United States Patent [191
`Baur et a1.
`
`[11]
`[45]
`
`4,142,781
`Mar. 6, 1979
`
`[73] Assignee:
`
`[54] ELECT RO-OPTICAL DISPLAY DEVICE
`WITH ELECTRO-OPTICAL LIGHT VALVES
`[75] Inventors: Guenter Baur, Freiburg; Waldemar
`Greubel, Denzlingen, both of Fed.
`Rep. of Germany
`Siemens Aktiengesellschaft, Berlin &
`Munich, Fed. Rep. of Germany
`[21] Appl. No.: 747,035
`[22] Filed:
`Dec. 2, 1976
`[30]
`Foreign Application Priority Data
`Dec. 3, 1975 [DE] Fed. Rep. of Germany ..... .. 2554226
`Apr. 15, 1976 [DE] Fed. Rep. of Germany
`2616669
`Sep. 10, 1976 [DE] Fed. Rep. of Germany
`2640909
`
`[s1] 1m.c1.2 .............................................. .. cozr 1/13 ,
`[52] US. Cl. ................................ .. 350/345; 350/ 338
`[58] Field of Search .......... .. 350/ 160 LC, 150, 160 R,
`350/338, 345, 357
`
`[56]
`
`3,837,729
`3,838,908
`
`References Cited
`U.S. PATENT DOCUMENTS
`9/ 1974
`Harsch ........................ .. 350/ 160 LC
`10/1974 Charmin ...................... .. 350/160 LC
`
`3,840,695 10/1974 Fischer ................... .. 350/ 160 LC X
`3,864,905
`2/1975 Richardson ..
`0/160 LC X
`3,869,195
`3/1975_ Aldrich et al.
`350/ 160 LC
`3,950,078
`4/ 1976 Zatsky ................. .. 350/160 LC
`3,994,564 11/1976 Somogyi ................. .. 350/160 LC
`3,994,565 11/ 1976 van Doom et a1. ........ .. 350/ 160 LC
`4,042,294
`8/1977 Billings et al. .............. .. 350/ 160 LC
`4,043,636
`8/1977 Eberhardt et a1. .......... .. 350/ 160 LC
`
`Primary Examiner-Edward S. Bauer
`Attorney, Agent, or Firm--Hill, Gross, Simpson, Van
`Santen, Steadman, Chiara & Simpson
`[57]
`ABSTRACT
`Electro-optical display device which may operate ei
`ther in a one or multi-color mode and utilizes electro
`optical light valves for controlling transmittance of a
`passive light through the device characterized by pas
`sively amplifying the brightness of the display device
`with the addition of a light trap which includes a ?uo
`rescent plate having mirrored edge surfaces. While the
`invention or improvement may be utilized with any
`passive optical display device, it is particularly useful
`with a liquid crystal display device.
`
`36 Claims,‘ 20 Drawing Figures
`
`Sony Corp. Exhibit 1008
`
`SONY_000660
`
`

`
`Sheet 1 of 9
`
`4,142,781
`
`SONY_000661
`
`

`
`US. Patent Mar. 6, 1979
`
`Sheet 2 of9
`
`4,142,781
`
`'IL
`
`12’
`
`/
`
`SONY_000662
`
`

`
`.8. Patent Mar. 6, 1979
`
`Sheet 3 of9
`
`4,142,781
`
`Fig. 5
`
`Fig.6
`
`00
`
`O
`O
`O
`
`O
`
`2
`,3 J/
`l
`‘1
`l
`/
`a
`
`2
`
`/3
`[1,9
`/
`1
`/
`g
`‘5/ /
`2\,|
`y’
`I
`h‘
`I
`iv'v
`
`17/1- J31? - - - - -—?—
`
`SONY_000663
`
`

`
`US. Patent Mar. 6, 1979
`
`Sheet 4 of 9
`
`SONY_000664
`
`

`
`US. Patent Mar. 6, 1979
`
`Sheet 5 of9
`
`SONY_000665
`
`

`
`US. Patent Mar. 6, 1979
`
`Sheet 6 of9
`
`4,142,781
`
`Fig. 10
`
`2B
`
`27
`
`Fig 11
`
`Fig. 12
`
`90°01,
`
`SONY_000666
`
`

`
`U. Patent Mar. 6, 1979
`
`Sheet 7 of9
`
`4,142,781
`
`SONY_000667
`
`

`
`US. Patent 'Mar.6, 1979
`
`Sheet 8 of9
`
`4,142,781
`
`Fig.14
`
`2a 120
`
`100 -
`
`8U -
`
`SONY_000668
`
`

`
`atent Mar. 6, 1979
`US, "
`
`Sheet 9 of 9
`
`4,142,71
`
`dun
`
`50D
`
`6110mmI 7m
`
`'sbu‘ '
`
`' '7'uu' l>\l(nlmil
`
`SONY_000669
`
`

`
`1
`
`5
`
`4,142,781
`2
`or shutter for controlling the transmittance of passive
`light through the display plate with the improvement
`causing a more effective exploitation of the ambient
`light.
`To accomplish these goals, an optical display device
`having a display plate with at least one electro-optical
`light valve for controlling transmission of the passive
`light through the display plate has the improvement
`comprising means for entrapping light and passively
`amplifying the brightness of the display device, said
`means including a ?uorescent plate having mirrored
`edge surfaces so that the light is entrapped in the ?uo
`rescent plate and directed through each of the light
`valves.
`The passive brightness ampli?cation is primarily
`suited for all liquid crystal effects in which it is possible
`to switch between a light blocking and a light transmis
`sive state by an electrical ?eld being applied on a liquid
`crystal layer. This light valve effect can be achieved in
`all liquid crystal effects used in displays with the aid of
`known additional polarizers and possibly further pas
`sive optical elements. Special advantages occur with the
`combination of the ?uorescent plate in a display having
`a so-called rotational cell with polarizers extending
`parallel to each other.
`The present invention essentially exploits a phenome
`non which is using a thin synthetic material plate in
`which ?uorescent materials are dissolved to trap or
`collect ambient light. The trapped light is conveyed
`with a high degree of effectiveness to reexit in a visible
`and meterable manner at arbitrary points on the plate.
`When a ?uorescent plate of this type is combined with
`various types of passive electro-optical displays, which
`functions as light valves, an increased ambient bright
`ness adaptive illuminous density of the display elements
`which are electrically regulated or controlled between
`a light transmissive state and a light scattering or block
`ing state is produced.
`
`25
`
`ELECTRO-OPTICAL DISPLAY DEVICE WITH
`ELECI‘RO-OPTICAL LIGHT VALVES
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention is directed to electro-optical
`display devices which include single and multi-color
`display devices which utilize electro-optical light
`valves such as a liquid crystal cell for controlling trans
`mittance of a passive light from the display device.
`2. Prior Art
`Many different types of passive display devices are
`known. Examples of known passive display devices
`include electrophoretic, electrochromic, liquid crystals
`and ferroelectric displays.
`.
`Liquid crystal displays can be based on dynamic scat
`tering as discussed in an article by G. H. Heilmeier, L.
`A. Zanoni, and L. A. Barton, Proceedings of the IEEE,
`Vol. 56, No. 7, July, 1968, pp. .1162. In addition, liquid
`crystal displays may be used as rotational cell as dis
`cussed in German Offenlegungsschrift Nos. 21 58 563
`and 22 02 555.
`'Ferroelectric displays may use linear or quadratic
`electro-optical refraction effects in a ferroelectric ce
`ramic as discussed in articles by G. H. Haertling and C.
`E. Land, Journal of American Ceramic Society, Vol. 54,
`1971, page 1 and by J. R. Maldonado and A. H. Meit
`'zler, Proceedings of IEEE, Vol. 59, 1971, page 368. In
`addition, ferroelectric displays may utilize electro-optic
`scattering effect in the ferroelectric ceramics as dis
`cussed in an article by W. D. Smith and C. E. Land,
`Applied‘ Physics Letter, Vol. 20, 1972, page 169.
`Electrochromic displays may utilize an electrochro
`mic effect, for example, in a solid state ?lm of W03 or
`M003 with a redox reaction'in the boundary layer with
`electrolytes such as H2504 as discussed in the article by
`S. K. Deb, Appl. Opt. SuppL, Vol. 3, 1969, page 192.
`Each of these types of display devices possesses es
`sentially three fundamental advantages. These advan
`tages are a small consumption of electrical energy, a
`contrast which is largely independent of the ambient
`brightness, and a ?at type of construction. However,
`there are some disadvantages. When the display is oper
`ated in a transmission mode with a light source located
`behind the display, the advantage of a ?at type of con
`struction is lost.
`In a re?ecting mode of operation, the ambient light
`which enters from the viewers side is turned back or
`re?ected back by a re?ecting layer in the direction
`toward the viewer through the display where it is spa
`tially modulated. In the known display devices, this
`type of operation has the disadvantage which is that a
`relatively good readability of the display is only possi
`ble under restricted viewing conditions. For example,
`the incident light may cause a shadow of the display
`element to be cast upon the re?ecting surface which
`shadow may interfere with the display. In addition to
`the above problems, many of these displays, such as
`liquid crystal displays which rely on a field effect basis
`require polarizers, and the polarizers will weaken the
`representational contrast which will further reduce the
`viewing conditions.
`a
`.
`SUMMARY OF THE INVENTION
`The present invention is directed to an improvement
`in the readability of an optical display device having
`display plate with at least one electro-optical light valve
`
`40
`
`45
`
`50
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an exploded presentation of an electro-opti
`cal display device with passive brightness ampli?cation
`using a light trap comprising -a ?uorescent plate posi
`tioned behind the electrically controllable light valves
`in accordance with the present invention;
`FIG. 2 is a cross-sectional view of an electro-optical
`device using a light trap having a ?uorescent plate dis
`posed in front of the light valves and a second plate
`disposed behind the light valves;
`FIG. 3 is a cross-sectional view of an electro-optical
`display device with a light trap for the passive light
`ampli?cation in which the trap comprises a ?uorescent
`plate in front of the electro-optical controllable liquid
`crystal display which display is a component part of the
`light trap;
`FIG. 4 is a perspective view of a ?uorescent plate for
`passive brightness ampli?cation which plate has an
`additional light source;
`FIG. 5 is a plan view of a quasi-analog display in the
`form of a large clock as in the sample embodiment of a
`display device constructed in accordance with the pres
`ent invention;
`FIG. 6 is a perspective view of a ?uorescent plate
`which is provided with a dichroitic mirror on one end
`surface and is in optical contact with a body which has
`a phosphorescent substance embedded therein.
`FIG. 7 is a perspective view of another embodiment
`of a ?uorescent plate having a phosphorescent layer;
`
`SONY_000670
`
`

`
`15
`
`20
`
`35
`
`4,142,781
`4
`3
`not-totally re?ected ?uorescent light or the light which
`FIG. 8 is an exploded view of an embodiment of the
`display device in accordance with the present invention
`is lost for the purpose of abbreviation is designated as a
`loss factor V and is determined by the following equa
`having a ?uorescent plate and a second ?uorescent
`plate acting as high pass ?lter;
`tion:
`FIG. 9 is a perspective view of yet another embodi
`ment of ?uorescent plate in accordance with the present
`invention having a phosphorescent layer disposed be
`tween the fluorescent plate and a high pass ?lter;
`FIG. 10 is a perspective view of an embodiment of a
`display device in accordance with the present invention
`with an additional collector plate;
`FIG. 11 is a graph illustrating the relation between
`re?ected intensity J r of unpolarized light which is di
`rected on an air-glass boundary surface as a function of
`the angle of incidence a;
`FIG. 12 is a graph illustrating the relation between a
`re?ected light intensity of J, of an unpolarized light
`which is entrapped in a glass body striking the glass-air
`boundary surface as a function of the angle of incidence
`11;
`FIGS. 13a-13d are four cross-sectional views of dif
`ferent structures for light decoupling or exit windows;
`FIGS. 14a and 14b illustrate a viewing angle 2 a
`which is obtained by a ratio x of the size of the exit
`window relative to the width of the light valve with
`FIG. 14a being a graph showing the relationship be
`tween the viewing angle and the ratio x;
`FIG. 15 is a graph illustrating the transmission curves
`of three commercially available plexiglass plates which
`?ouresce in different colors; and
`30
`FIG. 16 is a graph illustrating the emission curves of
`the plexiglass plates of FIG. 15.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The present invention utilizes a ?at or plane plexi
`glass plate having a thickness of a few millimeters and
`smooth surfaces. A ?uorescent material has been dis
`solved in this plate in such a concentration that, for
`example, the blue portion of incident daylight is fully
`absorbed. Furthermore, this plate is to have the four
`edge surfaces extending perpendicular to the plane of
`the plate and these edge surfaces are ideally light re
`?ecting so that no light can emerge at the edge of the
`plate. When light, such as daylight, strikes the surfaces
`of the plate, a portion will be re?ected and a second
`portion will enter into the plate. As illustrated in FIG.
`11, the relative re?ected intensity for J, for an unpolar
`ized light is indicated as a function of the angle a of
`incidence. When the light has an isotropic distribution
`such as daylight, approximately 82% of the intensity of
`the light will enter into the ?uorescent plate. For the
`remergence of the light from the plate, for example the
`?uorescent light transmitted in the green spectrum, the
`re?ection of the inner medium is now decisive and as
`illustrated in FIG. 12 as a function of the angle a of
`incidence. From these ?gures, it is seen that it can be
`calculated in good approximation, as if all the light
`which strikes the boundary surface under an angle not
`greater than am, (am, being the angle of total re?ection)
`leaves the plate, and the light of the remaining angular
`range remains in the plate as a consequence of a total
`re?ection. The angle of total re?ection follows from the
`relationship
`
`V: l — cosa.,a,="—_--——:2;l
`
`in this example, with n = 1.49, loss factor V = approxi
`mately 25%.
`The light emitted within the angular region of total
`re?ection, for example in the above example, is approxi
`mately 75% and is conveyed by a continual loss-free
`total re?ection in the plate. The average direction of
`propagation lying parallel to the plane of the plate.
`Thus, the ?uorescent plate functions as a light trap.
`The ?uorescent light captured in the ?uorescent plate
`as a consequence of total re?ection can now be caused
`to exit from the plate by re?ection at or from re?ecting
`or light scattering surfaces which are attached to the
`?uorescent plate. For abbreviation, such speci?c attach
`surfaces are designated as exit windows. A few exam
`ples of simple types of exit windows for decoupling
`light from the ?uorescent plate are depicted in cross
`section in FIGS. 13a-d.
`Neglecting dimension re?ection lossess and the un
`avoidable re-emergence losses, and assuming that no
`other losses are present in the plate, the “brightness
`ampli?cation factor”, i.e. the factor which indicates the
`increase of the illuminous density (surface brightness) of
`the ?uorescent plate exit windows vis-a-vis the illumi
`nous density of the non-?uorescing same color surface
`is essentially given by the ratio of relationship of the
`light absorbing surface of the arrangement to the total
`surface of the exit windows of the ?uorescent plate.
`The principles of the present invention combine the
`?uorescent plate as described above with an electro-op
`tical display device having light valves or shutters
`which are also called light gates. The display device is
`to be understood as a display in which the light valves
`or display elements are switched between a light trans
`missive condition and a light blocking or scattering state
`by the application of an electrical ?eld to transparent
`electrodes disposed on a thin layer of the electro-optical
`material. These displays often require the use of polar
`ized light and are provided with thin polarizing ?lms.
`An example of a known type of display is the liquid
`crystal display which utilizes a layer of liquid crystal
`material disposed between the transparent electrode to
`form a liquid crystal cell. In one type of liquid crystal
`display, the molecules of the liquid crystal layer are
`aligned parallel to each other and extend perpendicular
`to the surface of the cell so that a polarized light will
`pass through the cell unaffected. The application of an
`electrical ?eld to the transparent electrodes causes a
`scattering of the alignment of the liquid crystal mole
`cules which scattering will depolarize a polarized light
`passing through the cell. In such a liquid crystal device,
`the cell is arranged between cross-polarizers so that
`light will not pass through the cell until an electrical
`?eld is applied to the transparent electrodes to produce
`an area of the display to be light transmissive. In an
`other type of liquid crystal display device utilizes a
`“rotational cell” wherein the liquid crystal molecules
`are aligned parallel to the surfaces of the cell with the
`molecules adjacent one surface of the cell extending
`
`nsina = l
`10!
`
`wherein the index of refraction n = 1.49 for plexiglass
`42°. The portion of the
`and will produce an am,
`
`65
`
`SONY_000671
`
`

`
`4,142,781
`6
`5
`blocking condition, will block the ?uorescent light. In
`perpendicular to the direction of the molecules of the
`this arrangement, a display digit will appear bright on a
`other surface. In such a cell, the polarized light passing
`dark piece.
`through the cell will have the direction of polarization
`If the polarizers 6 and 7 are required and are neutral,
`rotated 90°. An application of an electric ?eld to the
`that is, they will polarize light of all wavelengths, then
`transparent electrodes of the cell will cause the mole
`the area of each polarizer should conform to the area of
`cules to be oriented perpendicular to the surface of the
`each of the light valves 5 so that the remaining surfaces
`cell so that a polarized light will pass through the cell
`of the display plate 4 is free of the polarizers and can
`without any rotation of the direction of polarization.
`transmit the incoming light to the ?uorescent plate 1a.
`In addition to combining the ?uorescent plate with
`However, if the polarizers 6 and 7 are not neutral, but
`the above known types of electro-optic display devices
`utilizing the effects of liquid crystals, the light trap of
`are two or more selective polarizers which will pass
`both polarizing directions for light of the range of the
`the present invention may be utilized with display de
`vices using the following types of electro-optical ef
`excitation light for - the ?uorescent screen, and only
`polarize the rest of vthe spectrum, the excitation light
`fects:
`passes the polarizers unweakened. In this manner, the
`(a) Linear and quadratic electro-optical double re
`entire display surface can be utilized as the light collec
`fraction effects in ferroelectric ceramic as dis
`tor surface and thus the amplification factor can be
`cussed in the above mentioned articles by G. H.
`signi?cantly increased.
`Haertling and C. E. Land, Journal of American
`A further modification of the invention permits an
`Ceramic Society, Vol. 54, 1971, page 1 and J. R.
`electrical switching between two different colors. To
`Maldonado and A. H. Metizler, Proceedings of the
`accomplish this, the’?uorescent plate contains a mixture
`IEEE, Vol. 59, 1971, page 368;
`of ?uorescent material for two different colors. For
`(b) Electrochromic effects, for example, a solid state
`example, the mixture creates both red and green ?uores
`?lm of W03 or M003 with a redox reaction in the
`cent light. If the ?uorescent plate transmits both red and
`boundary layer with an electrolyte such as H2804
`green light, it is only necessary to replace the polarizers
`as discussed in an article by S. K. Deb, Appl. Opt.
`6 in FIG. 1 by a combination of two selective polarizers.
`SuppL, Vol. 3, 1969, page 192; and
`One of the two polarizers is a horizontal polarizer but
`(c) Electro-optical scattering effects in ferroelectric
`passes green light unpolarized and the other polarizer of
`ceramics as discussed in an article by W. D. Smith
`the combination is a vertical selective polarizer which
`and C. E. Land, Appl. Phys. Lett., Vol. 20, 1972,
`will only pass red light unpolarized. After passage
`30
`page 169.
`through this polarizer combination, the ?uorescent
`An embodiment of a device utilizing the principles of
`light consists of horizontally polarized red light and
`the present invention is illustrated in FIG. 1. In this
`vertically polarized green light. Consequently, the en
`arrangement, an electro-optical device has a display
`tire arrangement only lets the green ?uorescent light
`plate 4 which is provided with individual triggerable
`pass through the light valves 5 when no voltage is ap
`segments or light valves 5. The electrode segments of
`plied thereto. However, when a voltage is applied, only
`each of the light valves permit a digital representation in
`red light will be able to pass through the segments of the
`accordance to a seven segment method. Arranged be
`light valves. The sameeffect will also come about by
`hind the display 4 is a ?uoresent plate 1a which is a
`substitution of the front polarizer with the described
`?uorescing synthetic material plate which has mirrored
`combination of two polarizers.
`end or edge surfaces 2 and ?uorescent light exit win
`If the emission of the ?uorescent plate 1a is already
`dows 3 which consist of mirrored notches in a plane
`polarized, the requirement of the rear polarizer 6 would
`surface of the plate 1a. The exit windows 3 have a shape
`be super?uous. The ?uorescent plate can be produced
`conforming to an electrode segment 5; however, their
`to have a polarized emission by means of embedding
`width is greater than the electrode segment width in
`?uorescent molecules. with their longitudinal axes in a
`order to compensate for a parallax between the elec
`preferential direction. The alignment of these molecules
`trode segments 5 and the exit windows 3. Behind the
`can be achieved with form-anisotropic ?uorescent mol
`?uorescent plate it is possible, if necessary, for another
`ecules, which were dissolved in the synthetic material
`light absorbing ?lm to be situated which ?lm must not
`plate, being oriented in accordance to a known method
`however be in optical contact with the ?uorescent
`by stretching the synthetic material plates in one direc
`plate. This ?lm will serve to make the ?uorescent plate,
`50
`tion.
`which naturally shows a characteristic color of its own
`A second embodiment of the present invention is
`transillumination, appear as “black” as possible and thus
`illustrated in FIG. 2. "In this embodiment, a ?uorescent
`provide a favorable in?uence on the display contrast. In
`plate 1b which will receive the ambient light is placed
`case the display plate 4 utilizes an electro-optical effect
`before the display plate 4 and is optically connected to
`which requires polarized light, polarizers 6 and 7 (indi
`the ?uorescent plate l‘a which has exit windows 3 by
`cated in broken lines) are attached on the front and back
`end segments 9 which have mirror end surfaces 2 to
`side of the display plate in the region of the light valves
`re?ect the ?uorescent light 180°. In this device, the
`5.
`viewer indicated by the eye 14 will look at the display
`4 through the front ?uorescent plate 1b. The ?uorescent
`light 8 will leave the exit windows 3 to pass through the
`light valves 5 which are selectively controlled to be
`either light transmissive or blocking. The ?uorescent
`plates 1a and 1b with the extension 9 on the three nar
`row sides of the display plate 4 thus constitute a sort of
`hood or envelope which receives the display plate 4. In
`this embodiment, polarizers 6 and 7 may be used if
`required by the particular type of display plate 4. In this
`
`The exciting light will pass from the front of the
`display in all directions through the display into the
`fluorescent plate. The ?uorescent light, which will be
`indicated in subsequent ?gures such as FIG. 2 by an
`arrow 8, will leave the ?uorescent plate through the
`exit windows 3 and go forward through the light valves
`65
`such as 5. However, only those electrode segments of
`the light valves 5 which have an electrical ?eld applied
`thereto to make them in a lighttransmissive state, will
`pass the light, and the other light valves, which are in a
`
`40
`
`SONY_000672
`
`

`
`5
`
`4,142,781
`7
`8
`embodiment there is an advantage that the ambient light
`which correspond to each one of the light exit windows
`can be better utilized since it does not pass through the
`3 with one light valve 5 for each exit window 3. A
`display plate 4 and in addition, neutral polarizers can be
`single light valve 5 for each of the inner and outer rings
`used in place of selective ones without any light loss.
`of exit windows can be triggered to represent the time
`The production of the hood-shaped fluorescent plate of
`in hours and minutes. The 120 elements or light valves
`this type is easily accomplished by an injection die cast
`of the display can be wired in a matrix fashion and can,
`ing process.
`therefore, be triggered statistically with little expense
`Another embodiment of the present invention is illus
`for the triggering electronics. Thus, a multiplex opera
`trated in FIG. 3. In this arrangement, a ?uorescent plate
`tion is not necessary.
`1b is attached in front of an electrically controllable
`FIG. 6 is a sample embodiment of a ?uorescent plate
`liquid crystal display 4 which is a component part of the
`with additional ?uorescent excitation by means of a
`light trap. The arrangement consists of the ?uorescent
`phosphorescing substance so that the device utilizing
`plate 1b having extensions 9 which are in optical
`the plate In can be used in the dark. The device consists
`contact with the edges of the display 4. The extensions
`of a ?uorescent plate 10 with mirrored surfaces 2 on
`9, as in the previous embodiment, are provided with
`three edges, with the fourth edge being free of any
`mirrored end surfaces 2 so that light is re?ected 180°
`mirrored surface. The ?uorescent plate 1a is in optical
`from the ?uorescent plate 1b into the display plate 4.
`contact with a synthetic material plate 17 in which
`The display device 4 consists of a liquid crystal display
`phosphorescing particles (not illustrated) with long
`or cell which contains a liquid crystal layer which be
`afterglow time, for example zinc sulphide, are embed
`comes light scattering under the in?uence of an electri
`ded. The synthetic plate 17 also has the three mirrored
`cal ?eld as discussed in the above mentioned article by
`end or edge surfaces. The contact surface between both
`Heilmeier, et al. As the electrode segments of each of
`plates 17 and 1a bears a dichroitic mirror 15 which will
`the light valves 5 have an electrical voltage applied
`pass the phosphorescent light designated by the arrow
`thereto, the dynamic light scattering in the liquid crys
`18; however, the mirror 15 will re?ect the ?uorescent
`tal layer will partially de?ect the ?uorescent light,
`light designated by the arrow 19. Thus, the phosphores
`which was traveling in the plane of the display 4, so that
`cent light 18 will enter the ?uorescent plate 1 to cause
`it can leave the liquid crystal cell. Since the diffusion or
`excitement of the ?uorescent light therein.
`scattering angles during the dynamic scattering are
`Another example of a ?uorescent plate 1a having
`relatively small, the ?uorescent light leaves the liquid
`additional ?uorescent excitation by means of a phos
`crystal display at an acute angle. For this emerging
`phorescent substance is illustrated in FIG. 7. In this
`?uorescent light to be visible to the eye of the viewer
`device, the ?uorescent plate 1a has the four edge sur
`14, it is again de?ected by a ?lm 10 which may be either
`faces mirrored and is provided with exit windows 3. A
`a light diffusing layer or a ?lm having a ?uorescent
`back surface 20 of the plate 10 is coated with a layer of
`material pigment layer. If the ?lm 10 is a ?uorescent
`phosphorescent particles 16 in such a way that the layer
`material pigment layer, it should not be excited to ?uo
`16 has no optical contact with the ?uorescent plate 10.
`rescence by ambient light entering from the front of the
`The part of the excitation light not absorbed by the
`display and is, therefore, covered with a ?lter ?lm 11
`?uorescent plate 10 is absorbed in the phosphorescent
`which only lets the ?uorescent light of the ?lm or foil
`particles of the layer 16 which absorption causes the
`10 pass through. This embodiment of FIG. 3 distin
`emission of a phosphorescent light 18 which can addi
`guishes itself by having no locally ?xed exit windows 3
`tionally excite the ?uorescent plate 1a.
`as in the previous mentioned embodiments. But rather,
`In some applications of the display device, such as
`the emergence of the ?uorescent light from the light
`illustrated in FIG. 1, it is possible that the ambient light
`trap which includes the display plate 4 is controlled by
`strikes not only the front surface of the display but also
`the display elements or light valves themselves. Thus,
`the back surface or side of the display. In order to be
`the display windows assume the position of the ener
`able to utilize the ambient light falling or striking the
`gized light valves. Therefore, this arrangement is partic
`back side of the display, a high pass ?lter is attached
`ularly suitable for matrix displays which have the elec
`behind the ?uorescent plate 1a. The high pass ?lter only
`trodes arranged in matrix patterns.
`passes the part of the spectrum which is absorbed in the
`In an embodiment of the invention illustrated in FIG.
`?uorescent plate 10. Due to the high pass ?lter, no
`4, the ?uorescent plate In which acts as a passive bright
`ambient light will strike the display from the rear and
`ness ampli?cation is provided with an additional light
`reach the viewer’s eye in front of the display and the
`source so that the display may be operated in a time of
`contrast of the display device is not reduced. The high
`darkness. The ?uorescent plate 1a has mirrored end
`pass ?lter can, for example, consist of an absorbing
`surfaces 2 and the ?uorescent light exit windows 3. At
`color ?lm which is suitably spectorial transmissive.
`one end surface, a rectangular recess 12 is provided. An
`55
`An example of an embodiment with a special high
`additional small light source 13, for example illumines
`pass ?lter is illustrated in FIG. 8. In this arrangement,
`cent diode (LED), is provided in the recess 12. Thus,
`the above mentioned high pass ?lter is replaced by a
`light from the source 13 will travel through the plate 1a
`second or supplemental ?uorescent plate 21 which has
`to cause the ?uorescent light for the display.
`A quasi~analog display in the form of a large clock is
`three mirrored edges or end surfaces 22. Solar cells
`60
`illustrated in FIG. 5 and is a further sample embodiment
`provided in a body 24 are attached to the non-mirrored
`of the electro-optical display device with a ?uorescent
`end or edge surface 23. The molecules embedded in the
`plate creating passive brightness ampli?cation. A ?uo
`supplemental ?uorescent plate 21 are selected in such a
`way that they absorb light of the desired range, for
`resoent plate la’ with a mirrored circumferential surface
`example, they form a high pass ?lter, but additionally
`2’ is provided with an inner and outer ring, respectively,
`of 60 light exit windows 3 which will display hours and
`emit light in the far red or near infrared spectrum which
`minutes, respectively. The electro-optical display will
`is the spectrum of light in which the solar cells are still
`have electrode segments or individual light valves,
`sensitive. As a result thereof, the solar cells can be sup
`
`45
`
`50
`
`65
`
`SONY_000673
`
`

`
`'10
`liters) and d = layer thickness. Full absorption of the
`main absorption band is easily achievable at a 1 mm
`layer thickness.
`’ 5. Chemical (photo chemical) stability of the ?uores
`cent material.
`
`LIGHT CONDUCTION:
`6. Re?ection capacity of the mirrored layers. As an
`illustrated, with a vapor deposited aluminum layer, the
`intensity re?ection capacity R = 0.913. After twenty
`re?ections, the intensity has diminished to 15% of the
`initial value. With a vapor deposited silver layer the
`intensity re?ection capacity R = 0.985. After twenty
`re?ections, the intensity has diminished to 73.5% of the
`initial value. R should be as close as possible to l.
`7. Absorption (and diffusion) of the synthetic material
`basic mass. For a 4 mm thick, clear plexiglass plate,
`which genuinely absorbs 1% of the light with a perpen
`dicular light incidence, the light would already have
`diminished to l/e of the initial intensity after a running
`time of 40 cm. Absorption is to be as small as possible.
`'8. Light diffusion or scattering as a consequence of
`surface roughness or surface contamination. As a ?uo
`rescent light is re?ected much more frequently from the
`boundary surfaces parallel to the plate plane than on the
`mirrored end surfaces, it is especially impo