DE1132182B - Electroluminescent device - Google Patents

Description

Electroluminescent Device The invention relates to electro-optical devices with an electroluminescent matrix and in particular combinations of an electroluminescent matrix with tiner access unit.

Known devices with an electroluminescent matrix consist of small ones Electroluminescent electrodes that are between a large number of columns and rows thin conductor are layered. Usually one end of each conductor is exposed and is provided with connections. The connections are often in the form of contact surfaces designed for sliding contacts, or they are connected to the terminals of a sliding contact switch, an electrical shift register or other devices switched on and thus result in a combined matrix access unit.

Making the connections is a difficult problem because the conductors generally consist of an extremely thin metal coating that is vacuum applied to a surface in the form of a pattern of parallel, closely spaced conductors or painted on the surface in the form of thin, narrow strips will. In all cases it is extremely difficult to make sufficiently good electrical connections to such thin and delicate conductive coatings. The difficulties are exacerbated by the fact that the electrical connections to the conductors of the matrix still have to be connected to certain individual excitation units. This makes such devices sensitive, cumbersome and therefore uninteresting for a large number of applications.

It is already an arrangement of photosensitive and electrolunescent Cells known in which a light spot along a row of electroluminescent cells is forwarded from one cell to the next so that each cell lights up, while the previously excited one goes out again.

The present invention aims to eliminate the described shortcomings of the known arrangements and to provide an electro-optical device with an electroluminescent matrix consisting of two crossing groups of conductors, between the crossing points of which electroluminescent material is attached, and with access circles for selecting the crossing points to be excited. It recommends to the fact that the conductors of each group are connected to an excitation voltage across photosensitive elements can not bring the crossing points to light up as long as the photosensitive elements remain unexposed, and that the access circuits include electroluminescent cells, such that each one cell per is assigned radiation-wise to one of the photoconductive elements.

In one embodiment of the invention, the access loop exists for the electrolunescence niatrix of radiation-generating and radiation-sensitive Elements that create a light spot that moves along a predetermined path, moved a controlled amount. The light emitted in this way by the access circle triggers a second group of radiation-sensitive elements that are electrically connected to the matrix. This second group of elements in turn serves as a switch that allows the application of an excitation voltage to selected parts of the matrix effect and thus generate controlled lunar dense spots.

The access circle has a multitude of levels, each of which has a specific Have assignment to the matrix. Each stage comprises a parallel connection of one radiation-sensitive and radiation-generating element in series with a further radiation-sensitive element is connected.

In this way, voltages are applied to the stages of the assigned devices that a radiation-generating element of a selected level is activated. the Selection is accomplished by taking part of an energized element of one Stage emitted light onto a light-sensitive element of a subsequent stage is directed so that this stage ignites, and a subsequent enlargement a radiation-emitting element of the applied voltage this Level excited. The element excited in this way emits radiation to the previous stage, to switch off the excited element there. Through this selective application of tension the various levels are located along the associated access units moving light spots generated.

The associated access units are with respect to a second Group of radiation-sensitive elements in the matrix arranged so that they Can transmit light. Each element of this second group serves as a switch for a given conductor of a plurality of arranged in columns and rows Ladders. These conductors are on opposite sides of an electro-fluorescent material arranged and thus form an electroluminescent matrix known per se. Which moving light spots shining on the radiation-sensitive elements of the matrix excite these elements and establish a connection between an exciting voltage source and a selected portion of the electroluminescent material such that the selected ones Parts are excited to glow.

The use of radiation-sensitive elements as switches between an exciting voltage source and those arranged in columns and rows Conducting an electroluminescent matrix provides a compact unit for access to the intersection points of the matrix when combined with the assigned Access circuits are used whose preselected light-generating elements radiation hand over.

Since all the required sub-elements are made using known manufacturing processes for vacuum coatings are to be produced, the entire unit can be placed on a suitable, transparent base, so that special electrical connections between the matrix and the assigned access units can be omitted.

A better understanding of the invention can be obtained from the following detailed description together with the drawings; It shows Fig. 1 is a schematic arrangement, partly in block diagram, the combination of a Elektrolumineszenzmatrix and an access unit as an embodiment of the invention, Fig. 2A and 2B are exploded views of constructive details of a portion of an associated Zugriffseinhei.t, which in the embodiment of Fig. 1 can be used, Fig. 3 constructional details of a portion of the associated access unit and a cross point portion of the matrix, Fig. 4, 5 and 6 show three views of the construction arrangement of a part of the combined matrix access unit, which is shown schematically in FIG. 1.

According to FIG. 1 , the combination shown consists of the electroluminescent matrix 10 and the row and column-assigned access units 40 and 40 ', respectively. The access unit 40 of FIG. 1 is composed of a number of stages which use radiation-sensitive and radiation-emitting elements. Only four levels are shown for purposes of illustration, although any desired number can be used to advantage. Each stage consists of a radiation-sensitive or photoconductive element in series with a parallel connection of a further photoconductive element and a radiation-emitting or electroluminescent element. It is known that electroluminescent elements which can be made from a material such as zinc sulfide phosphor can emit visible or near-visible radiation.

The photoconductive elements, which - as is known - can be made from a material such as crystalline cadmium sulfide, are susceptible to the radiation emitted by the electroluminescent elements in order to reduce the normally high impedance of the photoconductor.

The switching function of the access unit 40 assigned to a row can best be explained by assuming that the switch 44 is closed and that the voltage source b 52 is thus connected to the various stages of the access unit 40 in parallel. However, the voltage source 52 supplies a voltage which alone is not large enough to excite any of the electroluminescent elements 42, 46, 50 or 54, so that no function is carried out at this time.

When energization of the in-line access unit 40 is desired, a small amount of light is applied briefly to the photoconductive element 41 from an external source 56. The external source can advantageously be a lamp, an electroluminescent element or some other radiation-generating means. It is well known that a photoconductor in the presence of radiation of a certain wavelength and intensity to which it is sensitive provides a low impedance to a current and, conversely, a photoconductor in the absence of such radiation gives a high impedance to the current. Assuming that the radiation from the source 56 is of suitable strength and wavelength and is incident on the photoconductive element 41 on the light path 57 , then the impedance of the element is reduced to a low value. As a result, a voltage is applied from the source 52 to the electroluminescent element 42, which is thereby excited to glow darkly. The electroluminescent element 42 in turn radiates onto the photoconductive elements 41 and 45 on the light paths 58 and 59, respectively. In addition, the electroluminescent element 42 radiates on the light path 70 onto another photoconductor 13, the purpose of which will be explained in detail later. The above-mentioned, only weak radiation of the electroluminescent element 42 reduces the resistance of the photoconductor 41 by a small amount; however, no further function would now result without a higher voltage being applied to the various stages of the access unit 40.

The higher voltage is generated at a desired point in time by briefly opening the switch 44, which connects the voltage source 48 in series with the voltage source 52 , whereby the voltage on the electroluminescent element 42 is increased by an amount sufficient to brighten the element To cause annealing. As already mentioned, the radiation generated by the element 42 is fed to the photoconductive elements 41 and 45 on the light paths 58 and 59. This radiation returned on the light paths 58 and 59 tries in a feedback manner to put the photoconductive elements 41 and 45 into a state of even lower impedance. Corresponding to the normal impedance characteristics of a photoconductor, there is a large change in the impedance with a relatively small change in the radiation directed onto the photoconductive element. Therefore, element 42 emits enough light onto the series-connected photoconductive element to make the resistance of that element so small that there is sufficient voltage across electroluminescent element 42 to keep that element glowing brightly. This feedback radiation is sufficient to keep the photoconductor-electroluminescence series combination 41, 42 in the "on" state after the switch 44 is closed, whereby the voltage source 48 is short-circuited and only the voltage source 52 voltage to the first stage of the Access unit 40 supplies.

The function described so far results in the first stage in the "on" state and the other stages in the "off" state until the switch 44 is actuated again. Before the switch 44 is actuated, however, the radiation from the element 42 on the light path 59 to the photoconductor 45 has applied a sufficiently high voltage from the source 52 to the electroluminescent element 46, which is thus caused to glow darkly . At the desired point in time, the switch 44 can again be briefly opened in order to apply a voltage from the two voltage sources 48 and 52 to the steps of the access unit. This high voltage causes the electroluninescence element 46 to glow brightly, which radiates onto the photoconductive elements 43, 45 and 49 on the light paths 61, 62, 63.

Since the photoconductive element 43 is connected in parallel with the electroluminescent element 42, the radiation supplied on the light path 61 reduces the impedance of the photoconductive element 43. This drop in impedance reduces the voltage across the photoconductive element 43 and consequently on the electroluminescent element 42, which results in a reduction in size of the excitation severity through the electrolunrinescence element 42 results. This reduction in the excitation current causes a substantial reduction in the radiation emitted by the element. Thus, a reduction in the radiation fed back onto the series-connected photoconductor 41 is brought about, and an increase in the impedance of the photoconductor 41 in turn results in a further decrease in the radiation from the electroluminescent element 42. This feedback effect continues until the electroluminescent element is completely extinguished.

As mentioned earlier, the electroluminescent element 42 radiates on the light path 59 onto the photoconductive element 45. The termination of the luminescence of the element 42 would in turn result in an increase in the impedance of the photoconductive element 45, if not a feedback function between this element and the electroluminescent element 46 would exist. In other words, the photoconductive element 45 is placed in the saturated impedance state by the radiation on the light path 62 from the electroluminescent element 46; so there is no significant influence on the photoconductive element 45 due to the lack of radiation on the light path 59 because of the termination of the luminescence of the electroluminescent element 42.

Level 1 of the access unit 40 is now in the "off" state, and level 2 in the "on" state. This state continues until the switch 44 is again briefly opened in order to switch the second stage into the “off” state and the third stage into the “on” state. The above-described function can then be repeated at desired time intervals by simply operating the switch 44 selectively.

The other associated access unit 40 'operates in the same way Manner as described above for the unit 40 and consists of similar parts, which are marked with dashed digits.

The access units 40 and 40 'are arranged to be optically connected to the electroluminescent matrix unit 10 , which is advantageously of the type known per se which utilizes painted or vacuum deposited columns and rows of conductors defined by an adjacent layer or Electrodes of an electroluminescent material are separated. The matrix formed in this way is indicated schematically by the horizontal rows 11 and the vertical columns 12. The electroluminescent layer, which is arranged close to and between the rows and columns 11 and 12, forms a multiplicity of crossing points 28 to 39. The row and column conductors 11 and 12 have photoconductive elements 13, 15, 17, 19 and 14, 16, 18. A common voltage source 25 is connected to the row and column conductors 11 and 12 via these photoconductive elements.

In the absence of radiation, these photoconductive elements are in the high impedance state, thus preventing the application of voltage from the source 25 to any part of the electroluminescent matrix 10. This state results when both the row and column access units are not energized. The optional excitation of the row and column assigned access units generates light spots which shine on individual photoconductive elements of the matrix and reduce the imi) edance of these elements and thus allow an application of voltage from the source 25 to opposite sides of the electroluminescent layer.

It should be noted that the row and column assigned access units 40 and 40 'must excite two specific photoconductive elements that have a specific Define the crossing point before a voltage is applied to both sides of the electroluminescent element is applied and causes it to glow brightly. For the sake of clarity Imagine that the second stage of the row access unit 40 is in the "on" state and the remaining stages are in the "off" state while at the same instant the first stage of the column access unit 40 'is in the "on" state and the remaining Levels are in the "off" state. Then there is an illuminated state of the Elements 42 'and 46 in units 40' and 40, respectively.

The radiation emitted by the electroluminescent element 46 is transmitted to the photoconductive element 15 via the light path 71 . At the same instant, the radiation emitted by the excited electroluminescent element 42 ′ is transmitted to the photoconductive element 18 via the light path 70 ′ in the column access unit. The photoconductive elements 15 , 15 and 18 are designed so that the radiation received reduces its normally high impedance to a low impedance. This reduction in impedance makes it possible to apply an excitation voltage from the voltage source 25 to both sides of the electroluminescent element 33 and therefore causes this element to glow brightly.

During the next operation, the switch 44 remains closed and the switch 44 'is briefly opened. The element 46 in the row access unit would continue to light up, while the element 42 'in the column access unit would be extinguished and the element 46' would light up in the manner described above. During this process, the photoconductive element 15 in the row would remain in the low impedance state because of the radiation transmitted by the electroluminescent element 46 on the light path 71. However, the photoconductive element 18 of the column would revert to the high impedance state due to the lack of radiation since the element 42 'is in the deenergized state. The energization of the electroluminescent element 46 'would bring the photoconductive element 16 into the state of low impedance so that the voltage source 25 can apply a voltage to both sides of the electroluminescent crosspoint 32 and thus causes a glow in this crosspoint. The cross point 33 would no longer shine with the previous brightness, since the photoconductive element 18 is in the high impedance state and thus switches off the voltage applied to the element by the voltage source 25.

From this it can be seen that by optional. Actuation, switches 44 and 44 'can energize any particular group of electroluminescent elements in the matrix. Therefore, the desired information is supplied to the column and row access units, and the information is identified by actuation or non-actuation of the access switches 44 and 44 '; the electroluminescent matrix 10 , by virtue of the selective switch actuation, can have various parts which glow in succession so that any desired visual pattern can be designed.

FIGS. 2 A and 2 B show constructive details of a portion of the row associated Züigriffseinheit, and they show details of the upper and lower side of the part of the access unit. Certain elements of FIGS. 2A and 213 correspond to the elements of the circuit of FIG. 1. Where there is a match, the elements are labeled in the same way.

In Fig. 2A , the top surface of a glass plate 90 is covered with transparent, electrically conductive pads 91 and 92 . The electroluminescent phosphor layers 142 and 146 and an electrically conductive electrode 93 are shown in an exploded view above the transparent, conductive layers 91 and 92. The electroluminescent overlay 142 is slightly larger than the clear conductive overlay 91 while the outer conductive electrode 93 is slightly smaller than the electroluminescent overlay 142 to avoid any short circuit between the conductive electrodes if the elements were brought together in normal use.

Fig. 2B shows, in an exploded view, the elements of Fig. 2A compressed in their normal position and with the lower surface rotated 180 ' about the axis X-X, as shown, against the viewer so that the elements of the lower side of the , 90 can be seen from Fig. 2 A now in an exploded view glass plate. It will then be easy to see that the clear conductive pads 91 and 92 are laid around the edge of the glass plate 90 in the rectangular zones as shown. The other elements 95 and 96 which lie in the plane defined by the clear conductive pads 91 and 92 are also clear conductive pads. The dashed lines emanating from these clear conductive pads indicate the locations where the subsequent photoconductive elements would rest in the normal compressed cross-section. For example, as shown, the conductive electrode 97 is followed by FIG the photoconductive elements 141 and 145 which, as indicated by the dash-dotted lines, are applied to the transparent, conductive pads 91 and 92. Similarly, the conductive electrode 98 is applied to the photoconductive element 143 and the conductive electrode 99 to the photoconductive elements 113 and 115, and they would then be brought into the position indicated by the chain lines.

The supports can advantageously be composed of known materials. For example, the clear conductive pads 91, 92, 95 and 96 can be made of tin oxide. The electroluminescent layers 142 and 146 can be made from either a dielectric suspension of electroluminescent phosphor or from various well known crystalline films. The conductive electrodes can advantageously be formed from some well known materials such as a silver plating.

The arrangement and operation of the above-described portion of the associated access unit can be more easily understood with reference to FIG. 3. This shows the exploded elements of FIG 99 are shown as electrical conductors for the sake of clarity. In addition, the intersection points 28 and 31 of the electroluminescent matrix are shown, which are defined by the part of the electroluminescent overlay 101 which is layered between the transparent, conductive electrodes 95 and 96 and a second conductive electrode 26 , which is connected to the column-associated access unit 40, which is only partially shown ' connected is. The other elements correspond to elements of Figures 2A and 2B and are labeled similarly.

3 shows the electroluminescent overlay 142 sandwiched between the conductive electrode 93 and the transparent, conductive overlay 91. The conductive electrode 93 is connected to the voltage source 52 via the line 53 connected to the line 51 and therefore applies a voltage to one side of the electroluminescent layer 142 connected in parallel. The other side of the voltage source 52, which contains the voltage source 48 and the switch 44 connected in parallel, is connected via the line 50 to the conductive electrode 97 , which in turn forms a series circuit with the photoconductive element 141 via the conductive pad 91 and one from the photoconductive Element 143 and the electroluminescent coating 142 represents parallel circle formed. In AB of radiation from the external source 56 being, as described previously, be the photoconductive elements 141 and 143 hcher impedance state, so that the Elektroluminesze # .- # zatif12, oc 142 is isolated from the voltage source 52nd

When commissioning is desired, light from the external source 56 is directed onto a portion of the photoconductive element 141 via the light path 57 and the radiation lowers the impedance of the photoconductive element 141 somewhat. This results in a conductive path from the electrode 57 through the photoconductive element 141 to the transparent conductive support 91. The voltage source 52 applies a closed switch 44 a voltage to the top Elektrolumineszenzauflage. 142 via the above-mentioned route; namely the closed switch 44, the line 50, the electrode. 97, the reduced resistance of the photoconductive element 141 and the transparent, conductive layer 91. If one side of the voltage source 52 with the upper part of the luminescent layer 142 and the other side of the voltage source 52 with the lower layer side of the element 142 can be connected to the lines 51, 53 and the conductive electrode 93 are connected, the electroluminescent element 142 will only shine weakly. The radiation emitted by the weakly glowing electroluminescent layer 142 is transmitted through the transparent layers 91 and the glass plate 90 and shines fully onto the photoconductive elements 113 and 141 and onto part of the photoconductive element 1.45. However, this small amount of light is insufficient to completely reduce the impedance of this element - and no further function would now take place without a higher voltage being applied to the electroluminescent element 142.

The higher voltage is created at a desired moment by briefly opening the switch 44, which connects the voltage source 48 in series with the voltage source 52 and thereby increases the voltage on the electroluminescent element 142 by an amount sufficient to make the cell glow brightly cause. As mentioned earlier, the photoconductive element 141 and the electroluminescent element 142 are in a de-attenuating feedback relationship that is sufficient to keep the series circuit thus formed in a stable "on" state after the switch 44 is closed and the voltage source 48 is closed shorted.

After the operation thus described, the electroluminescent element 142 glows brightly and is sufficient to lower the normally high impedance of the photoconductive element 113 to a low value. Voltage source 25 will therefore apply a voltage across line 21, conductor 99, low impedance element 113, transparent conductive overlay 96 and conductive overlay 103 to one side of electroluminescent overlay 101 .

As described earlier, it is necessary to apply a voltage of a suitable level to both sides of the electroluminescent charger a., E 101 in order to make them glow. In the course of the function described up to this point, a voltage has only been applied to the lower side of the electroluminescent layer 10 1 . In a manner similar to that described above, the 'column access unit 40', which is also located on the glass plate 90 , lowers the impedance state of a second input photo element and therefore connects the voltage source 25 to dc-1-conducting electrics 26. It is closed recognize. that the voltage source 25 is then connected to the upper and lower side of the electroluminescent layer 101 , and the intersection point 28, which is formed by the two conductive layers 26 and 103 , is excited to glow. portion shown at 3 makes the complete operation of the combined matrix access unit is clear from FIGS. 4, 5 and 6 produced. FIG. 6 shows a four-stage section, the access unit associated with the rows, part of the column access unit and three crossing points of the electroluminescent matrix which are old arranged on a single transparent glass plate 90 . The conductive electrodes 97, 98, 99 and 102 to 105 mentioned earlier can advantageously be coatings of opaque metal which are applied to one side of the combined matrix access unit.

The other side of the row access unit, indicated in broken lines in FIG. 6, is shown in detail in FIG. Figure 5 shows a side view of the various supports that make up the tiered access unit of Figures 4 and 6 . The corner pieces of the section shown in Figures 4, 5 and 6 have been cut away so as to fully show the individual elements in a construction plan.

With regard to Fig. 6 , the operation is the same as described above, that the simultaneous impingement of light from an external source on part of the photoconductive element 141 and the momentary opening of the switch 44 lowers the impedance of the element 141 enough to activate the electroluminescent element 142 to excite. The electroluminescent element 142 is arranged to radiate onto the entire photoconductive element 113 and this radiation reduces the impedance of the element so that the voltage source 25 applies a voltage to one side of the crossing point 28 of the matrix. Summarizing the remainder of the description, it can be seen that the electroluminescent element 50 ', partially shown by the dashed lines in the column access unit 40', also glows brightly so that the photoconductive element 114 is also in the low impedance state, and the Voltage source 25 applies an excitation voltage to the intersection 28 of the matrix via the conductive pad 26 .

The dashed outline of the electroluminescent element 142 shows that the photoconductive element 1.45 is arranged in such a way that it receives part of the radiation from the element 142. This small amount of radiation received by element 145 lowers its impedance, and voltage source 52 applies a voltage high enough to electroluminescent element 146 to cause that element to glow darkly. A subsequent brief opening of the switch 44 supplies a voltage high enough to fully excite the electroliminescent element 146. The brightly glowing electroluminescent element 146 emits radiation onto the photoconductive element 143 and lowers the impedance of this element, which is connected in parallel with the electroluminescent element 142 via the transparent, conductive overlay 91 and the conductive electrodes 93 and 98. This state causes the voltage to decrease at the electroluminescent element 142 to such a low value that the element 142 is extinguished.

This way of working results in; that element 146 is in the energized state and element 142 in the de-energized state, which in turn means that photoconductive element 115 has a low impedance while photoconductive element 113 returns to the high impedance state. Thus, the voltage source 25 is switched off from the intersection 28 of the electroluminescent matrix and connected to one side of the intersection 31 via the low impedance of the element 115 . In this way, since the column access unit maintains the photoconductive element 114 in the low impedance state, the voltage source 25 will energize the crossing point 31 .

The process just described is repeated when the switch 44 is briefly opened, so that the third stage with the electroluminescent element 150 is excited and the second stage or the electroluminescent element 146 extinguishes. The photoconductive element 115 is thereby returned to the high impedance state and 25 disconnect the power source from the crossing point 31 of the matrix and create in place of which a 5 voltage from the source 25 via the low impedance of the photoconductive member 117 at the crossing point 34 of the matrix . This process then causes the intersection point 34 of the matrix to glow brightly.

In the operation described above, the radiation from the last electroluminescent element can advantageously be returned to the first photoconductive element , so that the access unit is in a continuous state of excitation and, according to a preselected actuation of the switches 44 and 44 ', any desired pattern on the The screen of the matrix can be generated by the optional excitation of certain crossing points of the matrix.

Claims (2)

PATENT CLAIMS.- 1. Electro-optical device with an electroluminescent matrix, consisting of two intersecting groups of conductors, between whose intersection points electroluininescent material is attached, and with access circles for selecting the intersection points to be excited, characterized in that the conductors (11, 12) each Group of photosensitive elements (13, 15, 17; 14, 16) are connected to an excitation voltage (25) which, however , cannot light up the intersection points (28, 29 ... 39) as long as the photosensitive elements remain unexposed , and that the access circuits contain electroluminescent cells in such a way that each cell is assigned to one of the photoconductive elements in terms of radiation. 2. Apparatus according to claim 1, characterized in that the access circuits are normally held in the de-energized state by photosensitive elements (41) which are connected between the electroluminescent cells (42) and voltage-supplying means (48,52), and that a device ( 56) is provided, which excites a certain photosensitive element (41) of the access circuit. 3. Apparatus according to claim 2, characterized in that the voltage supplying means consist of two series-connected voltage sources (48, 52) which are arranged in such a way that, when one source is short-circuited (44), the particular electrolunescence cell (42 ), which is connected to the photosensitive element (41), glows dark, and that, when the short circuit (44) is canceled, the particular electroluminescent cell (42) glows brightly, and that the particular cell (42) is arranged so that it further energizes the particular photosensitive element (41) to keep the particular cell (42) glowing brightly when the short circuit is restored and to energize (59) the photosensitive element (45) associated with the next successive electroluminescent cell (46 ) the access device is connected to cause this cell (46) to glow dark, and that the removal of the short circuit causes the cell (46) to glow bright, so that the particular electroluminescent cell e (42) stops glowing brightly. 4. Apparatus according to one of the preceding claims, characterized in that the matrix and the access circuits are arranged on a common, transparent, insulating base plate (90) , that the plurality of intersection points of the matrix is represented by a layer of electrolunescent material (101), which is arranged tightly between a first (103, 104) and a second (26) plurality of parallel conductive supports on one side of the base plate, that the photosensitive elements (113, 115) of the matrix, which are also arranged on this side of the base plate, are each connected via electrodes (95, 96) to corresponding conductive pads (104, 103) of the first and second plurality, that the other electrodes (99, 105) of each of these elements are connected to a voltage source (25) , and that the electroluminescent cells (142) of the access devices on the other side of the base plate are arranged so that they light on a corresponding f otosensitive element can transmit. 5. Apparatus according spoke 4, characterized in that the photosensitive elements (41, 45) of the access circles are also arranged on one side of the base plate so that they can transmit light to a corresponding electroluminescent cell (142). Contemplated publications: USA. Patent No. 2,698,915, 2,900,574..