure 1016 shows a 1951 advertisement for a TV projector for £146.15. At an exchange rate of $5/£, this is a total of $734.

In the 1950s and 1960s, the interest in CRT projection systems declined for large-screen applications because they could not compete with light-valve projectors such as the Eidophor and Talaria. The consumer-electronics industry produced direct-view CRTs in larger and larger sizes, reducing the need for projection systems. During this period, the CRT projector was mostly limited to professional applications where the screens were not large enough to justify the use of a light-valve projector.

The lull in consumer CRT projectors ended in 1972 with the introduction of the Advent VideoBeam projector with Schmidt optics, developed by Henry Kloss from a design by Art Tucker.17 In the Tucker and Kloss designs, the Schmidt mirror was inside the CRT vacuum-tube envelope. While this ensured the mirror remained clean, it lead to a very expensive CRT. This cost was acceptable in a military simulator where the alternative at the time would have been an oil-film light valve, but a difficult sell in the consumer market.

The VideoBeam was a two-piece three-CRT system housed in a coffee-table-sized console with the picture projected on a 7-ft.-diagonal curved aluminized screen that had to be placed precisely 8 ft. away. Kloss left Advent in 1976 and founded Kloss Video, where he built the NovaBeam series of CRT projectors of similar design to the VideoBeam. Again, the high prices of the Advent and Kloss Video systems prevented widespread sales, and Advent went bankrupt in 1981. Kloss Video was eventually bought by Ampro.

While at the time, Kloss got much of the publicity, other companies introduced CRT front projectors of a more conventional design. In 1972, for example, Sony also introduced its popular VPH series of CRT projectors intended primarily for professional applications. These continue to be popular with home-theater enthusiasts to this day.

Consumer-electronics manufacturers concentrated on CRT projection systems in the years following the re-introduction of consumer projection by Kloss, Sony, and others. Products included two-piece front-projection systems such as the Advent 760; one-piece front-projectors such as the Advent VB125, Sony KP-5000 and Quasar PR6800QW; and one-piece rear-projection systems such as Quasar CT-4500 "CinemaVision" with a 45-in. screen. The sales of large-screen consumer systems was spurred, in part, by the introduction of Beta and VHS videotape systems in 1976. While the Sony Beta system initially only had a 1-hour capacity, the JVC VHS system introduced only months after Beta had up to 2 hours of capacity. This made most films available in prerecorded form, and consumers wanted to watch these films on large screens.

 

fig_8_tif

Fig. 8: 1948 RCA Monochrome CRT Projector for Theatrical Use with a 15" CRT and 42" Schmidt Optics (Photo courtesy of Radio Age)

 

Two key product introductions in 1979 enabled the rapid growth of the rear-projection TV business. The first was the f/1.0 projection lens from U.S. Precision Lens. This extremely low f/# allowed the collection of enough light to make an image of sufficient brightness. While a f/1.0 refractive lens did not collect as much light as af/0.7 mirror in the Schmidt optical system used by Advent and Kloss video, it cost much less and produced enough light when a relatively high-gain rear-projection screen was used. By the 1980s, these lenses were typically liquid coupled in a process originally developed for military CRTs. This increased the brightness at the screen by cooling the tube, allowing higher powers. The elimination of the air space also eliminated reflections and increased brightness and contrast.

A liquid-coupled CRT projection lens is shown in Fig. 11.18 While this particular design comes from USPL near the end of the CRT projection business, it has design features common with all liquid-coupled lenses. The liquid was contained between the CRT faceplate and a deeply curved thin element. This lens element/liquid combination formed a strong negative lens near the image plane. The effect of this lens was to correct the field curvature of the lens/faceplate combination so the image could be focused on the flat projection screen, a problem discussed by Wolf in 1937. This design has five elements but other designs had either four or six elements, depending on the vintage and the quality of the image to be produced. Typically, one of the elements would have most of the power in the lens, L2 in Fig. 11, while the other elements served to correct aberrations introduced by this strong wide-field-of-view low-f/# element.

The second enabling product was the development of the color-corrected lenticular projection screen commercialized by Freen Screen. Rear-projection screens based on Fresnel lenses had been around since 1940.19 These screens were intended to have the image source on axis and were not suitable for use in high-gain three-CRT rear-projection designs. This problem was solved with the invention of a color-correcting screen in 1970.20 This color-correcting screen allowed the use of off-axis CRTs in relatively high-gain screen applications. With previous high-gain screen designs, the on- and off-axis CRTs produced angular light distributions that differed from each other, leading to color shifts for viewers that were not on the centerline of the screen.

While growth in consumer CRT rear-projection systems continued through the 1980s and 1990s, professional CRT projectors felt the same pressure from LCD, DLP, and LCoS systems that had doomed the Talaria and Eidophor, especially at lower resolutions. For example, in the 1998 projection shoot-out at Infocomm,21 there were only six CRT projectors in the VGA, SVGA, and XGA categories. In the high-resolution 1280 x 1024/1600 x 1200 section, there were four CRT projectors, and only a single LCD projector, from ASK.

Hughes/JVC ILA projectors

The Hughes Light Amplifier LCD technology began at the Hughes Aircraft Research Labs (HRL) in Malibu, California, in the 1970s. Solid-state physicist W. P. Bleha and liquid-crystal scientists J. D. Margerum and A. M. Lackner developed a photoconductor/liquid-crystal image spatial light modulator. While the original intention had been to develop an optical signal-processing system for use with lasers, another HRL development, the value of the system as a display was recognized. In a display application, the photoconductor was driven by an image generated on a CRT and relayed to the photoconductor surface. The spatial variation of the conductivity of the photoconductor changed the spatial voltage distribution on the liquid crystal. This in turn spatially changed the liquid-crystal orientation and controlled the polarization of the light from an external lamp. This use of a dim CRT image to control a very bright image at the screen led to the phrase "Light Amplifier," although at the time the technology was more commonly known as a liquid-crystal light valve (LCLV). By 1972,22 this system had shown sufficient image quality to interest the U.S. Navy in the use of the system for a shipboard display. A full-color version of the projector suitable for television was developed by 1977.23 Production of the LCLV began for the U.S. Navy and Air Force began in the early 1980s.

 

fig_9_tif

Fig. 9: RCA Tri-color receiver-projector, which provides theater-size screen images, is shown with its developer, Dr. David Epstein (Photo courtesy of David Sarnoff Library, Princeton, NJ)

 

In the 1980s, Hughes continued to develop the technology and developed the second-generation LCLV, based on an amorphous-silicon photoconductor. The higher speed of silicon allowed full-motion high-resolution video images to be displayed. In addition, the homeotropic alignment of the liquid crystal was stabilized leading to substantially improved contrast ratio over the hybrid field-effect mode that had been used in the first-generation Hughes LCLV.

Interest in LCLVs was not limited to Hughes. For example, the November 15, 1989 special issue of Applied Optics had 26 papers on spatial light modulators, most of them based on liquid crystals. The 89 authors of these papers included representatives of 30 different institutions, including of course, Hughes and Texas Instruments. Several of the institutions were represented by several papers. One of the papers,24 while not intended as a review paper, had a massive bibliography of 89 references.

Hughes Aircraft Co., recognizing the future commercial importance of this display, spun off the LCLV activities into a subsidiary, Light Valve Products, Inc., in 1989. At this time, the LCLV was given the trademarked name ILA or Image Light Amplifier. Soon Light Valve Products, Inc., was demonstrating large-screen displays for digital cinema in Hollywood and large-venue applications.

In 1992, Hughes and JVC formed a joint venture, the Hughes-JVC Technology Corp. (HJT), to produce ILA projectors and take advantage of the global JVC operations. From 1992 to 2000, HJT shipped over 3500 ILA projectors into large-venue applications around the world. In June 1999,25 two 12,000-lm ILA projectors from HJT were used for the world's first demonstration of digital cinema to paying customers when Star Wars Episode 1 was shown in Los Angeles and New York. The projectors used were similar to the one shown in Fig. 12. Simultaneously, DLP projectors from Texas Instruments showed the same movie in two other theaters, also in Los Angeles and New York.

 

fig_10_tif

Fig. 10: British advertisement for a CRT projection system in 1951 from the Daily Mail "Guide to Television."

 

HJT worked with JVC to develop the D-ILA microdisplay, which was launched in 1997. In this system, the LC drive voltage produced by the a-Si photoconductor was replaced by a voltage drive from an active-matrix silicon backplane. This eliminated the bulky, troublesome, and expensive CRT used to generate the image. This significantly reduced the size of the panels and the optical system. Although single-lens ILA projectors had been built,26 their performance was not fully satisfactory compared to the three-lens versions. The smaller size of the D-ILA panel not only allowed single-lens operation but it enabled the development of consumer versions of the D-ILA system. Improvements in optical components and architectures were also instrumental in the development of single-lens LCoS projectors.

In the next installment of this article, in the August issue of Information Display, we will continue the chronology and explore how the development of LCOS, DLP, and LCD technologies threatened the dominance of light valves and CRTs as the industry of projection displays took on the period from the 1990s to the 2000s.

References

1W. H. Priess, "Mechanical vs. cathode television systems," Radio-Craft, 79 (August 1936).

2F. Okolicsanyi, "The wave-slot, an optical television system," Wireless Engineering 14, 526 (1937).

3W. E. Shrage, "The balance sheet of televi-sion," Radio-Craft 9, No. 2, 80 (August 1937).

4"The projection kinescope makes its debut," Radio-Craft 83 (August 1937).

5M. Wolf, "The enlarged projection of television pictures," Philips Technical Review 2, No. 8, 249–253 (August 1937). Gain and viewing angle were estimated by MSB by scaling from the drawings in the paper.

6Lux is a measure of illuminance and is not used in modern reports of projector output. Presumably, Wolf measured the illuminance provided by the CRT projection system at theimage plane with the projection screen removed.

7H. Johannes, The History of the EIDOPHOR Large Screen Television Projector (Gretag Aktiengesellschaft, 1989), p. 110.

8Interview with Phillipe Roth, optical specialist in the R&D Lab Systems Division of Gretag Imaging, as reported in http://www. spgv.com/columns/eidophor.html.

9 http://www.cinephoto.co.uk/eidophor.htm.

10W. E. Glenn, "New color projection system," J. Opt. Soc. Am. 48, 841–843 (1958).

1 T. T. True, "High-performance video projector using two oil-film light valves," SID Symposium Digest Tech Papers 18, 68–71 (1987).

12General Electric 1993 Annual Report.

13Replacement Talaria parts including light valves are still available from Vacuum Optics, http://www.vacuumoptics.com/.

14Barco Press release, "Barco brings fresh light and vision to Dutch National Aerospace Laboratory NLR" (11 December 2006); http://www.barco.com/corporate/en/press releases/show.asp?index=1860.

15The Story of Television (Radio Corporation of America, 1951).

16F. Coven, ed., Television Guide (Daily Mail, London, 1953), p. 128.

17W. E. Good, "Projection television," Proc SID 17, No. 1, 3–7 (1976).

18J. Moskovich, "High performance projection television lens systems," U.S. Patent 6,509,937, Issued January 21, 2003 and assigned to U.S. Precision Lens.

19J. D. Strong and R. Hayward, "Transparent projection screen," U.S. Patent 2,200,646, Issued May 14, 1940.

20W. E. Glenn, Jr. (Assigned to GE), "Composite back projection screen," U.S. 3,523,717, Issued August 11, 1970.

21P. H. Putman, Infocomm '98: A Review (1998); http://www.digitalcontentproducer. com/mag/avinstall_infocoreview_2/index. html.

22 A. D. Jacobson, W. P. Bleha, Jr., D. D. Boswell, M. Braunstein, J. D. Margerum, and S-Y. Wong, "Photo-activated liquid crystal light valve," SID Symposium Digest Tech Papers 3, 70 (1972).

 

fig_11_tif

Fig. 11: High-Performance, Liquid Coupled CRT Projection Lens from U. S. Precision Lens

 

23A. D. Jacobson, D. O. Boswell, J. Grinberg, W. P. Bleha, P. G. Reif, B. Hong, S. Lunquist, and J. Colles, "A new color TV projector," SID Symposium Digest Tech Papers 3, 106 (1977).

24K. M. Johnson and G. Moddel, "Motivations for using ferroelectric liquid crystal spatial light modulators in neurocomputing," Appl. Opt. 28, No. 22, 4888–4899 (1989).

25R. D. Sterling and W. P. Bleha, "D-ILA technology for electronic cinema," SID Symposium Digest Tech Papers 31, 310 (2000).

26A. G. Ledebuhr, "Full-color single-projection-lens liquid-crystal light valve projector," SID Symposium Digest Tech Papers 17, 379–382 (1986). •

 

fig_12_tif

Fig. 12: Hughes/JVC 12K projector used in 1999 digital-cinema tests.

 


Matthew Brennesholtz is Senior Analyst at Insight Media, 3 Morgan Ave., Norwalk, CT 06851; telephone 203/832-8464, e-mail: matthew@insightmedia.info.