Gaseous-discharge lamp

Abstract: A gaseous-discharge lamp has a tube (2) defining an envelope of the lamp in which an inert gas, such as xenon, is confined. A cup-shaped reflector (10) is disposed in the interior of the lamp, whose inner surface cross-­ section is a hyperbola or an ellipse so that a collimated light spot or parallel light beam is projected outwardly of the lamp. The reflector (10) has a larger-diameter opening facing a light projection window (1) formed on one face of the tube (2) and a bottom portion formed with a hole (9). An anode (6) and a cathode (5) are disposed facing each other in a space surrounded by the reflector (10). A trigger probe electrode (7) is located between the anode (6) and the cathode (5). A sparker electrode (8) is disposed outside the reflector (10) and in the vicinity of the hole (9) formed in its bottom portion. By the provision of the reflector (10) in the interior of the lamp, light of high radiation intensity is produced from the lamp without having to increase its size.

Description: The present invention relates to gaseous-discharge lamps, and more particularly to such a lamp having a reflector in the interior thereof. A conventional gaseous-discharge lamp has an arrangement as shown in Figs. 1 and 2. As shown therein, a glass tube 2 of a circular cross-section serves as an enclosure in which an inert gas is hermetically confined. A light projection window 1 is formed on the top face thereof from which light is projected outwards. A glass stem 3 is provided in the bottom of the tube 2, which includes a circular glass plate 3a and lead wires 4a, 4b, 4c, 4d passing through the glass plate 3a and extending to the interior of the tube 2. Those lead wires are hermetically and fixedly supported by beads 3b. The beads 3b are integrally formed in the glass plate 3a and arranged along a circle in coaxial relation with the circular cross-section of tube 2. In the interior of the tube 2, a cathode 5, an anode 6, a trigger probe electrode 7 and a sparker electrode 8 are disposed which are connected to the lead wires 4a, 4b, 4c and 4d, respectively. The cathode 5 and the anode 6 are oriented in a direction in parallel to the light projection window 1 and are disposed in confrontation with each other with a spacing therebetween. The tip end of the trigger probe electrode 7 is intervened between the cathode 5 and the anode 6. The sparker electrode 8 is disposed at a lower position with respect to the cathode 5, the anode 6, and the trigger probe electrode 7. The sparker electrode 8 is surrounded by a ceramic sleeve so that only the tip end of the electrode 8 projects from it. The outer periphery of the ceramic sleeve is further surrounded by a nickel sleeve 15 which is connected to the cathode lead wire 4a with a lead wire 16. In operation, by the application of a predetermined voltage between the cathode 5 and the anode 6 and first and second trigger voltages to the trigger probe electrode 7 and the sparker electrode 8, respectively, a discharge first occurs between the sparker electrode 8 and the nickel sleeve 15, thereby radiating ultraviolet rays. When the ultraviolet rays are radiated toward the spacing between the cathode 5 and the anode 6, a gaseous arc discharge occurs between the trigger probe electrode 7 and the cathode 5 and then a main discharge occurs between the cathode 5 and the anode 6. Such a lamp has been extensively used as a stroboscopic light source, liquid chromatographic light source, spectrophotometric light source, photo-exciting light source, etc., due to the fact that radiation spectrum covers from ultraviolet to visible or near infrared rays. When the lamp is so used, it is required that a high radiation intensity light be stably emitted from the lamp. However, the conventional lamp per se is incapable of complying with such a requirement. It has therefore been a conventional practice to use a focusing lens or a cup-shaped reflection mirror in conjunction with the lamp for increasing the radiation intensity of the light. The lens is positioned ahead of the light projection window to focus the light projected therefrom. The reflection mirror is attached to the lamp to surround the same so that the light directed backwardly is reflected from the reflection mirror. The use of the lens is inconvenient in that only a particular size of the lens is applicable. The use of the reflection mirror is not so effective due to the presence of a large diameter access hole needed for receiving the lamp. US-4,179,037 and US-4,658,179 disclose gaseous discharge lamp assemblies which are provided with a cup-shaped reflector arranged to project radiation through a light projection window. US-3,840,768 and US-3,775,641 disclose the use of a trigger probe electrode and a sparker electrode to stabilise an electric discharge within a gaseous discharge lamp. According to this invention a gaseous discharge lamp comprises: a tube defining an envelope of the lamp in which a gaseous matter is confined, the tube having a light projection window; an anode supplied with an anode voltage; a cathode confronting the anode with a space between them, a first voltage being applied between the anode and the cathode; a trigger probe electrode assembly having a trigger probe electrode disposed in the space between the anode and cathode, a second voltage lower than the first voltage being applied between the trigger probe electrode and the cathode; and, a sparker electrode, a third voltage being applied between the sparker electrode and the cathode for causing a gaseous discharge to occur between the trigger probe electrode and the cathode, the gaseous discharge further causing a main gaseous arc discharge to occur in a position between the anode and the cathode; the lamp also including a reflector disposed within the tube, the reflector having a cup-shaped configuration with a circular cross-section whose diameter increases towards the light projection window and has a larger diameter opening facing the light projection window and a bottom portion formed with an access hole; wherein, the anode and cathode are surrounded by the reflector; the sparker electrode is disposed outwardly of the reflector in spatial communication with the space through the access hole formed in the bottom portion of the reflector; and, the sparker electrode assembly includes an electric wire connected to said cathode, so that ultraviolet rays are generated by an instantaneous gaseous discharge occurring between the sparker electrode and said electric wire when the trigger voltage is applied to said sparker electrode, the ultraviolet rays being radiated toward the spacing between said anode and said cathode. An advantage of the present invention is that it provides a gaseous-discharge lamp which emits light of a high radiation intensity from compact size gaseous-discharge lamp. The reflector has an inner surface whose cross-section is either a hyperbola or an ellipse, and in the latter case, the anode and the cathode are disposed so that the position where the main gaseous discharge occurs is substantially in coincidence with a focal point of the ellipse. The reflector is made of a metal, preferably aluminum, and is electrically connected to the cathode. By the provision of the reflector, the light of high radiation intensity is projected outwardly of the light projection window. Further, the metal-made reflector is held at the same potential as that of the cathode, the gaseous arc discharge is stabilized in terms of light radiation intensity. The present invention will be better understood from the following description, given by way of example with reference to the accompanying drawings in which: Fig. 1 is a vertical cross-sectional view showing a conventional gaseous-discharge lamp; Fig. 2 is a top plan view showing the conventional gaseous-discharge lamp; Fig. 3 is a vertical cross-sectional view showing a gaseous-discharge lamp according to an embodiment of the present invention; and Fig. 4 is a top plan view showing the gaseous-discharge lamp according to the embodiment of the present invention. The gaseous-discharge lamp of the present invention is electively operable in both a continuous mode and a repetitive pulse mode. When the lamp is operated in the continuous mode, the light of a high radiation intensity is emitted continuously from the lamp whereas when operated as the repetitive pulse mode, flashes of light of a short duration and a high radiation intensity are repetitively emitted therefrom. Referring to Figs. 3 and 4, the internal space of the gaseous-discharge lamp is defined by glass-made enclosure or a tube 2. The tube 2 is of a circular cross-section and has a flat top face serving as a light projection window of which light is projected outwardly and a glass stem 3 provided in the bottom. The glass stem 3 includes a circular glass plate 3a, and at least six lead wires passing through the glass plate 3a. The lead wires are hermetically and fixedly supported by beads 3b integrally formed in the glass plate 3a. A gaseous matter, typically inert gas, such as, xenon, argon, is hermetically confined within the tube. A cathode lead wire 4a passes through the center of the glass plate 3a and extends into the internal space of the lamp. A pair of anode lead wires 4b,4b, a trigger probe lead wire 4c, sparker lead wire 4d and a reflector lead wire 4e also pass therethrough from their respective positions arranged along a circle in coaxial relation with the outer profile of the glass plate 3a. The pair of the anode lead wires 4b, 4b are arranged in radially opposed positions and insulation tubes 11, 11 cover the anode lead wires 4b, 4b. In the interior of the lamp, the anode lead wires 4b, 4b extends upwardly and a plate-like connector 4f bridges between the top ends of the anode lead wires 4b, 4b to electrically connect the same. The connector 4f extends horizontally and the widthwise direction thereof is oriented in the longitudinal direction of the lamp. A lead wire 4g is connected to the mid-portion of the connector 4f to downwardly extend therefrom, and an anode 6 is connected to the lower end of the lead wire 4g. The cathode lead wire 4a extends upwardly into the interior of the lamp and a cathode is connected to the upper end thereof so as to confront the anode 6 with a predetermined spacing therebetween. A trigger probe electrode 7 is disposed in the spacing between the anode 6 and the cathode 5, which electrode 7 is connected to the trigger probe lead wire 4c through a horizontally extending lead wire 4h and a vertically extending lead wire 4i. A cup-shaped reflector 10 made of metal, such as aluminum, is disposed within the lamp to surround the anode 6, the cathode 5, and the trigger probe electrode 7. The reflector 10 has an increasing diameter toward the light projection window 1 and the larger-diameter open end thereof faces the projection window 1. A flange 12 is provided in the upper periphery of the reflector 10 and the anode lead wires 4b, 4b pass therethrough. By the insulation tubes 11, 11, the anode lead wires 4b, 4b and the metal-made reflector 10 are electrically insulated from each other. The reflector lead wire 4e is electrically connected to the flange 12. The reflector 10 is symmetry in its vertical cross-section and the configuration thereof is determined as desired depending upon an intended use thereof. When the lamp is used in conjunction with a focusing lens disposed ahead of the projection window 1, the vertical cross-section thereof is typically configured hyperbolic so that parallel light beam is emitted. When the lamp is used as a light source which produces a focused light as in the case of applying light toward a cross-section of a bundle of optical fibers, it is configured elliptic in vertical cross-section. In this instance, the anode 6, the cathode 5, and the trigger probe electrode 7 are disposed so that the gaseous arc discharge is produced at a focal point of the ellipse. The reflector 10 has a bottom portion formed with an access hole 9 of which the cathode lead wire 4a and the trigger probe lead wire 4i project upwardly. Below the access hole 9, a sparker electrode 8 is disposed which is connected to the sparker lead wire 4d through an extension lead. The sparker electrode 8 is surrounded by a ceramic sleeve 14 so that the tip end of the electrode 8 projects therefrom. The outer periphery of the ceramic sleeve 14 is further surrounded by a nickel sleeve 15 which is connected to the cathode lead wire 4a with a lead wire 16. In operation, when a predetermined voltage is applied between the anode 6 and the cathode 5 and trigger voltages are applied to both the trigger probe electrode 7 and the sparker electrode 8 all at the same timing, a discharge first occurs between the sparker electrode 8 and the nickel sleeve 15, thereby radiating ultraviolet rays. When the ultraviolet rays are radiated toward the spacing between the cathode 5 and the anode 6 through the access hole 9, a gaseous arc discharge occurs between the trigger probe electrode 7 and the cathode 5 and then a main discharge occurs between the cathode 5 and the anode 6, whereby a three-dimensionally diverging light is produced. The rearwardly directing light is reflected rom the reflector 10 and projected outwardly of the light projection window 1 as a whole. Collimating light is given if the reflector 10 is of a hyperbolic configuration in cross-section while focused light is given if the reflector 10 is of an elliptic configuration. When operating the lamp in the repetitive pulse mode, pulsating voltages are applied to the anode 6, the trigger probe electrode 7, and the sparker electrode 8 at the same timing, whereby a flash of light of short duration is projected outwardly of the light projection window 1. On the other hand, when operating the lamp in the continuous mode, a d.c. voltage is applied to the anode 6 and pulsating voltages are applied to the trigger probe electrode 7 and the sparker electrode 8, whereby light is continuously projected outwardly of the light projection window 1. The reflector 10 is connected to the cathode 5 through the lead wire 4e to have the potential of the reflector 10 equal to that of the cathode 5, so that the gaseous arc discharge occurring between the anode 6 and the cathode 5 is stabilized and thus radiation light intensity is maintained substantially constant. As described, the gaseous-discharge lamp according to the present invention incorporates the reflector in the interior of the valve and the sparker electrode is disposed outwardly of the reflector to be in spatial communication with the space where the main arc is taken place. Therefore, the rise-time of the lamp is extremely short when operated in both the continuous and the repetitive pulse modes. More specifically, when the lamp is operated in the continuous mode, the arc discharge occurs immediately after the application of the voltages. When, on the other hand, operated in the repetitive pulse mode, flashes of light of a stable radiation intensity are emitted from the lamp. Further, electromagnetic noises produced attendant to the arc discharge can effectively interrupted by the provision of the reflector, and only the light can be derived from the lamp. In addition, impulse waves produced by the arc discharge are not directly delivered to the valve, the glass stem, and the projection window, damage of the valve can be prevented and the energy loss can be reduced.

Claims: A gaseous-discharge lamp comprising: a tube (2) defining an envelope of the lamp in which a gaseous matter is confined, the tube having a light projection window (1); an anode (6) supplied with an anode voltage; a cathode (5) confronting the anode with a space between them, a first voltage being applied between the anode and the cathode; a trigger probe electrode assembly (7) having a trigger probe electrode disposed in the space between the anode and cathode, a second voltage lower than the first voltage being applied between the trigger probe electrode (7) and the cathode (5) as a first trigger voltage; and, a sparker electrode (8), a third voltage being applied between the sparker electrode (8) and the cathode (5) as a second trigger voltage for causing a gaseous discharge to occur between the trigger probe electrode (7) and the cathode (5), the gaseous discharge further causing a main gaseous arc discharge to occur in a position between the anode and the cathode; the lamp also including a reflector (10) disposed within the tube (2), the reflector having a cup-shaped configuration with a circular cross-section whose diameter increases towards the light projection window (1) and has a larger diameter opening facing the light projection window (1) and a bottom portion formed with an access hole (9); wherein, the anode (6) and cathode (5) are surrounded by the reflector (10); the sparker electrode (8) is disposed outwardly of the reflector (10) in spatial communication with the space through the access hole (9) formed in the bottom portion of the reflector; and, the sparker electrode assembly (8) includes an electric wire (16) connected to said cathode (5), so that ultraviolet rays are generated by an instantaneous gaseous discharge occurring between the sparker electrode (8) and said electric wire (16) when the second trigger voltage is applied between said sparker electrode (8) and said cathode (5), the ultraviolet rays being radiated toward the spacing between said anode and said cathode. A gaseous discharge lamp according to claim 1, wherein the reflector has an inner surface whose cross section is a hyperbola or an ellipse. A gaseous discharge lamp according to claim 2, wherein the anode and the cathode are disposed so that the position where the main gaseous discharge occurs is substantially in coincidence with a focal point of the hyperbola or ellipse. A gaseous discharge lamp according to any one of the preceding claims, wherein the reflector (10) is made of a metal, particularly aluminium. A gaseous discharge lamp according to claim 4, wherein the reflector (10) is electrically connected to the cathode (5). A gaseous discharge lamp according to any one of the preceding claims, wherein the gaseous matter is an inert gas such as xenon or argon. A gaseous discharge lamp according to any one of the preceding claims, wherein the anode, the trigger probe electrode and the cathode are in alignment with one another along a line perpendicular to the light projection window (1). A gaseous discharge lamp according to any one of the preceding claims, wherein the first, second and third voltages are pulsating voltages applied at the same time, whereby flashes of light of short duration are projected outwardly of the light projection window. A gaseous discharge lamp according to any one of the preceding claims, wherein the first voltage is a d.c. voltage and the second and third voltages are pulsating voltages applied at the same time, whereby light is continuously projected outwardly of the light projection window.

Inventors: MIYAMOTO MAKOTO, SHIMAZU YUJI, MIYAMOTO, MAKOTO, SHIMAZU, YUJI, MIYAMOTO, MAKOTO, C/O HAMAMATSU PHOTONICS K.K., SHIMAZU, YUJI, C/O HAMAMATSU PHOTONICS K.K.
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1990
Main classification: H01J61
IPC codes: H01J61