Gas Discharge Panel With Photoconductive Material

Abstract

A data conversion and storage system incorporating a gas discharge panel having a light responsive element for sensing external light. When the panel is illuminated by projecting light onto the panel, the light responsive element combines with the electric field generated by an AC power source to cause selective glow discharges to occur. In this way, the image is converted by the panel to digital form with the glow discharges having a pattern corresponding to the image. After the image is removed, this information is stored until erased and also non-destructive transfer can be made to a readout device.

Description

This invention relates to improvements in gas discharge panels and also to data conversion and storage systems adapted for converting visual data to digital form and thereafter storing this information.

Gas discharge panels with electric memories are useful in providing visual displays of various data, such as numerals, letters, etc. These panels typically include a sealed gas chamber between a pair of dielectric members. Each dielectric member is backed by a conductor array and then a glass viewing plate. The conductor arrays have a transverse relative orientation and when an appropriate alternating operating potential is connected across selected conductors of each array, a glow discharge results in the chamber at the cross-points of these selected conductors. These glow discharges can thereafter be sustained with a reduced operating potential, which accounts for the panels memory ability. Typically this operating potential is derived both from a suitable write-in circuit and an AC source of sustaining potential. The write-in circuit selectively supplies the panel with write-in pulses of the proper phase and magnitude so that when summed with the sustaining potential, the total potential is sufficient to initiate the glow discharge. Thereafter, the write-in pulses can be removed because the sustaining potential is adequate to maintain the discharges.

In accordance with the invention a new and different gas discharge panel is now contemplated that also permits the selective write-in information with an external light.

Also contemplated is a novel gas discharge panel incorporating a light responsive provision that permits external light write-in and that can utilize the illumination from the glow discharge to sustain the discharge.

Further contemplated is a gas discharge panel in which the panel can be erased with an external light.

Another object is a system that converts visual data to digital form, that can store this digitized information until erased, and that provides a non-destructive readout of this digitized information.

Also an objective is a system utilizing a gas discharge panel which permits visual data to be projected onto a viewing face of the panel where the projected information is converted to digital form and then can be stored.

Other objectives include the provision of a gas discharge panel that requires less power, that is more reliable in operation, and that can be selectively turned on and off in several different ways to thereby render the panel more versatile in application, that incorporates provision for enhancing illumination, that affords highlighting and that provides a choice of colors of illumination.

The foregoing and other objects and advantages of the invention will be apparent from the following description and the accompanying drawings in which:

FIG. 1 is a perspective view of a visual data conversion and storage system incorporating the principles of the invention.

FIG. 2 is an exploded view of a gas discharge panel with the halves separated to show the conductor arrays;

FIG. 3 is a schematic view partially in section of a visual data conversion and storage system similar to the FIG. 1 system and includes a gas discharge panel with a photoconductive material;

FIG. 4 is a graph depicting the current flow in the panel's gas discharge chamber during one half cycle of operation;

FIG. 5 depicts an equivalent circuit for the FIGS. 1 and 3 gas discharge panels; and

FIGS. 6 and 7 are sectional views of modified gas discharge panels.

Referring first to the FIG. 1 data conversion and storage system, the numeral 10 denotes a gas discharge panel, which is positioned opposite an image projector 12. Visual information derived from the projector 12 is, in a way to be explained, converted by the gas discharge panel 10 to digital form and stored. Thereafter, this information can be readout by a readout device 14, shown against the side of the panel 10 and then erased.

The details of the panel 10 can be best observed in FIGS. 2 and 3. As shown in FIG. 3 the panel 10 has spaced apart support members or plates 16 and 18 which are formed of an electrically inert material, such as polished commercially available soda lime plate glass. The support plates 16 and 18 are also optically transparent so as to pass light and are capable strength wise of withstanding the pressures and the temperature changes to which the panel 10 will be exposed during operation.

The support plate 16 has a projection face 20 in front of the projector 12 on which is projected an image 22 shown as the letter Z in FIG. 1. Opposite the projection face 20, the support plate 16 has a conductor array 24 arranged as demonstrated in FIG. 2. The other support plate 18 has a viewing face at 26 and an opposite face with a conductor array 28. These conductor arrays 24 and 28 are connected to a source of AC power 29 and may have any suitable relative orientation; e.g., they may be at right angles relative to each other as they are shown in FIG. 2. Also, these conductor arrays 24 and 28 may, for certain applications, be in the form of a single conductor; e.g., a single conductive coating covering all of one or both of the support plate faces. These opposite conductor arrays 24 and 28 establish between the intersections of the individual and opposite conductors one or more cross-points 30 adequate in number for the intended use of panel 10. For example, when the panel 10 is operated in way to be explained, the selected cross-points 30 are illuminated so that glow discharges (shown as small dots in FIG. 1) will occur at these cross-points 30 so as to form the FIG. 1 outline of the letter Z.

The conductor arrays 24 and 28 may be formed on the support plates 16 and 18 by any well known process, such as photoetching, vacuum deposition, stencil screening, etc., or they may be in the form of wires or filaments. These arrays 24 and 28 should be made of a good current conducting material, such as copper, gold, silver, or aluminum and if optical transparency is required, transparent or semitransparent conductive materials, e.g., tin-oxide, and/or gold or aluminum may be used.

These conductor arrays 24 and 28 are insulated on the sides opposite the support plates 16 and 18 by dielectric members 31 and 32 respectively. These members 31 and 32 may be either a film or a coating and are optically transparent. The material of these members 31 and 32 should be thermally compatible with the material of the support plates 16 and 18.

Also the exposed surfaces of the dielectric members 31 and 32 should be relatively smooth and have relatively good charge trapping abilities. By way of example, the dielectric members 31 and 32 can be made of a glass material commercially known as Pemco, which has a high lead content and a low melting point. Also solder glass materials can be screened on the support plates 16 and 18 in the form of glass frit which is cured in place.

Spacers 34 separate the dielectric members 31 and 32 and establish the gap size for a sealed gas discharge chamber 36. These spacers 34 may be made of the same material as the dielectric members 31 and 32 and formed integral with one. The spacers 34 could in the alternative be made of solder glass and have a bead like structure. As beads, the spacers 34 could be located near the cross-points of the opposite conductors in the arrays 24 and 28, and suitably fused to one or both of the dielectric members 30 or 32. The number of beads used will be determined by the stress and the gap accuracy requirements of the panel.

The support plates 16 and 18, the dielectric members 31 and 32, and the spacers 34 are suitably connected and arranged so that the gas discharge chamber 36 can be filled with any well known inert gaseous discharge medium. The chamber 36 is then evacuated and sealed with an appropriate sealant 37, e.g., a high strength devitrified glass to maintain the gaseous mixture within the chamber 36 at the proper operating pressure. The gaseous mixture should be capable of being discharged upon application of a firing potential to selected conductors in each of the arrays 24 and 28 and produce an abundant supply of ions and electrons. Exemplary is a gaseous mixture consisting of neon gas as a major constituent and a small effective amount of at least one minor constituent selected from argon, krypton or xenon in an amount to provide a Penning mixture. A 90 percent neon and 10 percent nitrogen mixture is another example.

For purposes of demonStration only and without limitation, the panel 10 may have the conductors in the arrays 24 and 28 from 0.1 to 0.5 mils thick and from 2 to 6 mils wide, with center to center spacing of the conductors in the respective arrays 24 and 28 of about 20 to 30 mils. The thickness of the dielectric members 31 and 32 can be something less that 1 to 2 mils and the gap between the confronting faces of the dielectric members 31 and 32 may be about 4 to 9 mils. A gas pressure of 0.2 to 5 atmospheres within the chamber 36 can be used and, of course, the structural strength of the panel 10 will have to accomodate the selected pressure.

The foregoing description of the panel 10 is considered adequate for purposes of understanding the invention. If additional information is wanted, reference can be made to U. S. Pat. No. 3,499,167 to Baker et al, issued Mar. 3, 1970.

To render the panel 10 capable of write-in with an external light, a light responsive provision, which in the FIG. 3 embodiment is a photoconductive element 38, is incorporated in the panel 10. As is well known a photoconductor's conductivity increases with illumination and its effective resistance, decreases. This characteristic is utilized in a way to be explained.

The photoconductive element 38 can be a coating applied to the chamber side of the dielectric member 31 or it can be insulated from the chamber 36 by a dielectric material similar to that of the dielectric members 31 and 32. If wires are employed as the conductors they can be clad with the dielectric material of the dielectric members 31 and 32 and the photoconductive coating applied to the exterior. Also, the photoconductive material may be non continuous as long as proximate the cross-points 30, e.g., in the form of lines or dots 39 as designated 39 in FIG. 6, the shape of dots 39 can be other than circular; in fact, considerably varied. Any well known photoconductive material can be used, e.g., cadmium sulphide or cadmium selenide each with copper added to serve as an activator. The photoconductive material should have a spectral response that meets the operational requirements of the panel 10; i.e., the photoconductive material should properly change its conductivity with the type of external light used and whether the glow itself is to alter the conductivity will be determined by whether or not optical coupling is wanted. Also whether the photoconductive element 38 is applied to one or both of the dielectric members 31 and 32 will, as those versed in the art will appreciate, be determined by the circuit parameters required by the application of the panel 10.

The projector 12 can be of any commercially available type that is capable of projecting visual information onto the projection face 20 of the panel 10. The projector 12 illustrated in FIG. 3 includes an incandescent lamp 40 which illuminates a pair of lens 42. These lens 42 are between the incandescent lamp 40 and a picture slide 44. The letter Z image displayed in FIG. 1, is, of course, a digitized representation of the pictures on the slide 44. Opposite the picture slide 44 is a projector lens 46 maneuverable in the usual way to vary the size of image 22 and establish the proper focus. If required a suitable filter (not shown) can be included.

The readout device 14 functions to convert the image 22, which would be viewed on the face 26, into some form of information. For example, the readout device 14, could be a camera (not shown), or could include an array of light detectors 47 such as photodiodes or photoconductors, which control a printer 48 of some kind or a computer memory. There would be one light detector for each of the cross-points 30 of the conductors in the arrays 24 and 28 and they would individually sense the glow discharges at these cross-points 30.

The location of the readout device 14 can be varied to meet the requirements of different applications. As mentioned in FIG. 1, the readout device 14 is against the face 26 of the panel 10. The readout device 14 can be made movable relative to the face 26; e.g., by a tongue and groove type of track 50 or there may be a hinge like arrangement (not shown), which permits the readout device 14 to be swung out of the way, so that direct observation of the face 26 can be made. If for some reason it is preferred that the readout device 14 be remotely positioned from the panel 10, then an appropriate lens (not shown) can be used or as shown in FIG. 3, an array of light transmitting elements 52, e.g., of the fiber optic type, can be suitably connected by a plate 54 to each of the cross-points 30 of the conductor arrays 24 and 28 and transfer the illumination of the glow discharges to the remotely positioned readout device 14. At this remote station, the readout device 14 could have a corresponding array of light detectors which would develop the output that could be stored in the computer memory or used to drive the printer 48.

To operate the FIG. 3 system, the power source 29 is first turned on. Since the source 29 is connected across the arrays 24 and 28, a voltage will be applied across the gas discharge chamber 36 at each of the cross-points 30. Next the projector 12 is turned on to project the image 22 onto the face 20 of the panel 10. This illumination will energize the photoconductive element 38 at only the selected cross-points 30, i.e., those cross-points 30 in the path of the projected light rays that form the letter Z. Hence, at these cross-points 30, the resistance of the photoconductive element 38 will decrease. This resistance decrease will increase the voltage across the gap of the gas discharge chamber 36 at these cross-points 30 until the glow discharge level is reached. Then glow discharges will occur at these cross-points 30 so that the image 22 will be the digital representation of the letter Z from the picture slide 44.

To explain the reason for these glow discharges reference is now made to FIGS. 5 and 6. In the FIG. 5 equivalent circuit, the photoconductive element 38 is shown as a variable resistor and the dielectric member 31 and 32 and the gas discharge chamber 36 as capacitors. This equivalent circuit can be considered as representative of the circuits for each of the illuminated cross-points 30. When the photoconductive element's resistance decreases, there is less voltage dropped across the photoconductive element 38 but there is a corresponding increase in the voltage dropped across the chamber 36. Keeping in mind that a breakdown or a glow discharge cannot occur without a charge carrier, as this voltage across the chamber 36 increases, for instance, during the positive half-cycle of the AC source 29, the correspondingly increasing electric field applied to the illuminated cross-points 30 will force charge carriers, which may be loosely bound electrons, from the surfaces of the dielectric members 31 and 32. The applied electric field will accelerate these electrons and any free electrons present, to initiate collisions with the gas atoms and/or molecules and the dielectric member surfaces. This creates additional electrons and ions which are also accelerated by the electric field and ultimately there is an electron avalanche and a plasma discharge. The visual glow from this discharge occurs when the bound electrons in the gas atoms and/or molecules return to their normal ground states and emit photons of light. Upon discharge there is a flow of current across the chamber 36 and this appears as a spike 56 on the positive going side of the current trace in FIG. 4. This current spike 56 also corresponds to the projection of the image 22 on the panel face 20.

At or near the end of the positive half cycle of the AC source 29, the glow discharge extinguishes, but now charges have accumulated on the surface of the dielectric members 31 and 32 and are available for facilitating the discharge during the next half-cycle. Owing to the stored electrons for the initiation of the electron avalanche, the next discharge can be initiated with a lower voltage. For exemplary purposes only, if a peak to peak voltage of 400 volts was required to dislodge electrons from the dielectric member surfaces to start the first discharge, the additional electrons available after the first discharge can thereafter be accelerated with 300-350 volts peak to peak to initiate subsequent discharges.

Therefore, once the first discharge occurs this memory mechanism permits the projector 12 to be turned off and the panel 10 will continue to operate. Thereafter, the voltage of AC source 29 alone will be adequate to sustain the subsequent discharges. Because the photoconductive element 38 provides, in effect, a write-in voltage, which when summed with the source sustaining voltage, will generate the initial discharge for write-in purposes, it can be appreciated that the AC source 29 never has to provide more than one voltage. This feature eliminates the need for a complicated and expensive adjustable power source.

The cycle of operation continues at whatever frequency is chosen for the AC source 29. Frequencies of about 50 to 500 KC are suggested only for exemplary purposes. As can be appreciated at these frequencies, the extinguishing of the glow will not be discernable by the human eye but will appear as a continuous glow.

Once the panel 10 is operating and the information has been written-in, e.g., the letter Z image 22, readout can be made at any time with the external readout device 14. If it is preferred to make an internal readout, the FIG. 3 system could include any suitable electronic readout circuit 58, such as conventional, line scan or random access systems. If the latter readout circuit 58 is employed the side of the panel 10 including the support plate 18, the dielectric member 32 and the conductor array 28 does not have to be made of optically transparent material.

To erase the panel 10 the power source 29 is turned off. This removes the sustaining voltage, and consequently, all discharges will terminate. Also, erasure can be done by quenching, i.e., by retarding the radiation with radiation of another wave length, from the projector 12. For example, quenching can be done with infrared light since it tends to retard the photoconductivity of certain photoconductive materials.

The panel 10 may be operated in a slightly different way if preferred, by incorporating an appropriate write-in pulse generating source 60 in addition to the AC source 29. Write-in pulses from the source 60 could be applied to the entire panel 10, to one conductor at a time, or to one cross-point 30 at a time. Write-in would be effected only when a selected cross-point 30 had simultaneously applied to it a write-in pulse, the sustaining voltage from the source 29, and additionally is illuminated by light from the projector 12. Consequently without the write-in pulse, the sustaining voltage would not be adequate to produce a glow discharge even with the cross-point 30 illuminated with light. The sources 29 and 60, for these purposes, may be of the general type disclosed in application Ser. No. 699,170 to Johnson et al, filed Jan. 19, 1968, now U.S. Pat. No. 3,618,071.

There are different ways to erase when the write-in pulse source 60 is used. One way is as before, to turn off the source 29. Another way is to apply an erase pulse from a suitable source which could be the write-in pulse source 60. The erase pulse will be of such a phase and magnitude as to terminate the discharge at the selected cross-point 30 only if at the same time it is illuminated by external light, which can be provided by the projector 12. By this latter way a discharge is generated that is properly out of phase with the desired discharge so as to interfere with the memory mechanism by preventing the accumulation of charges. Therefore, the discharges are extinguished. These erase pulses could, as with write-in pulses, be applied to the entire panel 10 or to a conductor at a time or a cross-point 30 at a time.

The panel's ability to be erased by quenching with an external light of the appropriate wave length permits the direct addition and/or subtraction, or even correction, of information displayed on the panel. For example, if the visual image 22 includes several sentences, all or a portion of a sentence, or a word, or a part of a word may be erased by quenching and then if wanted replaced by writing-in the new information in the previously described way with the same projector 12 or any other type light source capable of providing light at the proper wave length and intensity.

The operation of the foregoing described panel 10 assumes that there is no optical coupling between the photoconductive element 38 and the discharge, i.e., there is no overlap of the spectral emission from the gas discharge and the spectral sensitivity of the photoconductor element 38 such that the illumination from the gas discharge maintains the photoconductive element 38 in its low resistance state. If an optical coupling is wanted, the photoconductive material and the gaseous mixture must be selected accordingly. When an optical coupling is employed, it will be appreciated that because of the assist from the glow the sustaining voltage can be less that without an optical coupling and therefore there will be a saving in power. The panel 10 with the optical coupling can be erased in any of the foregoing described ways.

It is possible with an optically coupled panel 10, depending on the dark decay characteristics of the photoconductive material, to turn off the power for a limited period of time and then turn it on before the photoconductive element 38 resistance has increased beyond a certain amount to refire the panel 10. This feature may be useful in some readout systems.

Additionally and with reference to FIG. 7, a luminescent material can be added to the panel for supplemental illumination. For instance, a phosphor known as P-31, which is zinc sulphide with a copper activator, can then be combined with the material of the photoconductive element 38, added as a continuous layer 62 or as noncontinuous lines, dots, etc. In FIG. 7, the panel which has been designated the numeral 10' is, except for the luminescent layer 62, the same in construction as the panel 10. The layer 62 is shown only on one side of the chamber 36 but as explained with respect to the photoconductive element 38 can, along with the photoconductive element 38, be on both sides.

In operation, the panel 10' will operate substantially the same as the panel 10. When light write-in is initiated, the resistance decreased by the photoconductive element 38 will cause the selective discharges. Photons of light from the discharges will then photoexcite the phosphor of the layer 62 and cause luminescence. This additional illumination at the selected cross-points 30 can be very helpful in high ambient light environments. Panel turn off or erasure can be achieved in the aforedescribed way. Also these additional illuminations can enhance the optical coupling if wanted.

As well understood by those versed in the art, the involved parameters, such as the gas and the luminescent material, are selected so that the radiation is of the proper wave length for photoexciting the material. The P-31 material for the layer 62 and the mentioned neon and nitrogen gaseous mixture have produced satisfactory results. Then too the color of the illumination can be varied depending on the choices of gases and luminescent materials.

In some instances a single material can be selected to serve both functions; i.e., both the photoconductive and the luminescent functions. The suggested P-31 material is capable to some extent of accomplishing this. Of course, this will be determined by the amount of luminescence desired as well as the photoconductive requirements that must be met by a particular application.

For various reasons, one may wish to highlight all or only a portion of an image on the projection face 20 of one of the panels 10 or 10'. This is accomplished by operating the panels 10 or 10' at above the discharge threshold so as to increase the intensification and can be done in different ways.

For example, if the panel 10 or 10' employs an electronic write-in provision, such as the mentioned write-in pulse generating source 60, to effect the glow discharges, an external light can be projected unto the face 20 at one or more of the cross-points 30. This will cause a reduction in the resistance of the photoconductive element 38 in the aforedescribed way and cause the intensification at the already illuminated cross-points 30, for the desired highlighting. Relating this to the letter Z in FIG. 1, one or more of its small dots can be selectively highlighted.

If light write-in is used, a supplemental light from a suitable source; e.g., the projector 12 or another similar projector or even an appropriate pen light, can also be projected unto the face 20 or the opposite face 26 at one or more of the illuminated cross-points 30. With the panel 10 or 10' being operated at the discharge threshold to attain the initial illumination, the supplemental light will further decrease the resistance of the photoconductive element 38 to, in effect, overdrive the gaseous mixture and produce the light intensification at these cross-points 30.

The highlighting ability of these panels 10 and 10' enables still further versatility by providing gray scale operation. Hence, in addition to the On and Off states, for a given voltage and light intensity, there is available a second On state that differs significantly in intensity from the first On state. For example, the image 22 can have its intensity increased by the overdriving effect and then its background, instead of being dark, illuminated but at a reduced intensity by operating this background at the discharging threshold, or the illumination of the background can be greater than that of the image.

From the foregoing, it will be appreciated the described visual data conversion and storage systems incorporating one of the gas discharge panels 10 or 10' can be printed or written-in, from an external source of illumination. When the information is written-in, an analogue to digital conversion is made, after which the digitized information is stored. Readout can be thereafter carried out without destroying the digitized information. Erasure can be accomplished in several ways, including the use of an external light source.

This invention is to be limited only by the following claims.

Claims

What is claimed is:

1. A gas discharge panel comprising housing means for a sealed gas chamber, a pair of conductor arrays arranged one on each of the opposite interior sides of said housing means; each array including at least one conductor having relative orientation to the other so as to provide one or more cross-points between the conductors in the opposite arrays, dielectric means arranged interiorally of the conductor arrays and providing surfaces defining at least a portion of the gas chamber, and photoconductive means arranged interiorally of the housing means in circuit with at least one of said conductor arrays and relative to the cross-points, said pair of conductor arrays, dielectric means, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said gas chamber providing capacitance in said current path and said photoconductive means being insensitive to the spectral emission from a gas discharge, being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and being operative in response to illumination of a selected cross-point from a source externally of said housing means when an operating voltage is applied thereto to increase the operating voltage across the gas chamber and cause a discharge within the gas chamber at the selected cross-point.

2. A gas discharge panel comprising a pair of support members having confronting spaced apart faces, each face having a conductor array arranged relative thereto, each array including at least one conductor having orientation relative to a conductor in the other array so as to provide one or more cross-points between the conductors in each array, a pair of dielectric members arranged between the support members and having the confronting surfaces thereof defining at least a portion of a gas chamber, and photoconductive means arranged between the support members in circuit with at least one of said conductor arrays and relative to the cross-points, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said gas chamber providing capacitance in said current path and said photoconductive means being insensitive to the spectral emission from a gas discharge, being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of the selected cross-point from a source externally of one of said support members when an operating voltage is also applied thereto, to increase the operating voltage across the gas chamber and cause a discharge within the gas chamber at the selected cross-point.

3. A gas discharge display and memory system comprising a gas discharge panel having a cavity therein, a pair of dielectric members arranged within the cavity and constructed so that surfaces thereof define at least a portion of a sealed gas chamber therebetween, and a pair of conductor arrays one on each side of the gas chamber and spaced therefrom by one of the dielectric members, the arrays each including at least one conductor oriented relative to a conductor in the other array so as to provide one or more cross-points between opposite arrays; a power source connectible to the arrays so as to apply an operating voltage across the conductor arrays; and photoconductive means arranged within said cavity in circuit with at least one of said conductor arrays and relative to one of the conductors arrays, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said gas chamber providing capacitance in said current path and said photoconductive means being insensitive to the spectral emission from a gas discharge, being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of said panel to increase the operating voltage across the gas chamber and cause a discharge at the selected cross-point.

4. A data storage and conversion system comprising, in combination, a gas discharge panel having a sealed gas chamber, a pair of conductor arrays arranged one on each of the opposite sides of the gas chamber, each array including at least one conductor having relative orientation, so as to provide one or more cross-points between the conductors in each array, dielectric means providing surfaces defining at least a portion of the gas chamber, and photoconductive means arranged within said panel in circuit with at least one of said conductor arrays and relative to one of the conductor arrays, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said gas chamber providing capacitance in said current path and said photoconductive means being insensitive to the spectral emission from a gas discharge, being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of said panel when an operating voltage is also applied to the selected cross-point to increase the operating voltage across the gas chamber and cause a discharge at the selected cross-point; a power source connectible to the conductor arrays so as to apply the operating voltage across the conductor arrays; and write-in means for illuminating the photoconductive means at the selected cross-point to cause a discharge.

5. A gas discharge display and memory system comprising, in combination, a gas discharge panel having a sealed gas chamber, a pair of conductor arrays arranged one on each of the opposite sides of the gas chamber, each array including at least one conductor having relative orientation to the other so as to provide one or more cross-points between the conductors in each array, dielectric means providing surfaces defining at least a portion of the gas chamber, and photoconductive means arranged within said panel in circuit with at least one of said conductor arrays and relative to one of the conductor arrays, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said gas chamber providing capacitance in said current path and said photoconductive means being insensitive to the spectral emission from a gas discharge, being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of said panel when an operating voltage is also applied to the selected cross-point to increase the operating voltage across the gas chamber and cause a discharge at the selected cross-point, a power source connectible to the conductor arrays; write-in means for energizing selected cross-points for effecting a visual image on the panel of one light intensity; and highlighting means for energizing certain cross-points to cause illumination of another light intensity on the panel.

6. A gas discharge panel comprising a pair of support members having confronting spaced apart faces, each face having a conductor array arranged relative thereto, each array including at least one conductor having orientation relative to a conductor in the other array so as to provide one or more cross-points between the conductors in each array, a pair of dielectric members arranged between the support members, and photoconductive means arranged on the surface of at least one of the dielectric members, the surface thereof defining at least a portion of a gas chamber, said photoconductive means being in circuit with at least one of said conductor arrays and proximate the cross-points, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said dielectric members and gas chamber on opposite sides of said photoconductive means providing capacitance in said current path and said photoconductive means being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of one of said support members when an operating AC voltage is also applied through the conductors at the selected cross-point, to increase the operating voltage across the gas chamber at the selected cross-point and cause a discharge within the gas chamber at the selected cross-point only.

7. A gas discharge panel comprising housing means for a sealed gas chamber, a pair of conductor arrays arranged one on each of the opposite interior sides of said housing means; each array including at least one conductor having relative orientation to the other so as to provide one or more cross-points between the conductors in the opposite arrays, dielectric means arranged interiorally of the conductor arrays, and photoconductive means arranged interiorally on the surface of the dielectric means, the surface thereof defining at least a portion of the gas chamber, said photoconductive means being in circuit with at least one of said conductor arrays and proximate the cross-points, said pair of conductor arrays, dielectric means, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said dielectric means and gas chamber on opposite sides of said photoconductive means providing capacitance in said current path and said photoconductive means being capable of increasing its conductivity and decreasing its effective resistance when subject to illumination and being operative in response to illumination of a selected cross-point from a source externally of said housing means when an operating AC voltage is applied through the conductors at the selected cross-point to increase the operating voltage across the gas chamber at the selected cross-point and cause a discharge within the gas chamber at the selected cross-point only.

8. A gas discharge panel as described in claim 1, wherein the photoconductive means includes luminescence means operative in response to illumination from the discharge to emit light at the selected cross-point.

9. A gas discharge panel as described in claim 1, further including luminescence means arranged relative to the gas chamber so as to in response to illumination from the discharge at the selected cross-point emit light at the selected cross-point.

10. A gas discharge display and memory system comprising, in combination, a gas discharge panel having a sealed gas chamber, a pair of conductor arrays arranged one on each of the opposite sides of the gas chamber, each array including at least one conductor having relative orientation to the other so as to provide one or more cross-points between the conductors in each array, dielectric means insulating said conductor arrays from said gas chamber, and photoconductive means arranged within said panel on at least one surface of said dielectric means and providing at least one surface defining at least a portion of the gas chamber, said photoconductive means being in circuit with at least one of said conductor arrays and proximate one of the cross-points, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said dielectric members and gas chamber on opposite sides of said photoconductive means providing capacitance in said current path and said photoconductive means being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of said panel when an operating voltage is also applied through respective conductors to the selected cross-point to increase the operating voltage across the gas chamber at the selected cross-point and cause a discharge at the selected cross-point, an AC power source connectible to the conductor arrays; write-in means for energizing selected cross-points for effecting a visual image on the panel of one light intensity; and highlighting means for energizing certain cross-points to cause illumination of another light intensity on the panel.

11. A gas discharge display and memory system as described in claim 10 wherein the write-in means and the highlighting means both include a light source.

12. A gas discharge display and memory system as described in claim 10 wherein the highlighting means includes a light source for energizing the certain cross-points so that the background of the visual image has a light intensity different from that of the visual image.

13. A gas discharge display and memory system comprising a gas discharge panel having a cavity therein, a pair of dielectric members arranged within the cavity with photoconductive means arranged on the surface of at least one of said dielectric members, the surface thereof defining at least a portion of a sealed gas chamber, and a pair of conductor arrays one on each side of the gas chamber and spaced therefrom by one of the dielectric members, the arrays each including at least one conductor oriented relative to a conductor in the other array so as to provide one or more cross-points between opposite arrays; and an AC power source connectible to the arrays so as to apply an operating voltage across the conductor arrays; said photoconductive means being arranged within said cavity in circuit with at least one of said conductor arrays and proximate one of the conductor arrays, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said dielectric members and gas chamber on opposite sides of said photoconductive means providing capacitance in said current path and said photoconductive means being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of said panel to increase the operating voltage across the gas chamber at the selected cross-point and cause a discharge within the gas chamber at the selected cross-point only.

14. A gas discharge display and memory system as described in claim 13, wherein the photoconductive means is also operative in response to the illumination from the discharge to sustain the discharge.

15. A gas discharge display and memory system as described in claim 13, wherein the photoconductive means includes luminescence means operative in response to illumination from the discharge to emit light at the selected cross-point.

16. A gas discharge display and memory system as described in claim 13, further including luminescence means arranged relative to the gas chamber so as to in response to illumination from the discharge at the selected cross-point emit light at the selected cross-point.

17. A data storage and conversion system comprising, in combination, a gas discharge panel having a sealed gas chamber, a pair of conductor arrays arranged one on each of the opposite sides of the gas chamber, each array including at least one conductor having relative orientation, so as to provide one or more cross-points between the conductors in each array, dielectric means insulating said conductor arrays from said gas chamber, and photoconductive means arranged within said panel on the surface of said dielectric means and providing at least one surface defining at least a portion of the gas chamber, said photoconductive means being in circuit with at least one of said conductor arrays and proximate one of the conductor arrays, said conductor arrays, pair of dielectric members, gas chamber and photoconductive means being arranged in series electrically to provide a current path at each of said cross-points, said dielectric members and gas chamber on opposite sides of said photoconductive means providing capacitance in said current path and said photoconductive means being capable of increasing its conductivity and decreasing its effective resistance when subjected to illumination and operative in response to illumination of a selected cross-point from a source externally of said panel when an operating voltage is also applied through respective conductors to the selected cross-points to increase the operating voltage across the gas chamber at the selected cross-point and cause a discharge within the gas chamber at the selected cross-point; an AC power source connectible to the conductor arrays so as to apply the operating voltage across the conductor arrays; and write-in means for illuminating the photoconductive means at the selected cross-point to cause a discharge.

18. A data storage and conversion system as described in claim 17, wherein the photoconductive means is also operative in response to the illumination from the discharge to sustain the discharge.

19. A data storage and conversion system as described in claim 17, and further including erase means extinguishing the discharge.

20. A data storage and conversion system as described in claim 19, wherein the erasing means includes a source of illumination for selectively quenching a discharge.

21. A data storage and conversion system as described in claim 17, wherein the write-in means includes means projecting an illuminated image on the panel to cause discharges at selected cross-points to provide a corresponding image in digitized form.

22. A data storage and conversion system as described in claim 21, and further including read-out means including light detecting means associated with each cross-point for sensing illumination therefrom and erase means extinguishing the discharge.

23. A data storage and conversion system as described in claim 17, and further including readout means responsive to the discharge.

24. A data storage and conversion system as described in claim 23, wherein the read-out means is moveably positioned proximate the panel and includes light detecting means associated with each cross-point for sensing the illumination therefrom.

25. A data storage and conversion system as described in claim 23, wherein the read-out means is positioned remotely of the panel and includes light conducting elements associated with each cross-point for transferring illumination therefrom to the read-out means.