Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J63/00—Cathode-ray or electron-stream lamps
  • H01J63/06—Lamps with luminescent screen excited by the ray or stream

Definitions

• the present invention relates to lighting, and more particularly to a lighting apparatus employing a suitable phosphor in combination with a cold cathode field emitter.
• This invention is the result of a contract with the U.S. Department of Energy (Contract No. W-7405-ENG-36).
• Fluorescent lighting has been the standard illumination method in commercial buildings for many years. While it is used in a lessor degree in homes, it is generally applied where large areas need to be economically lighted. Although incandescent tungsten lighting is less efficient and more costly than fluorescent lighting, incandescent bulbs are the primary method of home lighting because of superior convenience and ascetics.
• fluorescent lighting is a highly efficient method of lighting, it does suffer from several deficiencies. Among these deficiencies are ecological concerns. Fluorescent light tubes are now classified as hazardous materials by the U.S. Environmental Protection Agency (EPA) as these tubes contain mercury, a highly toxic and regulated material. This problem has lead to developments such as in U.S. Patent Nos. 5,229,686 and 5,229,687 which describe the potential leaching problems of the mercury from such lights and the addition of a chemical agent to these lights for reaction with the mercury upon pulverization of the light. Further, the ballast resistor required in most, if not all, fluorescent lighting systems can contain polychlorinated biphenyl oils (PCB'S), such materials being highly carcinogenic materials also regulated by the EPA.
• PCB'S polychlorinated biphenyl oils
• the production of light in a fluorescent bulb takes several steps. First, liquid mercury within the tube is electronically heated to volatilize at least some of the mercury. Then, an electric current is passed through the mercury vapor to excite the mercury into a plasma state. The excited mercury plasma emits ultraviolet (UV) light. Finally, the UV light strikes a phosphor in the bulb with the phosphor converting the UV light energy into emitted visible light.
• UV light strikes a phosphor in the bulb with the phosphor converting the UV light energy into emitted visible light.
• This light production pathway has certain performance shortcomings. In comparison to conventional incandescent tungsten lighting systems, fluorescent lighting systems are slow to start as the mercury must first be heated to provide mercury vapor. Also, fluorescent lights are known to make acoustic noise due to the transformer and ballast register electronics needed to start and keep the current flowing through the mercury vapor.
• Oscillation in light output from fluorescent lighting can occur when the system is cold and first turned on thereby distracting some people.
• fluorescent lighting systems are typically incompatible with conventional dimming technology used to adjust the light brightness output necessitating expensive dimmable fluorescent lighting using more exotic electronics.
• U.S. 4,818,914 discloses a lamp comprising a cathode formed with an array of needle-like members projecting from one surface thereof, an accelerator electrode formed with an array of apertures there through, a layer of phosphor and an anode electrode. Voltages applied across the cathode and the accelerator electrode and across the cathode and the anode result in field emission from the cathode and collection of the electrons by the anode. Impingement of the electrons on the phosphor layer results in the emission of light.
• Dworsky et al., U.S. 5,180,951 discloses a uniform light source comprised of a substantially planar (flat) polycrystalline diamond film electron emitter. Y.
• Taniguichi et al., WO 94/28571 disclose a fluorescent tube light source comprising a layer of amorphic diamond film deposited over a conductive filament and an anode surrounding this filament and film which radiates light when struck by the emitted electrons.
• the amorphic diamond film is said to be comprised of a plurality of distributed localized electron emission sites, each sub-site having a plurality of subregions with differing electron affinities between sub-regions.
• US-A-3 866 077 discloses a carbon filament used for the emission of electrons from the tip or end of the constituent carbon fibres.
• EP-A-0 102 139 discloses cathodoluminescent light sources and electrical lighting arrangements including such sources.
• Still another object of the present invention is to provide a low voltage, low power backlight.
• the present invention provides a lighting apparatus including a fibrous cold cathode field emitter wherein fibers of said cold cathode have a diameter of less than 100 microns, an anode for reaction of electrons emitted by the fibrous cold cathode field emitter, a phosphor capable upon contact with emitted electrons from the cold cathode field emitter of generating a persistent light, an evacuated enclosure of less than 133,3 ⁇ 10 -5 Pa (10 -5 Torr) containing within the enclosure the cold cathode field emitter, the anode and the phosphor.
• the persistent light preferably has a luminous intensity of at least 20 lumens per watt.
• FIGURE 1 shows an elongated tube device in accordance with the lighting apparatus of the present invention.
• FIGURE 2 shows an exploded view of a flat plate device in accordance with the lighting apparatus of the present invention.
• FIGURE 3 shows a bulb device in accordance with the lighting apparatus of the present invention.
• FIGURE 4 shows a light beam producing device in accordance with the lighting apparatus of the present invention.
• FIGURE 5 shows a test device in accordance with the lighting apparatus of the present invention.
• FIGURE 6 shows driver circuits for the lighting device of the present invention.
• FIGURE 7 shows a bulb device for use in standard light bulb sockets.
• the present invention relates to a field emission lighting apparatus and to a fiber field emission lighting (FFEL) apparatus.
• FFEL fiber field emission lighting
• the lighting apparatus of the present invention uses field emission to generate light output from a phosphor, e.g., a cathodoluminescent material.
• the field emission lighting apparatus involves a fibrous cold cathode field emitter.
• the field emission electron emitting material can be any material that can be provided in the form of a fiber.
• the field emission electron emitting material of the fibrous cathode is diamond, diamond-like carbon or glassy carbon. Diamond is especially preferred.
• the fibrous cathode is formed of one or more diamond, diamond-like carbon or glassy carbon composite fibers consisting essentially of diamond, diamond-like carbon or glassy carbon on non-diamond core fibers.
• the non-diamond core can be made of a conductive or semi-conductive material.
• the core can be made of a non-conductive material surrounded by a film coating of a conductive or semi-conductive material.
• the core material in the diamond fiber can be, e.g., a conductive carbon such as graphite or a me al such as tungsten, or can be, e.g., silicon, copper, molybdenum, titanium or silicon carbide.
• the core may consist of a more complex structure, for example. a non-conductive material surrounded by a thin coating of conductive or semi-conductive material. A diamond, diamond-like or glassy carbon layer is then coated on the sheath.
• the non-conductive core can be a synthetic fiber such as nylon, KEVLAR® (KEVLAR® is a registered trademark of E. I. du Pont de Nemours and Company, Wilmington, DE), or polyester or inorganic materials such as ceramics or glass.
• a diamond, diamond-like carbon or glassy carbon precursor can be coated onto the non-diamond core or the core can be a diamond, diamond-like carbon or glassy carbon precursor and the diamond, diamond-like carbon or glassy carbon is then formed by appropriate treatment of the precursor.
• the field emission lighting apparatus involves a fibrous cold cathode field emitter which can be of the type described by Valone, in US-A-5 602 439 (U.S. patent application serial number 08/196,343, filed February 14, 1994,) entitled “DiamondGraphite Field Emitters” or by Blanchet-Fincher et al., in US-A-5 570 901 (U.S. patent application serial number 08/387,539, filed February 13, 1995), entitled “Diamond Fiber Field Emitters” which is a continuation-in-part of Valone et al., U.S.
• the cold cathode field emitter can be any other suitable emitting fibrous material such as a suitable graphite fiber treated by exposure to intense ion beam treatment or a suitable graphite fiber treated by exposure to a laser as described by Friedmann, in U.S. provisional patent application number 60/002,277, entitled “Method for Creation of Controlled Field Emission Sites” filed August 14, 1995, or a diamond-coated or diamond-like-coated nickel-coated KEVLAR® fiber as described in US-A-5 578 901 (U.S.
• the fibrous cold cathode may generally be of an conductive material having an activated surface, i.e., capable of allowing electrons to be drawn off at a relatively low bias voltage, with suitable dimensions, i.e., diameters of generally less than 100 ⁇ m (microns), preferably less than 15 ⁇ m (microns), and more preferably less than 10 ⁇ m (microns).
• suitable materials may be included thin fibers of magnesium oxide and the like, suitably with an activated surface based on treatment of the fibers by, e.g., flash heating.
• the fibers of the fibrous cathode each have diameter of less than 100 ⁇ m (microns), preferably less than 15 ⁇ m (microns), and more preferably less than 10 ⁇ m (micron). Smaller diameter fibers reduce the voltage necessary to generate the field emission. Preferably, the diameter exceeds 1 ⁇ m (micron).
• diameters of the fibers of the cold cathodes are substantially smaller in dimensions than the metallic filaments commonly used in presently available lighting apparatus. While a single fiber can be used as the fibrous cathode, it is generally preferred to use more than a single fiber as the fibrous cathode to provide redundancy in electron emission.
• the phosphor used in the lighting apparatus of the present invention can generally be of any type suitable to generate visible light upon being struck by electron emission.
• the phosphor can be zinc oxide:zinc, zinc sulfide, cadmium sulfide, zinc cadmium sulfide, zinc selenide, zinc cadmium selenide yittrium silicate:cesium, zinc phosphate:maganese, or other well known materials which emit light following suitable excitation. Blends or combinations of phosphors may also be employed.
• the phosphor used in the present invention is further capable of producing a persistent light, i.e., the light from a particular point of the phosphor does not readily fade with time as it is excited. Additionally, the output from the excited phosphor may be capable of generating this persistent visible light with a luminous intensity of at least 20 lumens per watt.
• the lighting apparatus of the present invention includes a fibrous cold cathode field emitter, a phosphor, an anode for attraction of emitted electrons from the cold cathode field emitter, all generally contained within an evacuated enclosure. Unlike a standard mercury vapor fluorescent light, the lighting apparatus of the present invention can turn on instantly without the need for heating the mercury to form a plasma. Without the need for maintaining a plasma, the light generated by the lighting apparatus of the present invention can be readily and easily dimmed or brightened by adjustment of the voltage applied to the fiber. When more voltage is applied, more electrons are emitted and impinge upon the phosphor material resulting in additional light output, i.e., a brighter light.
• a current limiting circuit can consist, e.g., of a small resistor/inductor in series with the fibrous cold cathode.
• the evacuated enclosure typically maintains a low pressure of least as low as 133,3 ⁇ 10 -5 Pa (10 -5 Torr).
• Such an evacuated enclosure can be, e.g., a glass bulb or multiple glass sheets with appropriate spacer material therebetween.
• the lighting apparatus of the present invention uses electron emission induced by a directed, shapable applied field. This is in contrast with lighting using a plasma which results in a non-directed light source. This allows practical, but varied, shape configurations of the present lighting apparatus without limitations to the traditional elongated tube. No matter what shape the lighting apparatus has, electron emission from the fibers of the fibrous cathode occurs along the length of the fibers utilized and not from the fiber tip or end.
• a light 10 included a glass tube 12 as an evacuable enclosure.
• the inner or interior surface of glass tube 12 can be coated with a transparent conductor as an anode and a phosphor or cathodoluminescent material 13 .
• a fibrous cathode element 14 is situated within glass tube 12 .
• An end cap 16 includes electrodes connected to fibrous cathode element 14 and to the transparent conductor coating or anode.
• the fibrous cathode element can consist of a single fiber, can include a multiple of fibers or can include a thicker single fiber.
• the single fiber or individual fibers making up the multiple fibers can have a diameter of from 1 micron to 20 microns, preferably 5 microns to 10 microns.
• the glass tube can be a circular cylinder as shown or it can have a configured surface.
• light 20 has a flat plate design with a flat plate 22 having a fibrous cathode element array 24 thereon.
• a transparent second flat plate 26 includes a coating of transparent conductor 28 upon the surface of flat plate 26 facing cathode element array 24 and a coating of a phosphor or cathodoluminescent material 30 upon transparent conductor coating 28 .
• a spacer plate 32 separates flat plate 22 and flat plate 26 and provides an evacuable enclosure for fibrous cathode element array 24 , transparent conductor coating 28 and phosphor or cathodoluminescent material 30 .
• Conductor electrodes are connected to transparent conductor coating 28 and fibrous cathode element array 24 .
• a bulb-shaped light 40 includes a glass globe 42 having an interior coating of a transparent conductor 44 and a coating of a phosphor or cathodoluminescent material 46 .
• a fibrous cathode element 48 the fibrous field emitter, is situated within glass globe 42 .
• Conductors are connected to fibrous cathode element 48 and to the transparent conductor coating or anode 44 .
• the fibrous cathode element 48 can consist of a single fiber or can include a multiple of fibers. Generally, the single fiber or individual fibers making up the multiple fibers can have a diameter of from 1 ⁇ m (micron) to 20 microns, preferably 5 ⁇ m (microns) to 10 ⁇ m (microns).
• a light 50 capable of producing a light beam output 52 includes glass hemispherical support 54 having coatings upon the concave inner surface of a reflector material 56 , a transparent conductive material 58 , and a phosphor or cathodoluminescent material 60 .
• a fibrous cathode element 62 the fibrous field emitter, is situated within glass hemisphere 54 .
• Conductors are connected to fibrous cathode element 62 and to the transparent conductor coating or anode 58 . Varying the shape of the glass suppon 54 can result in a more concentrated light beam. For example, a parabolic support would accomplish this result.
• Figure 5 shows a simple test device used to test field emission variables of the fibrous cathodes including a clear plastic, e.g., Lucite® plastic, tube 70 capped with end caps 72 and 74 to form an evacuable enclosure.
• End cap 72 includes an opening 76 connected to a vacuum pump.
• a grounded copper screen mesh 78 coated with a phosphor or cathodoluminescent material 80 .
• a fibrous cathode element 82 is situated within grounded copper screen mesh 78 .
• Conductors are connected to fibrous cathode element 82 and to copper screen mesh or anode 78 .
• This test device can prove useful for determining emission uniformity of emissive fibers.
• FIG. 6 shows a current limiting circuit for use with the lighting apparatus of the present invention.
• the current limiting circuit 90 includes resistor 92 and an inductor 94 in series with the emissive fiber or fibrous cathode element 96 .
• Power source 98 is connected through a rectifying voltage step-up circuit 100 to the anode 102 and the current limiting circuit 90 in series with cathode element 96 .
• light 120 is in the form of a standard light bulb with a screw type base.
• the inner surface of the glass bulb 121 is coated with a transparent conducting oxide 122 and a phosphor or cathodoluminescent material 123 .
• a fibrous cathode field emitter comprised of a field emission electron emitting fiber 124 is in the central region of the bulb.
• the fiber emitter is shown in a triangular configuration but could be in other configurations, e.g., a circle or a figure having four or more sides.
• the fiber emitter is supported by a non-emitting current carrier 125 . Emitted electrons are shown by the arrows 126 .
• the screw type base 127 is essentially the same as used for standard incandescent bulbs.
• a lighting apparatus was assembled essentially as shown in Figure 5 using a carbon fiber that was exposed to a single intense ion beam treatment.
• the carbon fiber was prepared as follows.
• Untreated graphite fibers (commercially available IM7 graphite fibers from Hercules, Inc., Wilmington, DE) from a graphite yarn were spread out across a frame and the frame placed in the path of an intense ion beam operated in accordance with the teachings of Rej et al., Rev. Sci. Instrum. 64(10), pp. 2753-2760, Oct. 1993.
• the voltage was about 300 kilovolts.
• the distance of the frame from the focus of the ion beam was varied between 15 cm (six inches) to 45 cm (18 inches).
• the energy density of the ion beam was estirnated at from 2 joules per square centimeter to 10 joules per square centimeter.
• the time of a pulse of the ion beam was about one microsecond. After a single pulse, the frame was turned over (180°) and the reverse side of the fibers was exposed to a single pulse of the intense ion beam. The resultant fibers were tested and shown to be excellent field emission electron emitters.
• a fiber was then attached to conductor "A" shown in Figure 5.
• a zinc oxide:zinc phosphor was coated onto the copper mesh screen.
• a potential difference of about 3.5 keV was applied to the cathode and anode, i.e., to conductors "A" and "B".
• a current of 2-3 mA was obtained over a one inch (2.5 cm) length of fiber together with a persistent light emission.
• About 10 watts per inch (2.5 cm) was obtained for lighting purposes.

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• Discharge Lamp (AREA)
• Discharge Lamps And Accessories Thereof (AREA)
• Vessels And Coating Films For Discharge Lamps (AREA)
• Cold Cathode And The Manufacture (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=21699955

Family Applications (1)

Country Status (8)

Cited By (16)

Families Citing this family (14)

Family Cites Families (8)

• 1996
  • 1996-08-12 AU AU70075/96A patent/AU696412B2/en not_active Ceased
  • 1996-08-12 EP EP96931379A patent/EP0845154B1/en not_active Expired - Lifetime
  • 1996-08-12 DE DE69605118T patent/DE69605118T2/de not_active Expired - Fee Related
  • 1996-08-12 WO PCT/US1996/013091 patent/WO1997007531A1/en not_active Ceased
  • 1996-08-12 CA CA002229067A patent/CA2229067A1/en not_active Abandoned
  • 1996-08-12 JP JP9509409A patent/JPH11510951A/ja not_active Ceased
  • 1996-08-12 CN CN96197582A patent/CN1199503A/zh active Pending
  • 1996-08-12 KR KR1019980700278A patent/KR100397720B1/ko not_active Expired - Fee Related

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