EP1936660A1 - Lampe a decharge a cathode chaude, unite de lampe et dispositif d'affichage - Google Patents

Lampe a decharge a cathode chaude, unite de lampe et dispositif d'affichage Download PDF

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Publication number
EP1936660A1
EP1936660A1 EP06797810A EP06797810A EP1936660A1 EP 1936660 A1 EP1936660 A1 EP 1936660A1 EP 06797810 A EP06797810 A EP 06797810A EP 06797810 A EP06797810 A EP 06797810A EP 1936660 A1 EP1936660 A1 EP 1936660A1
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EP
European Patent Office
Prior art keywords
lamp
hot cathode
cathode discharge
krypton
glass bulb
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06797810A
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German (de)
English (en)
Inventor
Shiro c/o Matsushita Electric Ind. Co. Ltd. IIDA
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Panasonic Corp
Original Assignee
Panasonic Corp
Matsushita Electric Industrial Co Ltd
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Filing date
Publication date
Application filed by Panasonic Corp, Matsushita Electric Industrial Co Ltd filed Critical Panasonic Corp
Publication of EP1936660A1 publication Critical patent/EP1936660A1/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/067—Main electrodes for low-pressure discharge lamps
    • H01J61/0672—Main electrodes for low-pressure discharge lamps characterised by the construction of the electrode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/067—Main electrodes for low-pressure discharge lamps
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/12—Selection of substances for gas fillings; Specified operating pressure or temperature
    • H01J61/16—Selection of substances for gas fillings; Specified operating pressure or temperature having helium, argon, neon, krypton, or xenon as the principle constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/12—Selection of substances for gas fillings; Specified operating pressure or temperature
    • H01J61/18—Selection of substances for gas fillings; Specified operating pressure or temperature having a metallic vapour as the principal constituent
    • H01J61/20—Selection of substances for gas fillings; Specified operating pressure or temperature having a metallic vapour as the principal constituent mercury vapour
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/30—Vessels; Containers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/30—Vessels; Containers
    • H01J61/305—Flat vessels or containers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/30—Vessels; Containers
    • H01J61/33—Special shape of cross-section, e.g. for producing cool spot
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/70—Lamps with low-pressure unconstricted discharge having a cold pressure < 400 Torr
    • H01J61/72—Lamps with low-pressure unconstricted discharge having a cold pressure < 400 Torr having a main light-emitting filling of easily vaporisable metal vapour, e.g. mercury
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/24—Means for obtaining or maintaining the desired pressure within the vessel
    • H01J61/28—Means for producing, introducing, or replenishing gas or vapour during operation of the lamp

Definitions

  • the present invention relates to a hot cathode discharge lamp, as well as a lamp unit and a display apparatus that include the hot cathode discharge lamp as a light source.
  • cold cathode discharge lamps are used as a light source in backlight units of liquid crystal displays. Due to being well-suited to reductions in diameter, cold cathode discharge lamps are favorably used as a light source in backlight units for which thinness is demanded. Meanwhile, as liquid crystal displays increase in size, higher efficiency is demanded for lamps used as a light source in the backlight units of liquid crystal displays. Although mainly cold cathode discharge lamps are currently used as a light source in backlight units, focus has begun to be placed on using hot cathode discharge lamps, which are even more efficient than cold cathode discharge lamps, as new light sources in backlight units.
  • Patent document 1 discloses a hot cathode discharge lamp in which the transverse cross section of a circular glass bulb has a flattened shape. Patent document 1 recites that such a structure enables increasing the direct illuminance of a lighting apparatus using the hot cathode discharge lamp, thereby increasing the luminous efficacy of a lamp. Also, patent document 2 discloses technology for improving the brightness uniformity of a fluorescent lamp used as a light source in a backlight unit without reducing the brightness of the backlight unit, by giving the transverse cross section of the glass bulb an elliptical shape.
  • hot cathode discharge lamps have a short lamp lifetime, which is a problem when they are used as a light source in a backlight unit.
  • the present invention has been achieved in view of the above problem, and an aim thereof is to provide a hot cathode discharge lamp, a lamp unit, and a display apparatus that have a long lifetime.
  • the inventors of the present invention performed diligent research in order to extend the lifetime of a hot cathode discharge lamp used as a light source in a backlight unit for which thinness is demanded.
  • the inventors focused their attention on the fact that the lifetime of a hot cathode discharge lamp depends on the amount of an emitter applied to the electrode coils. Specifically, the inventors took note of the fact that when the same amount of an emitter is applied per electrode coil unit length, the lifetime of the lamp increases in proportion to the length of the electrode coils.
  • the diameter of the glass bulb that is the envelope for the hot cathode discharge lamp must also be increased. Yet it is not desirable to increase the diameter of the glass bulb since thinness is demanded for the backlight unit.
  • the present invention is a hot cathode discharge lamp including: a glass bulb whose cross section perpendicular to a tube axis of the glass bulb is flattened in shape; and an electrode coil arranged in the glass bulb such that an axis of the electrode coil is pointed in a direction of a major inner diameter of the flattened shape, wherein a length L of the electrode coil in a direction of the axis thereof satisfies a relationship L2 ⁇ L ⁇ L1, where L1 is a length of the major inner diameter of the flattened shape and L2 is a length of a minor inner diameter of the flattened shape.
  • the thickness of a backlight unit can be reduced by disposing the hot cathode discharge lamp such that the minor inner diameter of the glass bulb is pointed in the thickness direction of the backlight unit.
  • the axis of the electrode coil is pointed in the major diameter direction of the glass bulb, and the electrode coil length L is longer than the minor inner diameter length L2 of the glass bulb, thereby enabling a longer lifetime than a hot cathode discharge lamp that has a circular cross section of the same width (diameter L2).
  • flattened shape refers to a shape in which a glass tube with a circular cross section is squashed in an up-and-down direction such that the inner diameter in the up-and-down direction is the minor inner diameter and the inner diameter in the left-and-right direction is the major inner diameter.
  • the "flattened shape” may be an elliptical shape in which the entire outline is composed of a curved line. Also, the inventors of the present invention performed diligent research in order to extend the lifetime of a hot cathode discharge lamp for a backlight unit.
  • the inventors focused their attention on the fact that as the partial pressure rate of the krypton used as a buffer rare gas is increased, lamp lifetime is extended.
  • lamp output total luminous flux
  • the inventors found that the problem in which the lamp output decreases as the partial pressure rate of krypton is increased occurs when a hot cathode discharge lamp is operated in a room temperature atmosphere, but does not occur when a hot cathode discharge lamp is operated in a 50°C to 70°C atmosphere such as when disposed in the housing of a backlight unit.
  • the hot cathode discharge lamp is preferably a hot cathode fluorescent lamp arranged in a housing, wherein the glass bulb is preferably a rare gas enclosed therein, and the rare gas preferably includes krypton at a partial pressure rate of 20% or more.
  • the hot cathode discharge lamp of the present invention is disposed in the housing of the lamp unit, and the temperature of such atmosphere is higher than room temperature, the lamp output is favorable even when krypton is enclosed as a buffer rare gas.
  • the lamp voltage decreases as the krypton partial pressure rate increases, which has advantages such as improving the starting characteristic and facilitating the sustaining of a discharge.
  • the partial pressure rate of the krypton is preferably 60% or less. This is because lamp dimming becomes difficult if the partial pressure rate of krypton in the rare gas mixture exceeds 60%. Since krypton has a higher atomic weight than argon, the mercury enclosed in the envelope diffuses less readily as the krypton partial pressure rate increases, as a result of which the start-up characteristic from starting of the lamp worsens. In view of this as well, the partial pressure rate of krypton in the rare gas mixture is preferably 60% or less. Furthermore, since krypton is far more expensive than argon, enclosing more than the required amount of krypton would lead to a meaningless rise in cost. In view of this as well, the partial pressure rate of krypton in the rare gas mixture is preferably 60% or less. Additionally, when the partial pressure rate of krypton in the rare gas mixture exceeds 60%, so-called moving stripes appear during dimmed lamp operation.
  • the partial pressure rate of the rare krypton is more desirably 45% or more. This structure reduces the lamp voltage, thereby increasing the lamp current, which enables obtaining a very highly efficient lamp.
  • the partial pressure rate of the rare krypton is more desirably 55% or less. This is because it was confirmed by experimentation that lamp efficiency falls if the krypton partial pressure rate exceeds 55%.
  • the present invention is also a lamp unit including: a housing; and any of the above hot cathode discharge lamps, being arranged in the housing.
  • This structure enables obtaining a lamp unit that is highly efficient and has a long lifetime.
  • the present invention is also a display apparatus including the above lamp unit as a light source. This structure enables obtaining a display apparatus that is highly efficient and has a long lifetime and low power consumption.
  • Another display apparatus of the present invention includes a housing; and any of the above hot cathode discharge lamps, being arranged in the housing. This structure enables obtaining a display apparatus that is highly efficient and has a long lifetime and low power consumption.
  • Fig.1 shows the LCD apparatus of the present invention, where a portion has been cut away to show the internal condition thereof.
  • An LCD apparatus 1 is, for example, a liquid crystal color TV, and includes a liquid crystal screen unit 3 and a backlight unit 5 that are incorporated in a housing 4.
  • the liquid crystal screen unit 3 includes, for example, a color filter substrate, liquid crystals, a TFT substrate, and a drive module (not depicted). Color images are displayed on a screen 6 of the liquid crystal screen unit 3 based on an image signal received from a device that is external to the liquid crystal screen unit 3.
  • Fig.2 is a schematic perspective view showing the structure of the backlight unit 5 for a 16:9 aspect ratio LCD, pertaining to the embodiments. A portion of a front panel 16 has been cut away in Fig.2 to show the internal structure of the backlight unit 5.
  • the backlight unit 5 includes a plurality of hot cathode discharge lamps 20, a housing 10 that has an opening and stores the lamps 20, and the front panel 16 that covers the opening of the housing 10.
  • the housing 10 is made of, for example, polyethelyne terephthalate (PET) resin, and a metal such as silver has been vapor-depositing on an inner face 11 to form a reflective surface.
  • PET polyethelyne terephthalate
  • Each of the lamps 20 is shaped as a straight tube, and in the embodiments, 14 of the lamps 20 are arranged in the housing 10 in accordance with a direct-type backlight unit, and are electrically connected in parallel. Constant current control of the lamps 20 is performed by a lighting circuit not depicted in Fig.2 . Note that the structure of the lamps 20 is described later.
  • the translucent front panel 16 is composed of a diffusion plate 13, a diffusion sheet 14, and a lens sheet 15 laminated in the stated order.
  • the opening of the housing 10 is covered by the translucent front panel 16 and hermitically sealed such that foreign objects such dust and dirt cannot enter the interior.
  • the diffusion plate 13 and diffusion sheet 14 of the front panel 16 disperse and diffuse light emitted from the lamps 20, and the lens sheet 15 aligns the emitted light with the normal direction of the lens sheet 15, as a result of which, the light emitted from the lamps 20 shines in a forward direction evenly across the entire surface (emitting face) of the front panel 16.
  • Figs.3A and 3B show the structure of a hot cathode discharge lamp (hereinafter, may be simply called the "lamp") 20, where Fig.3A shows a planar cross section and Fig. 3B shows a transverse cross section taken along A-A.
  • the lamp 20 includes a straight-tube shaped glass bulb 22 and a pair of electrodes 30a and 30b provided at respective ends in the glass bulb 22.
  • the glass bulb 22 is made of barium strontium silicate glass (a soft glass whose softening point is 675°C). As shown in Fig. 3B , a cross section of the glass bulb 22 perpendicular to the tube axis is an ellipse that has a major inner diameter L1 and a minor inner diameter L2.
  • the thickness of the backlight unit 5 can be reduced by arranging the lamp 20 such that the minor inner diameter of the glass bulb 22 is pointed in the thickness direction of the backlight unit 5, that is to say, the minor inner diameter of the glass bulb 22 is arranged perpendicular to the front panel 16. Note that although resulting in an increased thickness, the minor inner diameter of the glass bulb 22 may be arranged parallel to the front panel 16, and a longer lifetime can be achieved in this case as well.
  • an evacuation tube 28 is connected to one end of the glass bulb 22 (in Fig.3A , the left end).
  • the evacuation tube 28 is used when evacuating the interior of the glass bulb 22 and enclosing rare gases therein, and is sealed after the evacuation and enclosing has been performed.
  • Providing the evacuation tube 28 at one end of the glass bulb 22 instead of at both ends facilitates coldest point control. In other words, it is impossible to know where the coldest point is if an evacuation tube is provided at both ends.
  • the portion of the evacuation tube 28 that protrudes outward has a length Li of 10 mm.
  • the length Li is preferably from 5 mm to 30 mm, or more preferably from 15 mm to 30 mm. If Li is less than 5 mm, sealing and cutting of the evacuation tube 28 becomes difficult. Setting the length Li from 15 mm to 30 mm enables improving efficiency by coldest point control. The longer Li is over 30 mm, the more readily breakable the protruding portion becomes, and the larger the non-light-emitting portion becomes, which reduces commercial value. Also, a further improvement in efficiency cannot be expected even if Li is made longer than 30 mm.
  • the electrodes 30a and 30b are so-called glass bead mounted electrodes, and are pinch-sealed (crush sealed) at the ends of the glass bulb 22.
  • the electrodes 30a and 30b are composed of triple-coil electrode coils 31a and 31b having 6.5 turns; pairs of lead wires 32a and 32b, and 33a and 33b that support the electrode coils 31a and 31b spanning therebetween; and bead glass 34a and 34b that supports the lead wires 32a, 32b, 33a, and 33b.
  • the electrode coils 31a and 31b are made of, for example, tungsten, and strontium oxide, calcium oxide, or barium oxide has been applied thereon as an emitter.
  • the axis of the electrode coils 31a and 31b is pointed in the major inner diameter direction, and the length L of the electrode coils 31a and 31b is longer than the minor inner diameter L2 and shorter than the major inner diameter L1.
  • a protective film 24 composed of alumina has been formed on the inner face of the glass bulb 22.
  • a phosphor layer 26 has been laminated on the protective film 24.
  • the phosphors in the phosphor layer 26 are a mixture of red (Y 2 O 3 :Eu), green (LaPO 4 :Ce,Tb 3 ) and blue (BaMg 2 Al 16 O 27 :Eu,Mn) light emitting rare earth phosphors.
  • the glass bulb 22 has enclosed therein approximately 5 mg of mercury 21 and argon (Ar) as a buffer rare gas at a pressure of 500 Pa at room temperature.
  • the mercury 21 enclosed in the glass bulb 22 may be mercury in an amalgam form such as zinc mercury, tin mercury, bismuth mercury, or indium mercury.
  • the glass bulb 22 has a major inner diameter L1 of 17 mm, a minor inner diameter L2 of 10 mm, an overall length L o of 1010 mm, an inter-electrode distance Le of 950 mm, and a bulb wall loading We of 0.05 (W/cm 2 ).
  • the bulb wall loading is a value obtained by dividing the lamp power by the internal surface area of the portion of the glass bulb 22 that corresponds to the inter-electrode distance Le. Note that in order to obtain a lamp having a long lifetime, the bulb wall loading We of the lamp 20 is preferably specified in the range of 0.025 to 0.07 (W/cm 2 ).
  • the bulb wall loading is greater than 0.07 (W/cm 2 )
  • the luminous flux degrades intensely in a short time period and a long lifetime cannot be obtained.
  • the bulb wall loading is less than 0.025 (W/cm 2 )
  • an excessively large lamp tube diameter is required to obtain the necessary luminous flux while maintaining a fixed lamp power, and such an excessively large lamp tube is not suitable for use in a backlight unit.
  • the power is reduced while maintaining a fixed lamp size, it becomes difficult to sustain a discharge.
  • the above described lamp 20 in this case has a lamp voltage of 125 V, a lamp efficacy of 81 lm/W, and an average lifetime of 39,000 hours.
  • a manufacturing method for the lamp 20 First, a straight glass tube having a circular cross section perpendicular to the tube axis is prepared. After cleaning and drying the glass tube, a known method is used to form a protective film by applying alumina to the inner face of the glass bulb and drying the applied alumina. Furthermore, a phosphor suspension is applied onto the protective film and dried, according to a known method.
  • Figs. 4A to 4D illustrate steps for transforming the cross section of the glass tube perpendicular to the tube axis from a circular to an elliptical shape.
  • Fig.4(a) there are provided elliptical cavity dies 25a and 25b made of stainless steel.
  • Fig.4(b) the glass tube is placed between the dies 25a and 25b so as to be sandwiched therebetween, while maintaining the temperature of the glass tube.
  • the cross section of the glass tube 23 is transformed into an elliptical shape by the weight of the die 25a. This enables obtaining the glass bulb 22 having an elliptical cross section such as shown in Fig.4(d) .
  • the cross section of the glass tube is transformed from a circular shape to an elliptical shape when scintering the phosphors, thereby achieving a simpler manufacturing process than a case of performing a separate step of heating the glass tube to transform its shape.
  • using a glass tube having a circular cross section and an inner diameter of 15 mm enables obtaining a glass bulb whose cross section is elliptical and has a major inner diameter L1 of 17 mm and a minor inner diameter L2 of 10 mm.
  • a glass tube having a circular cross section and an inner diameter of 20 mm enables obtaining a glass bulb whose cross section is elliptical and has a major inner diameter L1 of 24 mm and a minor inner diameter L2 of 16 mm.
  • the inner diameter dimensions of the glass bulb can be adjusted to various values by changing the glass bulb material.
  • the phosphor layer 26 shown in Figs.3A and 3B is formed by stripping away the phosphor from unnecessary portions of the glass bulb 22.
  • the electrodes 30a and 30b are sealed to the glass bulb 22 using a known pinch-sealing method, the mercury 21 and the buffer rare gas are introduced, the glass bulb 22 is evacuated via the evacuation tube 28, and the evacuation tube 28 is sealed, thereby obtaining the lamp 20.
  • the axis of the electrode coils 31a and 31b is pointed in the major diameter direction of the glass bulb 22, and the length L of the electrode coils 31a and 31b is longer than the minor inner diameter length L2 of the glass bulb.
  • the lamp lifetime is substantially in proportion to the length (or number of turns) of the electrode coils. Therefore, the structure of the lamp 20 pertaining to the present embodiment can achieve a longer lifetime than a hot cathode discharge lamp having a circular cross section of the same width.
  • the thickness of the backlight unit 5 can be reduced by arranging the hot cathode discharge lamp such that the minor inner diameter of the glass bulb is pointed in the thickness direction of the backlight unit 5.
  • conventional backlight units use cold cathode discharge lamps as a light source, and since the normal lamp efficacy of cold cathode discharge lamps is approximately 50 lm/W, the efficiency of such backlight units is low.
  • the backlight unit 5 pertaining to the present embodiment uses the hot cathode discharge lamps 20 as a light source, and since the lamp efficacy of the hot cathode discharge lamps 20 is approximately 80 lm/W, the backlight unit 5 is very highly efficient.
  • the distance from the lamps 20 in the housing 10 of the backlight unit 5 to the liquid crystal panel can be increased with respect to the length of the electrode coils 31a and 31b since the glass bulbs 22 are elliptical in shape.
  • the inter-lamp interval at which the lamps 20 are arranged in the housing 10 can be increased, thereby enabling a reduction in the number of lamps 20 necessary as the light source.
  • This structure enables cutting down the number of parts required for the backlight unit 5, thereby contributing to a reduction in the cost of the backlight unit 5.
  • Fig.2 illustrates a structure in which 14 of the lamps 20 are provided, the number of lamps 20 disposed in the housing 10 of the backlight unit 5 may be changed to suit the screen size etc. of the LCD apparatus.
  • Embodiment 2 is the same as embodiment 1 with the exception of the components of the buffer rare gas, and therefore a description of portions other than the components of the buffer rare gas has been omitted.
  • the inventors of the present invention performed diligent research in order to further extend the lifetime, of hot cathode discharge lamps used as a light source in a backlight unit.
  • the inventors used a mixture of krypton and argon as the buffer rare gas, and focused their attention on the fact that lamp lifetime is extended as the partial pressure rate of the krypton is increased.
  • the lamp lifetime is extended as the partial pressure rate of krypton is increased because instead of using mainly argon, as is common, the partial pressure rate of krypton, which has a higher atomic weight than argon, is increased, which makes it difficult for the emitter to disperse off of the electrode coils.
  • lamp output total luminous flux
  • the maximum partial pressure rate of krypton has been approximately 15%.
  • the inventors found that the problem in which the lamp output decreases as the partial pressure rate of krypton is increased occurs when a hot cathode discharge lamp is operated in a room temperature atmosphere, but does not occur when a hot cathode discharge lamp is operated in an 50°C to 70°C atmosphere such as when disposed in the housing of a backlight unit.
  • Fig.5 is a table showing the relationship between lamp lifetime and the partial pressure rate of krypton in the buffer rare gas mixture. Note that “ ⁇ ” (a circle) in the "moving stripes at 30% dimming” column indicates that moving stripes did not appear, and “ ⁇ " (an X) in the same column indicates that moving stripes appeared. Also, in the “start-up characteristic” column, “ ⁇ " (a circle) indicates a favorable state, “ ⁇ " (a triangle) indicates an acceptable state, and “ ⁇ " (an X) indicates a poor state.
  • the partial pressure rate of krypton in the buffer rare gas mixture it is preferable for the partial pressure rate of krypton in the buffer rare gas mixture to be 20% or more since lamp lifetime exceeds 50,000 hours in such a case.
  • the lamp voltage decreases as the krypton partial pressure rate increases, which has advantages such as improving the starting characteristic and facilitating the sustaining of a discharge.
  • the rate power is constant (e.g., 20 W)
  • the higher the krypton partial pressure rate is raised the lower the lamp voltage decreases and the higher the lamp current increases.
  • the temperature of the electrode coils 31a and 31b must be raised in order to cause electrons to be emitted from the applied emitter during lamp operation, and the electrode coils 31a and 31b cannot be sufficiently heated solely by the lamp current.
  • a separate filament current is applied to the electrode coils 31a and 31b, which are heated by the flowing filament current.
  • the lower the lamp current the greater the filament current must be in order to raise the temperature of the electrode coils 31a and 31b.
  • the filament current is applied separately and in addition to the lamp power, from the viewpoint of suppressing power consumption, it is desirable to increase the lamp current as much as possible in order to reduce the amount of filament current that is required.
  • raising the krypton partial pressure rate reduces the lamp voltage and increases the lamp current, thereby lowering the required amount of filament current and suppressing energy loss.
  • the inventors also found that lamp dimming becomes slightly difficult when the krypton partial pressure rate exceeds 60%, and the krypton partial pressure rate is therefore preferably 60% or less. Note that although dimming becomes slightly difficult when the krypton partial pressure rate exceeds 60%, since the lifetime is extended as the partial pressure rate of krypton is increased, it is desirable to determine the krypton partial pressure ratio taking into consideration the demands for both a long lifetime and favorable dimming characteristics.
  • the mercury enclosed in the glass bulb 22 diffuses less readily as the krypton partial pressure rate increases, as a result of which the start-up characteristic from starting of the lamp worsens.
  • the partial pressure rate of krypton in the rare gas mixture is preferably 60% or less. Note that the start-up characteristic results shown in Fig.5 were measured visually.
  • the partial pressure rate of krypton in the rare gas mixture is preferably 60% or less. Additionally, when the partial pressure rate of krypton in the rare gas mixture exceeds 60%, so-called moving stripes appear during dimmed lamp operation.
  • Fig.6 diagrammatically shows moving stripes that appear during dimmed lamp operation, and is used to illustrate the above-mentioned moving stripes.
  • Moving stripes are a phenomenon in which, when the lamp 20 is operated, alternating light portions and dark portions appear in part or all of the lamp 20, thereby forming a striped pattern, and such stripes move toward either one of the tube ends in the lamp 20.
  • the striped pattern is moving from the right side of the page to the left side of the page.
  • the partial pressure rate of krypton in the rare gas mixture enclosed in the glass bulb 22 is 45% or more. This structure enables sufficiently reducing the lamp voltage and raising the lamp current, thereby obtaining a very highly efficient lamp. Also, as shown in Fig.5 , since experimentation confirmed that lamp efficiency somewhat drops when the krypton partial pressure rate exceeds 55%, the krypton partial pressure rate is desirably 55% or less. This is thought to be because of the following. Up to a krypton partial pressure rate of 45%, energy loss can be suppressed by the reduction in filament current that accompanies the increase in lamp current. However, when the krypton partial pressure rate exceeds 55%, the lamp current becomes too large and is consumed as heat when flowing through the electrode coils 31a and 31b, which increases the amount of energy loss.
  • the inventors of the present invention manufactured a backlight unit whose light source was hot cathode discharge lamps including 50% argon and 50% krypton as buffer rare gases, and upon testing the lamp, did not find any problems regarding a reduction in lamp output. Also, a highly efficient backlight unit can be obtained since hot cathode discharge lamps are used as a light source. As described above, the present invention enables providing a hot cathode discharge lamp, lamp unit, and LCD apparatus that are highly efficient and have a long lifetime.
  • the glass bulb 22 is described above as being straight in shape from an external viewpoint, the present invention is not limited to this.
  • the glass bulb 22 may have another shape such as a "U” shape or the shape of a "U” whose bottom line is straight.
  • the display apparatus may be, for example, a signboard apparatus that includes a housing and a hot cathode discharge lamp of either of the embodiments disposed in the housing.
  • the present invention is widely applicable to hot cathode discharge lamps. Also, the present invention can provide a hot cathode discharge lamp, lamp unit, and display apparatus that are highly efficient and have a long lifetime, and therefore has a high industrial utility value.

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  • Discharge Lamp (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)
EP06797810A 2005-09-13 2006-09-11 Lampe a decharge a cathode chaude, unite de lampe et dispositif d'affichage Withdrawn EP1936660A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2005265793 2005-09-13
PCT/JP2006/318003 WO2007032320A1 (fr) 2005-09-13 2006-09-11 Lampe a decharge a cathode chaude, unite de lampe et dispositif d'affichage

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EP1936660A1 true EP1936660A1 (fr) 2008-06-25

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EP (1) EP1936660A1 (fr)
JP (1) JPWO2007032320A1 (fr)
KR (1) KR20080044264A (fr)
CN (1) CN101263576A (fr)
TW (1) TW200729275A (fr)
WO (1) WO2007032320A1 (fr)

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KR20080044264A (ko) 2008-05-20
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WO2007032320A1 (fr) 2007-03-22
JPWO2007032320A1 (ja) 2009-03-19

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