HIGH-PRESSURE DISCHARGE LAMP

Abstract: A high-pressure discharge lamp is disclosed having a discharge vessel containing an ionizable filling and having a first and a second electrode, a base having first and second terminals, first and second current conductors electrically coupling said first and second electrodes with said first and second terminals, an outer envelope enclosing said discharge vessel and defining an intervening space therebetween, and a UV-enhancer positioned in the space between the outer envelope and the discharge vessel. The UV-enhancer has an envelope containing an ionizable filling and emitting a ultraviolet radiation, an electrode sealed in said envelope and electrically coupled to said first current conductor, a conducting member electrically coupled to said second current conductor and capacitatively coupled to said envelope, and an insulating sleeve disposed between said conducting member and said envelope to prevent arcing therebetween.

Description: High-pressure discharge lamp. This invention relates to high-pressure discharge lamps having a discharge vessel enclosed by an outer bulb, and more particularly to a metal halide lamp having a starting aid arranged in the intervening space between the outer bulb and the discharge vessel. High pressure discharge lamps, or more particularly metal halide lamps, having starting aids are known in the art. Such lamps are suitable for various applications such as general interior lighting, general exterior lighting, video illumination, etc. The discharge vessel of the known lamp is typically made of quartz glass. Alternatively, this vessel may be made of a ceramic material. Ceramic material in the present description and claims is understood to be a densely sintered polycrystalline metal oxide such as, for example, Al 2 O or YAG and densely sintered polycrystalline metal nitride such as, for example, AIN. A known problem of metal halide lamps is the comparatively wide spread in ignition time. This problem arises from a shortage of free electrons due to the presence of electronegative iodine in the lamp filling. Several methods are known in the art to counteract this problem. For example, the addition of a small quantity of 85 Kr in the discharge vessel can or supplement such a shortage. A disadvantage of Kr as a filling material is its radioactive characteristics. Alternatively, ignition aids, such as a UV-enhancer, are used in metal halide lamps to promote ignition. A UV-enhancer is typically a small discharge tube positioned adjacent the discharge vessel that acts as an ultraviolet radiation source. Such a UN-enhancer has been disclosed in U.S. Patent No. 4,818,915 to Zaslavsky et al. This UV-enhancer has an envelope of UV-transmitting quartz material. Upon breakdown, the UV-enhancer will generate UV-radiation at about 253.7 nm or less. The influence of this UV-radiation leads to the production of free electrons in the discharge vessel, which in turn strongly promotes lamp ignition. The current UV enhancers are placed in such a way that they, upon application of an ignition pulse supplied by a ballast, capacitatively couple energy from one lamp terminal to the other through the UV enhancer gas (or Penning mixture). The UV enhancer must be positioned to provide a minimum gap between the quartz body of the UV enhancer and the opposite potential. This gap reduces arcing through the UV enhancer body which may destroy the UV enhancer itself and the lamp. Furthermore, the orientation between the electrode and emitting plate within the UV enhancer and the opposite potential has an effect on the minimum voltage necessary to create a glow voltage. Thus, assembly of the lamp requires a degree of care in alignment of the UV enhancer=s emitting surface with respect to the opposite potential for optimum performance. Current UV enhancer designs provide no frame support because the enhancers are supported at one end only. Thus, in some lamp types, a separate bridge support structure is necessary. A unique high-pressure discharge lamp is disclosed having a discharge vessel containing an ionizable filling and having first and a second electrodes, a base having first and second terminals, and first and second current conductors electrically coupling said first and second electrodes with said first and second terminals. An outer envelope encloses said discharge vessel and defines an intervening space therebetween. A UV-enhancer is positioned in the space between the outer bulb and the discharge vessel. The UV-enhancer includes, inter alia, an envelope containing an ionizable filling, an electrode sealed in said envelope and electrically coupled to said first current conductor, a conducting member electrically coupled to said second current conductor and capacitatively coupled to said envelope; and an insulating member disposed between said conducting member and said envelope to prevent arcing therebetween. The high pressure discharge lamp is preferably a metal halide lamp with a discharge vessel containing a rare gas, mercury, and a metal halide. In a preferred embodiment, the conducting member may be a ring surrounding the envelope. The conducting member is preferably metallic, e.g. Ni. The insulating member is preferably a cylindrical sleeve positioned between the envelope and the conducting ring. The insulating member may be fabricated from borosilicate glass. It is an object of the invention to provide a lamp having a UV-enhancer that produces a glow discharge at a lower minimum voltage. It is an object of the invention to provide a lamp having a UV-enhancer that provides structural support to the lamp assembly. It is further an object of the invention to provide a lamp having a UV-enhancer that maintain a consistent, optimum separation between the UV-enhancer and the opposite potential to improve ignition characteristics of the lamp and simplify manufacture. These and other features of the lamp according to the invention will become more readily apparent to those skilled in the art from the following detailed description of the subject disclosure. Various embodiments of the subject lamp are explained in more detail with reference to the drawings (not true to scale), wherein: Fig. 1 is a side elevation of a lamp according to the invention; Fig. 2 is a perspective view in enlarged scale of the UV-enhancer according to the invention; and Fig. 3 is a cross-sectional view of the UV-enhancer, taken along lines 3-3 of Fig. 2. Fig. 1 illustrates a preferred embodiment of a high-pressure discharge lamp of the subject disclosure, designated generally by reference numeral 10. Lamp 10 has a discharge vessel 12 which is enclosed by an outer bulb 14 defining an intervening space 16 therebetween. Discharge vessel 12 contains an ionizable filling such as mercury and metal halides as is well known in the art. Lamp 10 further has a lamp base 18 positioned at an end of outer bulb 14. A first current supply conductor 20 provides an electrical connection between a first terminal 25 in lamp base 18 and internal electrode 22 of discharge vessel 12. Likewise, second current supply conductor 24 provides an electrical connection between a second terminal 21 in lamp base 18 and internal electrode 26 of discharge vessel 12. UV-enhancer 28 for emitting ultraviolet radiation is positioned adjacent the first and second current supply conductors 20 and 24 in the intervening space 16 between outer bulb 14 and discharge vessel 22. An envelope 30 contains an ionizable filling and emits ultraviolet radiation in the band of 253.7nm or less to assist ignition of the filling in discharge vessel 12. An electrode 32 is connected at one end to current supply conductor 20, and an intermediate portion is sealed within envelope 30 of UV-enhancer 28. In a preferred embodiment, envelope 30 is constructed of borosilicate glass. A fill material may consist of an inert gas, such as Ar, in combination with a quantity of mercury, such as a Penning mixture. Such an envelope is disclosed in U.S. Patent No. 4,818,915 to Zaslavsky et al., which is incorporated by reference herein. Ultraviolet radiation is produced by the ionizable filling in envelope 30 through capacitative coupling of envelope 30 with a novel conducting member 34 in accordance with the present invention. To promote such ionization, conducting member 34 is positioned adjacent to envelope 30, and is electrically connected to second current conductor 24 by means of connecting wire 36. An ignition pulse is applied to terminals 21 and 25 by an appropriate ballast to initiate ionization within envelope 30. Insulating member 38 is positioned between conducting member 34 and envelope 30. The size and shape of insulating member 38 is selected to maintain a predetermined distance between conducting member 34 and envelope 30 to promote capacitative coupling while preventing destructive arcing therebetween. The UV-enhancer 28 may be assembled as a unit, i.e. insulating member 38 is fixedly positioned between envelope 30 and conducting member 34. As a result, conducting member 34 is maintained at the proper distance from envelope 30 to produce capacitative coupling. The assembled UV-enhancer 38 may be subsequently positioned with respect to the frame of the lamp without the need for critical alignment procedures that are currently required under the prior art. Figures 2 and 3 illustrate UN-enhancer 28 in greater detail. Envelope 30 encloses a cavity 40, defining a discharge space, as will be described below. Wall 42 of envelope 30 is preferably made of borosilicate glass or quarts glass. End portion of envelope 30 is configured with a gas tight seal, around electrode 32. In a preferred embodiment, electrode 32 is fabricated from Kovav. It is alternatively contemplated to fabricate electrode 32 as a Mo wire, with a W end-portion within cavity 34. A molybdenum foil (not shown) may be interposed to form the press seal, or a material may be used to match the thermal expansion characteristics of the quartz glass. An emitting plate 46 may be disposed at an end portion of electrode 32. A combination of a rare gas and Hg, such as a Penning mixture, is suitable as a filling. A pressure is preferably chosen for the filling which accompanies a minimum breakdown voltage. This filling pressure may be readily ascertained experimentally. A fair approximation can be realized by means of the Paschen curve, as is well known in the art. According to a preferred embodiment, envelope 30 has an external length of 25 mm, an external diameter of 4 mm, an internal diameter of 3 mm, and a greatest internal length of 15 mm. The electrode 32 has a diameter of 0.5 mm. The UV-enhancer contains Ar with a filling pressure of 10 t orr . Preferably, the filling pressure lies between 5 and 15 t orr . The insulating member 38 is preferably in the form of a cylindrical sleeve. An insulative material, such as borosilicate glass is appropriate for this purpose. The insulating member 38 is selected for its insulative properties as well as to minimize interference with the ultraviolet radiation from envelope 30. A significant portion of the envelope 30 is not surrounded by the insulating member 38. Preferably, insulating member 38 is affixed to envelope 30 by a temperature resistant cement 50. It is further contemplated that insulating member 38 may be constructed in other shapes and from other materials. Conducting member 34 is positioned over insulating member 38, and is preferably in a circumferential relationship with respect thereto, in the form of a ring or a band. Conducting member 34 is effectively coupled to second current conductor 24 by connecting wire 36. In a preferred embodiment, support member 48 is welded to second current conductor 24 at one end, and affixed to insulating member 38 at the other end. Connecting wire 36 couples conducting member 34 to support member 48. It is alternatively contemplated that connecting wire 36 is directly coupled to second current conductor 24. Conducting member 34 is preferably fabricated from the following materials Ni and stainless steel, and preferably measures approximately 0.8 mm in width and 7 mm in diameter. It is further contemplated that UV enhancer 28 may serve the purpose of structurally supporting the lamp parts as a bridge member between the current conductors 21 and 25. As described above, a fixed connection is established between the envelope 30, the insulating member 38, and the conducting member 34. The enhancer assembly 28 is subsequently welded to the first and second current conductors, thereby providing additional structural rigidity to the lamp assembly, and thus precluding the need for a separate bridge member, as shown in Fig.1. A series of UV-enhancers was subjected to an ignition test. The ignitor circuit comprises a Velonex pulse generator. This starter is widely used for testing the ignition of high-pressure discharge lamps and supplies ignition pulses with a range of pulse heights and widths. In this test, a series of ITs wide pulses were applied with incrementally increasing pulse height. Once a glow discharge was produced in the UV enhancer, the voltage height was recorded. The UN-enhancers were provided with a number of orientations with respect to the frame wire. The UV enhancer, as described above, includes an internal electrode having an emitting plate with a pair of wide surfaces and a pair of narrow surfaces. Positions 1 and 2 were arranged such that the envelope was touching the frame wire. In position 1 , the emitting plate 46 within envelope 30 was oriented such that the wide surface was parallel to the frame wire. In position 2, the wide surface of the plate 46 was oriented perpendicular to the wire. For positions 3 and 4, the envelope was spaced approximately 3mm from the frame wire. In position 3, the plate 46 was oriented such that the wide surface was parallel to the frame wire. In position 4, the wide surface of the plate 46 was oriented perpendicular to the wire. In position 5, the envelope 30 was arranged with the conducting member and insulating member as described above according to the present invention. TABLE 1 The test results are illustrated in Table 1. The minimum glow voltages are shown for 14 different enhancer envelopes oriented in positions 1-4 as described above. Position 5 of the envelope in conjunction with the insulating member and conducting member provides increased emission efficiency as indicated by the reduced minimum glow voltage. The tests show a 400-500V reduction in the voltage required for UV enhancer glow over the conventional UV enhancer mounting.

Claims: CLAIMS: 1. A high-pressure discharge lamp which comprises: • a discharge vessel (12) containing an ionizable filling and having first (22) and a second electrodes (26); • a base (18) having first (25) and second terminals (21); • first (20) and second current conductors (24) electrically coupling said first (22) and second electrodes (26) with said first (25) and second terminals (21); • an outer envelope (14) enclosing said discharge vessel (12)and defining an intervening space (16) therebetween; • a UV-enhancer (28) for emitting radiation primarily in the ultraviolet spectrum positioned in the space (16) between the outer envelope (14) and the discharge vessel (12), characterized in that said UV-enhancer (28) is comprising • an envelope (30)containing an ionizable filling, • an electrode (32) sealed in said envelope (30) and electrically coupled to said first current conductor (20), • a conducting member (34) electrically coupled to said second current conductor (24) and capacitatively coupled to said envelope (30); and • an insulating member (38) positioned between said conducting member (34) and said envelope (30) to prevent arcing therebetween. 2. A high-pressure discharge lamp as recited in Claim 1, wherein said conducting member (34) is fabricated from nickel or stainless steel. 3. A high-pressure discharge lamp as recited in Claim 1 or 2, wherein said conducting member (34) is a ring. 4. A high-pressure discharge lamp as recited in Claim 1 , 2 or 3, wherein said insulating member (38) is a sleeve positioned between said envelope (30) and said conducting 5. A high-pressure discharge lamp as recited in Claim 1,2, 3 or 4 wherein said insulating member (38) is fabricated from borosilicate glass.

Inventors: ALDERMAN JOHN, HARIHARAN ALLEPPEY V, JACKSON ANDREW W, KOWAL ALBERT E, ROBINSON RANDY J, ALDERMAN, JOHN, HARIHARAN, ALLEPPEY, V., JACKSON, ANDREW, W., KOWAL, ALBERT, E., ROBINSON, RANDY, J.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1998
Main classification: H01J61
IPC codes: H01J61