Patent Publication Number: US-9431233-B2

Title: Plasma lighting system with a metallic material in the bulb

Description:
This application claims the benefit of Korean Patent Application No. 10-2014-0004380, filed on Jan. 14, 2014, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma lighting system and more particularly, to a plasma lighting system which may reduce the time it takes to turn the light back on (a light-on condition) after the light is turned off (a light-off condition). 
     2. Discussion of the Related Art 
     In general, a lighting system using microwaves (several hundred MHz to several GHz) is designed to generate visible light by applying microwaves to an electrodeless plasma bulb. 
     The microwave lighting system is an electrodeless discharge lamp in which a quartz bulb having no electrode is filled with inert gas. 
     Recently, the microwave lighting system is configured to emit a continuous spectrum in a visible light range via high voltage electric discharge of sulfur. The microwave lighting system is also referred to as a plasma lighting system. 
     In the plasma lighting system, the interior of the bulb remains in a high pressure state immediately after a light-off condition. Accordingly, electric discharge does not occur and a light-on condition cannot be implemented again until the internal pressure of the bulb falls below a given level via cooling after a light-off condition. 
     That is, much time is needed until a light-on condition can be obtained immediately after a light-off condition, which makes it difficult to instantly cope with an unexpected situation, etc. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a plasma lighting system that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     One object of the present invention is to provide a plasma lighting system which may reduce time taken until a light-on condition can be achieved after a light-off condition. 
     Another object of the present invention is to provide a plasma lighting system which may cause electric discharge even in a state in which the interior of a bulb remains in a high pressure state, thereby enabling a relatively instantaneous light-on condition. 
     Another object of the present invention is to provide a plasma lighting system which may allow an electric field in the interior of a bulb to be concentrated on a metallic material, thereby achieving an electric field intensity required for electric discharge. 
     A further object of the present invention is to provide a plasma lighting system which may achieve a luminous flux of a given level or more and maintain a desired luminous efficacy. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a plasma lighting system includes a magnetron configured to generate microwaves, and a bulb in which a dose for generation of light under the influence of the microwaves and at least one metallic material for generation of thermal electrons are received. 
     The metallic material may include at least one selected from the group consisting of tungsten (W), tantalum (Ta), molybdenum (Mo), rhenium (Re), lanthanum hexaboride (LaB 6 ) and cerium hexaboride (CeB 6 ). 
     The metallic material may be surrounded by an insulation capsule. 
     The insulation capsule may be formed of quartz or ceramic. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  is a conceptual view showing a plasma lighting system according to one embodiment of the present invention; 
         FIG. 2  is an exploded perspective view showing the plasma lighting system according to the embodiment of the present invention; 
         FIG. 3  is a conceptual view showing a constituent metallic material of the plasma lighting system according to one embodiment of the present invention; and 
         FIGS. 4 and 5  show simulation results explaining effects of the plasma lighting system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a plasma lighting system according to one embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     The accompanying drawings show an exemplary configuration of the present invention and are merely provided to describe the present invention in detail, and the scope of the present invention is not limited by the accompanying drawings and the detailed description thereof. 
       FIG. 1  is a conceptual view showing a plasma lighting system according to one embodiment of the present invention, and  FIG. 2  is an exploded perspective view showing the plasma lighting system according to the embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , the plasma lighting system, designated by reference numeral  100 , includes a magnetron  110 , a waveguide  120  and a bulb  140 . In addition, the plasma lighting system  100  may include a resonator  130  surrounding the bulb  140  and a drive unit  170  (e.g., a motor) to rotate the bulb  140 . 
     In addition, the plasma lighting system  100  may include a housing  180  defining an external appearance of the plasma lighting system  100 . The drive unit  170  and/or the magnetron  110  may be received in the housing  180 . 
     Hereinafter, the respective constituent elements of the plasma lighting system  100  will be described in detail. 
     The magnetron  110  serves to generate microwaves having a predetermined frequency. In addition, a high voltage generator may be formed integrally with or separately from the magnetron  110 . 
     The high voltage generator generates a high voltage. As the high voltage generated by the high voltage generator is applied to the magnetron  110 , the magnetron  110  generates microwaves having a radio frequency. 
     The waveguide  120  includes a waveguide space  121  for guidance of the microwaves generated by the magnetron  110 , and an opening  122  for transmission of the microwaves to the resonator  130 . 
     An antenna unit  111  of the magnetron  110  may be inserted into the waveguide space  121 . The microwaves are guided through the waveguide space  121 , and thereafter transmitted to the interior of the resonator  130  through the opening  122 . 
     The resonator  130  creates a resonance mode by preventing outward discharge of the introduced microwaves. The resonator  130  defines a resonance space. The resonator  130  may function to generate a strong electric field by exciting the microwaves. 
     In one embodiment, the resonator  130  may have a mesh form. 
     In addition, to allow the microwaves to be introduced into the resonator  130  only through the opening  122 , the resonator  130  may be mounted to surround the opening  122  of the waveguide  120  and the bulb  140 . 
     A reflective member  150  may be mounted at the opening  122  of the waveguide  120  to surround a portion of the opening  122 . 
     More specifically, the reflective member  150  may be mounted at a predetermined region  123  of the waveguide  120  having the opening  122 . The bulb  140  may penetrate the predetermined region  123  to thereby be connected to the motor  170 . The predetermined region  123  may be surrounded by the resonator  130 . The predetermined region  123  has an insertion hole  124  for insertion of the rotating shaft  142  of the bulb  140 . 
     Meanwhile, the reflective member  150  functions to guide the microwaves to be introduced into the resonator  130  through the opening  122 . 
     In addition, the reflective member  150  may function to reflect the microwaves introduced into the resonator  130  toward the bulb  140 , in order to concentrate an electric field on the bulb  140 . 
     The bulb  140 , in which a light emitting material is received, may be placed within the resonator  130 , and a rotating shaft  142  of the bulb  140  may be coupled to the motor  170  as described above. 
     Rotating the bulb  140  via the motor  170  may prevent generation of a hot spot or concentration of an electric field on a specific region of the bulb  140 . 
     The bulb  140  may include a spherical casing  141  in which a light emitting material is received, and the rotating shaft  142  extends from the casing  141 . 
     In addition, a photo sensor  143  may be mounted to the rotating shaft  142 . The photo sensor  143  functions to sense optical properties of light emitted from the bulb  140 . More specifically, the photo sensor  143  may serve to sense optical properties of light having passed through a clearance between the rotating shaft  142  of the bulb  140  and the insertion hole  124 . 
     The magnetron  110  is controlled by a controller  190 . More specifically, the controller  190  may control ON/OFF and output power of the magnetron  110 . In addition, the controller  190  may control ON/OFF and Revolutions Per Minute (RPM) of the motor  170 . In addition, the controller  190  may be placed in the housing  180 . 
     The light emission principle of the plasma lighting system  100  having the above-described configuration will be described below. 
     Microwaves generated in the magnetron  110  are transmitted to the resonator  130  through the waveguide  120 . 
     Then, as the microwaves introduced into the resonator  130  are resonated in the resonator  130 , the light emitting material in the bulb  140  is excited. 
     In this case, the light emitting material received in the bulb  140  generates light via conversion thereof into plasma, and the light is emitted outward of the resonator  130 . 
     Meanwhile, the plasma lighting system  100  may further include a reflective member (not shown) to adjust the direction of light emitted from the bulb  140  and to guide the light outward of the resonator  130 . The reflective member may be a semi-spherical shade. 
       FIG. 3  is a conceptual view showing a constituent metallic material of the plasma lighting system according to one embodiment of the present invention. 
     The bulb  140  receives a dose for generation of light under the influence of microwaves and at least one metallic material  210  for discharge (generation) of thermal electrons. In addition, the bulb  140  is filled with an inert gas such as argon (Ar). 
     In this specification, the term “dose” represents a light emitting material that emits light by being excited by microwaves. The dose and the metallic material  210  are received in the casing  141  of the bulb  140 . The dose may include sulfur. 
     Upon an initial light-on condition, sulfur in the bulb  140  is present in a solid state. In this case, microwaves generated by the magnetron  110  may be applied to the bulb  140 . Electrons are discharged from argon, and acceleration and collision of the electrons occur as an electric field intensity is increased. Thereafter, as sulfur is converted into plasma via evaporation thereof, a light-on condition is achieved. 
     The present invention provides a plasma lighting system that permits a relatively instantaneous light-on condition immediately after a light-off condition. 
     In a conventional plasma lighting system, the interior of a bulb remains in a high pressure state immediately after a light-off condition. In this case, sulfur in the bulb  140  is present in a gas state. In addition, argon returns to a state before the discharge of electrons. More specifically, the interior of the bulb  140  remains in a high temperature and high pressure state for a predetermined time immediately after a light-off condition. Therefore, reduction in the pressure of the bulb  140  or a change in the electric field intensity is required to implement a light-on condition. 
     To this end, conventionally, a predetermined time (for example, 5 minutes) has been required to reduce the internal pressure of the bulb  140  below a given level via cooling. That is, there is a need for a predetermined time taken until sulfur and argon in the bulb  140  return to a state before an initial light-on condition. 
     Meanwhile, the metallic material  210  may function to reduce an electric field intensity required for electric discharge by discharging thermal electrons. More specifically, the metallic material  210  generates thermal electrons even after a light-off condition of the plasma lighting system  100 , enabling electric discharge. That is, the metallic material  210  functions to discharge thermal electrons in a high temperature and high pressure state upon a light-on condition after a light-off condition. 
     Here, a time taken until a light-on condition after a light-off condition of the plasma lighting system  100  may be 5 minutes or less. Preferably, a time taken until a light-on condition after a light-off condition of the plasma lighting system  100  may be 3 minutes or less. In addition, sulfur may be in a vapor state when the plasma lighting system  100  is again re-lit. That is, even when sulfur is in a vapor state after a light-off condition, a light-on condition may be implemented again without standby time by the metallic material  210 . 
     In addition, the metallic material  210  functions to enable electric discharge in the bulb  140  that remains in a high pressure state. In particular, an instantaneous light-on condition may be accomplished without an increase in the output of microwaves of the plasma lighting system  100 . 
     The metallic material  210  may include one or more of various metals capable of generating thermal electrons even in a high pressure state. 
     In one embodiment, the metallic material  210  may include at least one selected from the group consisting of tungsten (W), tantalum (Ta), molybdenum (Mo), rhenium (Re), lanthanum hexaboride (LaB 6 ), and cerium hexaboride (CeB 6 ). 
     Meanwhile, restriction of reaction between the metallic material  210  and the dose may be important. 
     More specifically, when the metallic material  210  and the dose react with each other, reduction of a flux due to generation of a compound and damage to the bulb  140  or deterioration in the external appearance of the bulb  140  due to the increased surface temperature of the bulb  140  may occur. 
     To prevent these problems, the metallic material  210  may be surrounded by an insulation capsule  220 . That is, the insulation capsule  220  may prevent reaction between the metallic material  210  and the dose. 
     In addition, the insulation capsule  220  may surround the metallic material  210 , and the metallic material  210  may be sealed in a vacuum state within the insulation capsule  220 . 
     In addition, the insulation capsule  220  may be formed of quartz or ceramic. 
     Meanwhile, to restrict reaction between the metallic material  210  and the dose, the bulb  140  may be additionally filled with at least one metal halide. 
     More specifically, the bulb  140  may receive sulfur for generation of light using microwaves, the metallic material  210  for generation of thermal electrons, and the metal halide. 
     In addition, the dose may include a main dose including sulfur and an additive dose including at least one metal halide. 
     The additive dose may include a compound of a metal and a halogen. 
     In one embodiment, the metal may be one selected from the group consisting of scandium (Sc), sodium (Na), titanium (Ti), indium (In), dysprosium (Dy), holmium (Ho), thulium (Tm), potassium (K), calcium (Ca), tin (Sn), antimony (Sb), strontium (Sr), and aluminum (Al). 
     In addition, the halogen may be one selected from the group consisting of chlorine (Cl), bromine (Br), iodine (I), and astatine (At). 
       FIGS. 4 and 5  show simulation results explaining effects of the plasma lighting system  100  according to the present invention. 
       FIG. 4  is a graph showing time taken until a light-on condition based on insertion of the metallic material  210 . 
     Reference numeral T1 designates time taken until a light-on condition in a case in which the metallic material is inserted into the bulb  140 , and reference numeral T2 designates time taken until a light-on condition in a case in which no metallic material is inserted into the bulb  140 . 
     Referring to  FIG. 4 , it can be confirmed that the time taken until a light-on condition after a light-off condition is considerably reduced in a case in which the metallic material is inserted into the bulb  140 . 
     That is, as the metallic material generates thermal electrons in the bulb that remains in a high pressure state after a light-off condition, electric discharge is possible and thus a light-on condition of the plasma lighting system is possible. 
       FIG. 5( a )  shows the distribution and intensity of an electric field in the bulb in which no metallic material is received. In addition,  FIG. 5( b )  shows the distribution and intensity of an electric field in the bulb in which the metallic material is received. 
     Referring to  FIG. 5( a ) , in a case in which no metallic material is received in the bulb, an electric field is relatively uniformly distributed in the bulb. 
     In contrast, referring to  FIG. 5( b ) , in a case in which the metallic material is received in the bulb, an electric field is concentrated on the metallic material inserted into in the bulb, thus causing an electric field intensity required for electric discharge. In addition, filling the bulb with the metallic material may increase the intensity of an electric field in the bulb. 
     In addition, a small quantity of thermal electrons generated by the metallic material may also cause an electric field to be concentrated on the metallic material, thus enabling an instantaneous initial light-on condition. 
     As is apparent from the above description, a plasma lighting system according to one embodiment of the present invention has the following effects. 
     The plasma lighting system includes a metallic material received in a bulb. The metallic material functions to reduce an electric field intensity required for electric discharge by discharging thermal electrons. 
     Accordingly, the plasma lighting system may reduce time taken until a light-on condition after a light-off condition. More specifically, as electric discharge occurs even in a state in which the interior of the bulb remains in a high pressure state, an instantaneous light-on condition is possible. In addition, cooling to reduce the internal pressure of the bulb after a light-off condition is unnecessary. 
     In addition, as an electric field in the interior of the bulb is concentrated on the metallic material, it is possible to achieve an electric field intensity required for electric discharge. 
     In addition, it is possible to achieve a luminous flux of a given level or more and to maintain a desired luminous efficacy by restricting reaction of the metallic material and a main dose (for example, sulfur). 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.