Discharge lamp, image display device using the same and discharge lamp producing method

Abstract: A discharge lamp (1) having a large light output and a stable discharge. On an external surface of a cylindrical glass bulb (2) enclosing a rare gas such as xenon, a pair of beltlike electrodes (5a,5b) are mounted so as to face each other. A light output part (4) is provided between the electrodes, and the electrodes are situated close to each other on the opposite side to the light output part. An image display device is constituted by arranging a plurality of the discharge lamps. A method for producing the discharge lamps is also disclosed.

Description: BACKGROUND OF THE INVENTION i) Field of the Invention: The present invention relates to an image display device according to the pre-characterizing part of each of the claims 1, 3 and 9. ii) Description of the Related Arts: Conventionally, a fluorescent lamp is used as a light source for a copy lighting device of information apparatuses such as a facsimile, a copier, an image reader and the like. For such uses, a small type, a high luminance, a long life and high reliability are required for the lamp. Since the conventional fluorescent lamp is provided with electrodes such as filament electrodes within the tube, the structural limitation imposed by the electrodes is large, and a variety of attempts have been tried for settling problems. In Figs. 23a and 23b, for example, there is shown a conventional fluorescent lamp disclosed in proceedings of 1991 annual conference of the Illumination Engineering Institute of Japan. As shown in Figs. 23a and 23b, the fluorescent lamp 1 comprises a cylindrical glass bulb 2 enclosing rare gases mainly composed of xenon gas therein, a fluorescent substance layer 3 formed on the internal surface of the glass bulb 2, a light output 4 for emitting the generated light in the glass bulb 2 to the outside, a pair of external electrodes 5a and 5b mounted on the external surface of the glass bulb 2 and extending in the longitudinal direction thereof, and a power source 7 for supplying power between the external electrodes 5a and 5b through lead wires 6a and 6b. When a voltage is applied between the external electrodes 5a and 5b from the power source 7, a current flows between them due to the electrostatic capacity therebetween and brings about a discharge between them both. By this discharge, UV (ultraviolet) rays are generated within the glass bulb 2, and the generated UV rays excite the fluorescent substance layer 3 formed on the internal surface of the glass bulb 2 to irradiate visible light outside through the light output part 4. In the conventional fluorescent lamp, the aforementioned various defects due to the presence of the electrodes such as the filament electrodes within the glass bulb 2 can be improved upon. However, the following problems are still present. That is, as shown in Figs. 23a and 23b, the distance between the electrodes on the opposite side to the light output part 4 is almost the same as the width of the light output part 4, and thus the sufficient electrode area can not be taken. Hence, a sufficient light output can not be obtained. Also, as the charged pressure of the rare gases within the glass bulb 2 is increased, the discharge between the electrodes 5a and 5b becomes unstable, and thus a fringe flicker is caused between the electrodes 5a and 5b. Further, since the distance between the electrodes 5a and 5b is wide, the size of the fringe caused between the electrodes 5a and 5b is wide. That is, due to this fringe, the luminance distribution in the longitudinal direction of the fluorescent lamp is uneven. The uneven luminance distribution brings about a problem in a case where the fluorescent lamp is used for the copy lighting of information apparatuses, where a plurality of fluorescent lamps are arranged to constitute an image display device, or the like. US-A-5,013,966 discloses a discharge lamp with external electrodes having a straight glass bulb with a discharge gas charged therein. The electrodes are provided at each longitudinal end portion of the bulb on the outer surface thereof. A high frequency voltage is applied across the electrodes of the discharge lamp. EP-A-0 329 226 describes a low-pressure mercury vapour discharge lamp having a discharge vessel with two parallel rectangular flat glass plates located at a relatively short distance from each other and being transparent to light. The plates are connected in a gas-tight manner by upright walls, and electrodes are arranged in the form of strips on at least two facing upright walls. In JP-A-63-64260 a discharge tube is disclosed having two series of electrodes as coil electrodes arranged along its length on theouter periphery, one series facing the other in readial direction. EP-A-0 348 979 describes a fluorescent lamp having a discharge tube with electrodes sealed one at each end and a phosphor layer on the inner surface. A light transmitting electric insulation layer is provided between the phosphor layer and the inner surface of the tube which can have an elliptical form. In EP-A-0 184 216 a discharge lamp is disclosed which has a plurality of constricting portions axially spaced apart and extending about the circular periphery of the envelope. SUMMARY OF THE INVENTION It is a object of the present invention to provide an image display device using a plurality of discharge lamps arranged, each discharge lamp being capable of obtaining a large light output and a stable discharge and selectively generating a discharge in a plurality of parts. This object is solved by the features of independent claims 1, 3 and 9. Modifications are provided by the subclaims. In the aforementioned image display device with discharge lamps, the electrode area can be widened and thus a large light output can be obtained. By providing the ends of the surface electrodes in close proximity to each other, the discharge generated between the electrodes can be stabilized. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the present invention will more fully appear from the following description of the preferred embodiments with reference to the accompanying drawings, in which: Fig. 1 is a graphical representation showing the relationship between the filled pressure of rare gases in a cylindrical glass bulb and lamp efficiency of the discharge lamp for an image display device according to the present invention; Fig. 2 is a graphical representation showing the relationship between the current density flowing between external electrodes and lamp efficiency of the discharge lamp for an image display device according to the present invention; Fig. 3 is a graphical representation showing the relationship between the frequency of a voltage applied to the external electrodes and luminance of the discharge lamp for an image display device according to the present invention; Fig. 4 is a graphical representation showing the relationship between the distance between the external electrodes and a discharge start voltage of the discharge lamp for an image display device according to the present invention; Figs. 5a and 5b are cross sectional views of a first embodiment of a discharge lamp having a plurality of external electrode pairs arranged in the peripheral direction of a cylindrical glass bulb used for the present invention; Fig. 6 is a schematic perspective view of a second embodiment of a discharge lamp having a plurality of external electrode pairs arranged in the longitudinal direction of a cylindrical glass bulb used for the present invention; Figs. 7a and 7b are perspective views of a third embodiment of a discharge lamp having a plurality of external electrode pairs, in which voltages or currents to be applied to the electrode pairs can be independently controlled, for an image display device according to the present invention; Fig. 8 is a graphical representation showing the relationship between the position from the center of the electrode pair and luminance of the discharge lamp shown in Fig. 7a; Figs. 9a and 9b are schematic perspective and cross sectional views of a fourth embodiment of a discharge lamp having a plurality of external electrode pairs, in which voltages or currents to be applied to the electrode pairs can be independently controlled, for an image display device according to the present invention; Fig. 10 is a schematic perspective view of a first embodiment of an image display device composed of a plurality of discharge lamps shown in Figs. 7a and 7b or Figs. 9a and 9b; Fig. 11 is a schematic perspective view of a second embodiment of an image display device composed of a plurality of three primary colors R, G and B of discharge lamps shown in Figs. 7a and 7b or Figs. 9a and 9b; Fig. 12 is a fragmentary exploded perspective view of a third embodiment of an image display device composed of a plurality of display units each composed of a plurality of discharge lamps shown in Figs. 7a and 7b of Figs. 9a and 9b; Figs. 13a and 13b are schematic elevational and side views of a structure of the electrodes of the display unit shown in Fig. 12 and Figs. 13c and 13d are cross sections, taken along the respective lines 20c - 20c and 20d - 20d in Fig. 13b; Fig. 14 is a perspektive view of a fourth embodiment of an image display device composed of a plurality of discharge lamps held by holding members having a masking function according to the present invention; Fig. 15 is a perspective view of an image display device composed of a plurality of fluorescent lamps held by a holding panel including a plurality of holding members having a masking function according to the present invention; Figs. 16a and 16b are cross sections of another image display device composed of a plurality of discharge lamps held by holding members according to the present invention; Figs. 17a and 17b are cross sectional and elevational views of fifth embodiment of a box type discharge lamp to be used as one pixel for a color image display device, including three primary color (R, G and B) parts according to the present invention; Figs. 18a and 18b and 19a and 19b are schematic perspective and cross sectional views of sixth and seventh embodiments of a discharge lamp having a cylindrical glass bulb with hollowed sections parts on the surface between external electrode pairs for an imgage display device according to the present invention; Fig. 20 is an elevational view showing a method for producing a discharge lamp having a cylindrical glass bulb with hollowed sections on the surface between external electrode pairs for an image display device according to the present invention; Fig. 21 is an elevational view showing another method for producing a discharge lamp having a cylindrical glass bulb with hollowed sections on the surface between external electrode pairs for an image display device according to the present invention; Fig. 22 is a cross sectional view of an eighth embodiment of a discharge lamp having electrodes formed on the internal surface of a container, the inside of the electrodes being covered by a dielectric layer, for an image display device according to the present invention; and Figs. 23a and 23b are a partially cut away and a cross sectional view respectively, of a conventional fluorescent lamp. DESCRIPTION OF THE PREFERRED EMBODIMENTS It is now referred to the drawings, wherein like reference characters designate like or corresponding parts throughout the views and thus the repeated description thereof can be omitted for brevity. In Fig. 1 there is shown the relationship between an enclosed rare gas pressure within a cylindrical glass bulb and lamp efficiency of a fluorescent lamp used in an image display device according to the present invention. The lamp efficiency can be obtained from a value calculated by dividing the luminance by the electric power. It is readily understood from Fig. 1 that, as the enclosed lgas pressure is decreased, the lamp to be due to the fact efficiency is suddenly reduced. This is considered that, since the light generation is due to the UV rays generated by an excimer and the generation of the excimer is due to the collision between the rare gas atoms, a low enclosed rare gas pressure brings about a low probability of the excimer formation. The fine filiform discharge can be observed at a pressure of more than 399 Pa (30 Torr). At a lower pressure than 399 Pa (30 Torr), the discharge is extended like a glow discharge, and the radiation of near IR (infrared) rays of the atomic spectrum of the rare gas becomes strong. From the viewpoint of the effective generation of the excimer and the use of its light generation, the enclosed gas pressure is preferably more than 399 Pa (30 Torr). In Fig. 2, there is shown the relationship between density of a current flowing between the external electrodes and the lamp efficiency of the fluorescent lamp. Since the discharge is generated at only the portions facing the external electrodes, the characteristics of the lamp can be largely affected by the current density rather than the whole amount of current flowing in the lamp. That is, since the electrode area is large, the large electric power can be committed to the medium for the discharge even at the low current density and hence the efficiency is high. Further, when the current density is low, the intensity of the near IR in infrared rays irradiated by the xenon atom is weak. In the lamp including the electrodes therein, since the current density near the electrodes is high, the near IR rays as the atomic spectrum of the rare gas are strong, which is detrimental to the copy reading in the facsimile. Hence, it is necessary to use a filter for cutting the near IR rays. In the present fluorescent lamp, no such filter is required and it is quite suitable for copy reading in the facsimile or the like. In Fig. 3, there is shown the relationship between the frequency of the voltage applied to the external electrodes and the luminance of the fluorescent lamp. It is readily understood from Fig. 3 that the higher the frequency, the higher the luminance obtained. The reason for this is as follows. That is, since the voltage is applied from the external surface of the glass, as the frequency is lowered, the impedance of the glass increases, and it is difficult to supply sufficient electric power to the rare gas. Further, when the frequency is low, the discharge is apt to be unstable, and uneven luminance is liable to be caused. Also, since the noise is inclined to be caused when a relatively high voltage is used, the harsh noise is apt to be generated in the audio frequency band. From the view points described above, in this embodiment, the lamp is preferably supplied with a voltage a frequency of more than 20 kHz. On the other hand, since, as the frequency is increased, the larger electric power can be supplied and the luminance becomes higher, the current density is increased and thus the efficiency drops. Further, by providing the electrodes outside of the bulb, it is hard to avoid the generation of a magnetic noise, and in order to avoid interference to a radio receiver or the like, the frequency of the voltage is preferably less than 500 kHz lower than the radio frequency. In Fig. 4, there is shown a discharge start voltage when an interval between the external electrodes is varied at an enclosed gas pressure of 399 Pa (30 Torr) in the fluorescent lamp 1. It is apparent from Fig. 4 that the discharge start voltage is increased almost in proportion to the interval between the electrodes. That is, it is considered that the discharge system of this fluorescent lamp meets Paschen's law, that is, as the enclosed gas pressure is increased, the discharge start voltage is raised. Hence, the interval between the electrodes is preferably as narrow as possible, but, in practice, it is preferably less than 3 mm. In the lamp of this embodiment, even when the inverval between the electrodes is narrow, the efficiency is not reduced, and as a result, the discharge start voltage can be reduced, unlike a conventional fluorescent lamp using a light generation of a positive column generated at a separate position from the electrodes. Further, since the UV rays are mainly generated on the internal surface of the lamp facing the electrodes, when the electrode area is large, the light output is large. In particular, when the opening angle of the light output part is large and the external electrodes are positioned on the opposite side to the light output part, it is very much effective to obtain the large light output. Furthermore, since the discharge is stable, attributable to the narrow distance between the electrodes, the uniform luminance distribution can be obtained in the axial or longitudinal direction of the cylindrical container such as the glass bulb. In addition, since, as the electrode interval is narrowed, the interval of the fringy discharge is narrowed, by observing the discharge state, it is found that the luminance distribution is further made uniform. In Figs. 5a and 5b, there is shown the first embodiment of a discharge lamp used for an image display device according to the present invention. In this embodiment, at least two pairs of external electrodes 5a and 5b are formed on the external surface of the glass bulb 2 in the peripheral direction thereof, as shown in Fig. 5a, or two electrodes 5a are formed on both sides of the electrode 5b in the peripheral direction of the glass bulb 2, as shown in Fig. 5b. In this case, the discharge is caused between each pair of electrodes. In the first embodiments, as described above, although the external electrodes 5a and 5b are formed over the entire external surface of the glass bulb 2 except the light output part 4, when not so large a light output is required, the electrodes 5a and 5b can be formed on only part of the external surface of the glass bulb 2. In Fig. 6, there is shown the second embodiment of the discharge lamp for an image display device according to the present invention. In this embodiment, a plurality of electrode pairs are arranged on the external surface of the glass bulb 2 in the longitudinal direction thereof. In this case, even in a long lamp, the UV rays generation amount becomes uniform at any part in the longitudinal direction, and an improved luminance distribution over the entire length of the lamp can be obtained. In the fluorescent lamp 1 shown in Figs. 5a and 5b, of course, a plurality of electrode pairs can be arranged in the longitudinal direction of the glass bulb 2 in the same manner as described above. In Figs. 7a and 7b, there is shown the third embodiment of the discharge lamp for an image display device according to the present invention. In this embodiment, a plurality of external electrode pairs are arranged in the longitudinal direction of the cylindrical glass bulb 2, and an electric power source 7 for applying a voltage or current and a switching element connected in series with the electric power source 7 are provided for each electrode pair so as to independently control the voltages or currents applied to the electrode pairs. By carrying out an ON - OFF control of each switching element, only electrode parts with a voltage applied start to perform the discharge to emit the light. This utilizes the phenomenon that the discharge is generated at only the electrode parts with a voltage applied and is not extended outside therefrom. For instance, in the fluorescent lamp 1 shown in Fig. 7a, with the cylindrical glass bulb 2 diameter of 10 mm and a light output part 4 opening angle of 180 0t, the fluorescent substance layer 3 is formed on the half of the peripheral surface of the glass bulb 2, and a plurality of electrode pairs, each being composed of two electrodes having a width of approximately 12 mm and arranged a distance of approximately 1 mm apart, are arranged at a pitch of 36 mm. Now, when the voltage is applied to only one electrode pair to cause it to discharge, the luminance distribution measured in the longitudinal direction of the lamp is as shown in Fig. 8 wherein the center of the electrode pair is determined to be at0 mm on the positional scale. In this case, when the discharge is generated between the electrode pair, the surface of the electrode parts are brightly illuminated, and at the 0 mm position having no electrode, the luminance is somewhat reduced. As described abvove, only the electrode parts with the voltage applied can be illuminated, and a considerably high luminance ratio of the illuminated part with reference to the adjacent unilluminated part can be obtained. That is, in the system of this embodiment, the light generation of parts of the glass bulb 2 can be controlled without providing a plurality of electrodes within the glass bulb 2. Accordingly, the fabrication of this lamp can be extremely easily carried out, and the influence of the unevenness of the electrode characteristics is small compared with a light generation control of the conventional lamp including a plurality of electrodes within the lamp. Hence, the reliability of the fluorescent lamp for an image display device according to the present invention is extremely high. In Figs. 9a and 9b, there is shown teh fourth embodiment of the discharge lamp for an image display device according to the present invention. In this embodiment, a plurality of external electrode pairs are formed on approximately half the external peripheral surface of the cylindrical glass bulb 2 and are arranged in the longitudinal direction of the glass bulb 2, and the fluorescent substance layer 3 is formed on approximately half the internal peripheral surface facing the electrodes. The plurality of electrode pairs are connected to one electric power source 7 through the respective switching elements. In the fluorescent lamp having the above-described construction, the projection area of the light output part 4 can be made maximum. This means that the rate of the lighting area against the image display area can be made large when this fluorescent lamp is applied to an image display device hereinafter described in detail, and a high quality display device can be obtained. In Fig. 10, there is shown the first embodiment of an image display device according to the present invention produced by arranging a plurality of fluorescent lamps 1 shown in Figs. 7a and 7b or Figs. 9a and 9b. In this embodiment, one electrode pair is used as one pixel, and a voltage is selectively applied to a plurality of electrode pairs arranged to display a symbol, a character, a figure or the like. In Fig. 9, there is shown the second embodiment of an image display device 10 according to the present invention produced by arranging a plurality of fluorescent lamps shown in Figs. 7a and 7b or Figs. 9a and 9b. In this embodiment, the fluorescent lamps are divided into fluorescent lamps 1a, 1b and 1c of three primary colors R, G and B to constitute a full color image display device 10. The fluorescent lamps 1a, 1b and 1c of three primary colors R, G and B can be obtained by changing the illumination color of the fluorescent substance formed on the internal surface of the glass bulb 2 of the fluorescent lamp. In this case, by using three such color fluorescent lamps, a inexpensive color image display device having an extremely high reliability can be easily produced. Further, in this embodiment, the fluorescent lamp utilizing th UV rays irradiated by the excimer has high efficiency compared with a conventional fluorescent lamp using the UV rays irradiated by an atom. In a conventional fluorescent lamp using the discharge between internal electrodes for use in a display device, for example, as disclosed in Japanese Patent Laid-Open No. Hei 2-129847 and Japanese Utility Model Laid-Open No. Sho 61-127562, since the IV rays irradiated from the positive column generated between the electrodes is utilized, when the electrode distance is narrow, the efficiency is bad. However, in the present fluorescent lamp, since the narrower electrode distance brings about better efficiency, the pixel size can be reduced without reducing the efficiency. Further, in the conventional fluorescent lamp, since a filament hot cathode is used, heat is largely generated by the preheating of the filament and thus the efficiency is low. In turn, in the image display device according to the present invention, since the efficiency is high and the heat generation is low, a large scale cooling device used in the conventional image display device is not required. Further, in the conventional fluorescent lamp, since mercury is used, there is temperature dependency, and in the conventional image display device, a temperature control device for maintaining the temperature of the lamp is required. In turn, in the present fluorescent lamp, since only the rare gas is used, there is no temperature dependency, and the temperature control device is not required. In Fig. 12, there is shown the third embodiment of an image display device 10 composed of a plurality of display units 11 according to the present invention each composed of a plurality of discharge lamps 1 shown in Figs. 7a and 7b or Figs. 9a and 9b. In this embodiment, each display unit 11 is formed with feeding pins 12 connected to external terminals 5 of the fluorescent lamps 1, and the feeding pins 12 of the display unit 11 are connected to feeding terminals 13 provided on a body 14 of the image display device 10 to thus mount the display unit 11 to the body 14. As described above, an image plane of the image display device 10 is divided into a plurality of subimage planes composed of the display units 11. This construction is very effective for producing a large scale display device having a large image plane. That ist, in the large scale display device, if the system can not be unitized, it is necessary to fabricate fluorescent lamps having a long length depending on the size of the image plane. However, in this embodiment, by using the unitized fluorescent lamps, the display device having a large image plane can be readily constructed by increasing the number of the display units 11. Hence, the assembling of the image display device can be readily carried out, and the breakage of the lamps can be effectively prevented. In Figs. 13a to 13d, there is shown a construction of the electrodes of the display unit shown in Fig. 12. In this instance, as shown in Fig. 13a, the structure has a similar structure to the matrix wiring used for a liquid crystal image display device. The display unit 11 is comprised of a matrix of 6 x n pixels 11-11, 11-21 ....., 11-n6, and as shown in Figs. 13b to 13d, for the matrix of the columns and the rows of the pixels, one set of external electrodes 5a corresponding to the columns are connected to feeding pins X1 to X6 and the other set of external electrodes 5b corresponding to the rows are connected to Y feeding pins Y1 to Yn. In this matrix type display unit 11, in order to illuminate the pixel 11-32, the switching elements (not shown) connected to the feeding pins X2 and Y3 are turned on to apply the voltage to the electrode pair corresponding to the pixel 11-32. In the structure of the display unit 11 as described above, the number of the feeding pins compared with the number of the pixels can be largely reduced. In this embodiment, although 2 sets of the fluorescent lamps of the three primary colors R, G and B, that is, 6 fluorescent lamps altogether are unitized for each row of the display unit 11, the number of the fluorescent lamps is not restricted to this number, and any number of the fluorescent lamps can be used so long as they are in groups of three for the three primary colors R, G and B in one unit. In the aforementioned image display devices according to the present invention using the cylindrical discharge lamps, as shown in Fig. 8, there occurs a little light generation between the adjacent electrode pairs, and due to this light generation, the contrast of the image is sometimes deteriorated. In order to improve this problem, a mask for covering the space between the electrode pairs can be provided. A holding member for holding the fluorescent lamps 1 can be used as a mask as well. Some embodiments of this case are shown in Figs. 14, 15, 16a and 16b. In Fig. 14, there is shown the fourth embodiment of an image display device according to the present invention composed of a plurality of fluorescent lamps held by holding members 20 having a masking function. In this embodiment, the holding members 20 also mask the space between the electrode pairs. In Fig. 15, there is shown an image display device 11 according to the present invention composed of a plurality of fluorescent lamps 1 held by a holding panel 21 including a plurality of holding members 20 having a masking function. In this embodiment, a plurality of holding members 20 are constructed to the holding panel 21 every display unit 11. In Figs. 16a and 16b, there is shown another image display device according to the present invention composed of a plurality of fluorescent lamps 1 held by holding members 22 and 23. As shown in Fig. 16a, the fluorescent lamps 1 are held to the display unit 11 by the holding member 22 of an epoxy resin or the like. As shown in Fig. 16b, the fluorescent lamps 1 are held to the display unit 11 by the holding member 23 of a transparent resin material or the like so that the transparent resin holding member 23 may completely cover the fluorescent lamps 1. In this embodiment, the holding of the fluorescent lamps 1 to the display unit 11 can be exactly performed, and further the dielectric breakdown between the electrodes can be prevented by the resin material. Further, the fluorescent lamps 1 are entirely covered by the transparent resin material to improve the waterproof property, as shown in Fig. 16b. In Figs. 17a and 17b, there is shown the fifth embodiment of a box type fluorescent lamp 30 to be used as one pixel for a color image display device according to the present invention. In this embodiment, the fluorescent lamp 30 includes three primary color illumination parts 31, 32 and 33 of red R, green G and blue B. A plurality of fluorescent lamps 30 as the pixels are arranged in a matrix form on a flat surface to constitute a color image display device. In the fluorescent lamp shown in Figs. 7a and 7b or Figs. 9a and 9b, the discharge is generated between each electrode pair, but the generated light is projected to the outside. When these fluorescent lamps are used for the display device, the outline of the pixel becomes dim. Further, the discharge can be generated between the adjacent electrode pairs. In order to improve these problems, other embodiments of the fluorescent lamps are developed as shown in Figs. 18a and 18b and Figs. 19a and 19b. In Figs. 18a and 18b, there is shown the sixth embodiment of a fluorescent lamp 1 for an image display device according to the present invention. In this embodiment, hollow portions 2a are formed on the peripheral surface of the cylindrical glass bulb 2 between the electrodes constituting the electrode pairs of the fluorescent lamp shown in Fig. 7b. In this case, by providing the hollow portions 2a on the glass bulb 2 between the electrode pairs, the mixing of the light generated at the adjacent electrode pairs can be largely reduced. By using this fluorescent lamp in the display device, an image display device having a simple construction can be produced, and a clear outline display can be performed. In Figs. 19a and 19b, there is shown the seventh embodiment of a fluorescent lamp 1 for an image display device according to the present invention. In this embodiment, hollow portions 2a are formed on the peripheral surface of the cylindrical glass bulb 2 between the electrodes constituting the electrode pairs of the fluorescent lamp shown in Fig. 9a. The same effects as those of the sixth embodiment shown in Figs. 18a and 18b can be obtained. In Fig. 20, there is shown one method for producing a discharge lamp having the hollow portions 2a on the peripheral surface of the cylindrical glass bulb 2 between the external electrode pairs for an image display device according to the present invention. In this embodiment, before one open end of the glass bulb 2 is closed, the glass bulb 2 is heated at the positions where the hollow portions 2a by are to be formed a heating device 40. During the heating of the glass bulb 2, the gas enclosed in the glass bulb 2 is sucked from the open end of the glass bulb 2, by using an exhaust system (not shown) such as a vacuum pump, to reduce the pressure in the glass bulb 2. Then, the portions which have become softened by the heating become depressed by virtue of the reduced pressure in the glass bulb 2 to thus form the hollow portions 2a on the glass bulb 2 of the fluorescent lamp shown in Figs. 18a and 18b or Figs. 19a and 19b. In Fig. 21, there is shown another method for producing a discharge lamp having the hollow parts 2a on the peripheral surface of the cylindrical glass bulb 2 between the external electrode pairs for an image display device according to the present invention. In this embodiment, the inside of the glass bulb 2 is sucked to reduce the pressure inside thereof in advance, and, after the discharge medium such as the rare gas is enclosed in the reduced glass bulb 2 so that the pressure in the glass bulb 2 ist still lower than the atmospheric pressure, the glass bulb 2 is heated at positions where the hollow portions 2a are to be formed by the heating device 40. During the heating of the glass bulb 2, the portions which have become softened by the heating become hollow due to the difference between the inside pressure of the glass bulb 2 and the atmospheric pressure to thus form the hollow portions 2a on the glass bulb 2 of the fluorescent lamp shown in Figs. 18a and 18b or Figs. 19a and 19b. In the above-described embodiments, although the surface electrodes are formed by the sheet form electrodes, net form electrodes or electrodes formed by arranging a plurality of linear materials in parallel can also be used. Further, although a plurality of electrodes are arranged in the axial direction or perpendicular direction of the cylindrical container or the like, the electrodes can be arranged in an inclined direction of the container. Also, although the electrodes are mounted on the external surface of the glass bulb 2 and the discharge is generated between the electrodes via the glass of the dielectric substance, the electrodes can be embedded in the dielectric substance. In Fig. 22, there is shown the eighth embodiment of a fluorescent lamp having electrodes formed on the internal surface of a box type container, the inside of the electrodes being covered by a dielectric layer, for an image display device according to the present invention. In this embodiment, the electrodes 5a and 5b are formed on the internal surface of a container body 9, and then the dielectric substance is formed on the internal surface side of the electrodes so as to cover the same by a vapor deposition or the like to form a dielectric substance layer 50. A fluorescent substance layer 3 is formed on the dielectric substance layer 50 opposite to a light output part 4. The light output part 4 is formed of a glass material, but the material of the container body 9 is not restricted to glass material. In this embodiment, the container body 9 is formed of a ceramic material. In this instance, the dielectric substance layer 50 is not subjected to a stress caused by the pressure difference between the inside and the outside of the fluorescent lamp, and thus it can be made thinner compared with the above-described embodiments. As a result, the field intensity of the discharge space can be enlarged, and the impedance of the dielectric substance layer 50 can be reduced. Hence, the discharge of the fluorescent lamp can be carried out at a low voltage. In the aforementioned embodiments, although xenon is used as the rare gas enclosed within the lamp, another rare gas such as krypton, argon, neon or helium, a mixture of at least two rare gases or another medium for discharging can be used. Further, although the present invention is applied to the fluorescent lamp, the UV rays generated by the discharge are not necessarily converted into visible light and can be utilized as a UV lamp. As described above, the following effects can be obtained. (1) Since the area of the surface electrodes can be widened compared with the conventional lamp, a large light output can be obtained. (2) Since the edges of the surface electrodes are made close to one another, the discharge becomes stable. (3) Since the discharge is generated at only the electrode parts to which the voltage is applied, a plurality of electrode pairs are mounted on one fluorescent lamp, and by selectively applying the voltage to the electrode pairs, a plurality of parts divided in one fluorescent lamp can be selectively illuminated. Hence, when this fluorescent lamp is used for illumintion, the number of the electrode pairs that the voltage is applied to is varied to change the luminance, illumination positions and the like. Further, a plurality of fluorescent lamps are arranged to constitute an image display device. Further, by providing the fluorescent lamps of three primary colors such as red, green and blue, a color image display device can be produced. (4) In the case of the fluorescent lamp in which a plurality of divided parts are selectively illuminated, by providing hollow portions between the electrode pairs, the discharge between the adjacent two electrode pairs can be prevented, and the leakage of light from the electrode pair illuminating to the outside can also be prevented. (5) By using the method for producing the fluorescent lamp having hollow portions, the fluorescent lamp can be easily produced. Although the present invention has been described in its preferred embodiments with reference to the accompanying drawings, it is readily understood that the present invention is not restricted to the preferred embodiments and that various changes and modifications can be made by those skilled in the art without departing from the scope of the claims.

Claims: An image display device (10), comprising: a plurality of discharge lamps (1) arranged in parallel, each of said discharge lamps (1) comprising a container (2) for enclosing a medium for discharge therein; electrode means (5a,5b) to which a predetermined voltage is to be applied for exciting discharge space within said container (2), characterized in that said electrode means (5a, 5b) have a plurality of surface electrode pairs (5a, 5b) for receiving the predetermined voltage to excite the discharge space within the container (2), each electrode pair being disposed with a dielectric placed between the electrode pair and a gas; such that visible light is created at an inner surface of the container (2) substantially opposing the electrode means (5a, 5b); each surface electrode having two ends and a relative distance between one pair of ends facing each other being shorter than a relative distance between the other pair of ends facing each other; and means for controlling the predetermined voltage such that the predetermined voltage is selectively applied to the surface electrode pairs (5a, 5b). The image display device of claim 1, wherein the container (2) of said discharge lamp (1) is cylindrical, and the surface electrode pair (5a, 5b) is mounted on a peripheral surface of said cylindrical container (2) on opposite sides of said discharge space. An image display device (10), comprising: a plurality of discharge lamps (1) arranged in parallel, each of said discharge lamps (1) comprising a container (2) for enclosing a medium for discharge therein; electrode means (5a,5b) to which a predetermined voltage is to be applied for exciting discharge space within said container (2), characterized in that said electrode means (5a, 5b) have a plurality of surface electrode pairs (5a, 5b) for receiving the predetermined voltage to excite the discharge space within the container (2), each electrode pair being disposed with a dielectric placed between the electrode pair and a gas; such that visible light is created at an inner surface of the container (2) substantially opposing the electrode means (5a, 5b); each surface electrode pair (5a, 5b) being arranged to be coaxially adjacent to each other in a longitudinal direction of said container (2); and means for controlling the predetermined voltage such that the predetermined voltage is selectively applied to the surface electrode pairs (5a, 5b). The image display device of claim 2 or 3, wherein the plurality of discharge lamps (1) include discharge lamps (1a, 1b, 1c) which generate red, green and blue color light. The image display device of claim 4, wherein predetermined sets of red, green and blue color discharge lamps (1a, 1b, 1c) constitute a unit (11), and a plurality of said units are arranged in a matrix form. The image display device of one of claims 1 to 5, further comprising a holder (20, 21) for holding said discharge lamps (1) from a first side, the holder (20, 21) arranged in a direction perpendicular to a longitudinal direction of said discharge lamps (1), said holder (20, 21) covering the space between said electrode pairs (5a, 5b) of said discharge lamps (1). The image display device of one of claims 1 to 5, further comprising a holder (14) for holding said cylindrical discharge lamps (1) from a second side, said holder (14) being formed along the second side of said discharge lamps (1). The image display device of one of claims 1 to 5, further comprising a holder (23) of transparent resin material for embedding and holding said discharge lamps (1). An image display device (10), comprising: a plurality of discharge lamps (1) arranged in parallel, each of said discharge lamps (1) comprising a container (2) for enclosing a medium for discharge therein; electrode means (5a,5b) to which a predetermined voltage is to be applied for exciting discharge space within said container (2), characterized in that said electrode means (5a, 5b) have a plurality of surface electrode pairs (5a, 5b) for receiving the predetermined voltage to excite the discharge space within the container (2), each electrode pair being disposed with a dielectric placed between the electrode pair and a gas; such that visible light is created at an inner surface of the container (2) substantially opposing the electrode means (5a, 5b); the form of the container of said discharge lamp (30) being a box, and the surface electrode pairs (5a, 5b) are mounted on one surface of said box container of said discharge space; the edges of the surface electrodes being close to one another, and means for controlling the predetermined voltage such that the predetermined voltage is selectively applied to the surface electrode pairs (5a, 5b). The image display device of claim 9, wherein each said discharge lamp (30) includes red, green and blue color light generation parts (31, 32, 33). The image display device of claims 1 to 10, wherein a rare gas is enclosed in the container (2) of said discharge lamps (1), and an exciter of the rare gas is generated by the discharge between said electrodes (5a, 5b). The image display device of claim 11, wherein said rare gas is xenon.

Inventors: HOSHIZAKI JUNICHIRO, MATSUMOTO SADAYUKI, MYODO OSAMU, NISHIMATSU HISAE, SAIKATSU TAKEO, SAKURAI TAKEHIKO, SAWADA HARUMI, YAMADA TOSHIO, YOSHIOKA KAZUO, HOSHIZAKI, JUNICHIRO, MATSUMOTO, SADAYUKI, MYODO, OSAMU, NISHIMATSU, HISAE, SAIKATSU, TAKEO, SAKURAI, TAKEHIKO, SAWADA, HARUMI, YAMADA, TOSHIO, YOSHIOKA, KAZUO, HOSHIZAKI, JUNICHIRO, C/O MITSUBISHI DENKI K.K., MATSUMOTO, SADAYUKI, C/O MITSUBISHI DENKI K.K., Myodo, Osamu, c/o Mitsubishi Denki K.K., Nishimatsu, Hisae, c/o Mitsubishi Denki K.K., SAIKATSU, TAKEO, C/O MITSUBISHI DENKI K.K., SAKURAI, TAKEHIKO, C/O MITSUBISHI DENKI K.K., Sawada, Harumi, c/o Mitsubishi Denki K.K., Yamada, Toshio, c/o Mitsubishi Denki K.K., YOSHIOKA, KAZUO, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: H01J65
IPC codes: H01J65, H01J61, G09F9, H01J9, G09G3