JP2004055521A - Discharge lamp device and backlight using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp in which luminance and luminous efficiency can be improved and a backlight that is suitable for a liquid display device. <P>SOLUTION: The discharge lamp device L comprises a lighting circuit 5 that impresses a voltage on an inner electrode 1 provided inside a light-emitting tube 3 filled with a rare gas and an outer electrode 2a provided at the outside of the light-emitting tube 3. The lighting circuit 5 impresses a positive rectangular wave voltage on the inner electrode 1 with the potential of the outer electrode 2a as the reference potential (OV). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a discharge lamp device for lighting an arc tube, and more particularly to a discharge lamp device for lighting an arc tube containing a rare gas and having a first electrode inside and a second electrode outside. Further, the present invention relates to a backlight provided with such a discharge lamp device.
[0002]
[Prior art]
An arc tube in which a rare gas is sealed, in which an internal electrode is provided, and an external electrode is provided on an outer peripheral surface of the arc tube, a voltage is applied from a lighting circuit connected to the internal electrode and the external electrode. A rare gas discharge lamp device disclosed in Patent Document 1, for example, is disclosed as a discharge lamp device that causes a light emitting tube to emit light by applying a voltage.
[0003]
Further, for example, there are techniques disclosed in Patent Documents 2 and 3 regarding lighting control for a light emitting tube provided with an internal electrode and an external electrode, in which an alternating rectangular wave voltage is applied as a driving voltage.
[0004]
FIG. 14 is a diagram showing a configuration of a conventional discharge lamp device. In the figure, a discharge lamp device 10L is such that a rare gas is sealed in a cylindrical arc tube 103, an internal electrode 101 is provided inside the arc tube 103, and an outer peripheral surface thereof is arranged in the tube axis direction of the arc tube 103. A strip-shaped external electrode 102 is provided along.
[0005]
The internal electrode 101 and the external electrode 102 are respectively connected to a lighting circuit 105, and the arc tube 103 emits light by applying an alternating rectangular wave voltage from the lighting circuit 105.
[0006]
FIG. 15 is a waveform diagram showing an applied voltage waveform and the like in a conventional discharge lamp device. FIG. 3A shows a waveform of an alternating rectangular wave voltage applied between the internal electrode 101 and the external electrode 102, and the vertical axis represents the internal electrode 101 and the external electrode 102 when the potential of the external electrode 102 is used as a reference potential. The applied voltage (V) and the horizontal axis represent time (s).
[0007]
FIG. 15B shows the waveform of the current flowing through the internal electrode 101 and the external electrode 102, wherein the vertical axis represents the current (A) and the horizontal axis represents the time (s). FIG. 3C shows a luminance waveform, and the vertical axis represents luminance (cd / m).²), And the horizontal axis indicates time (s).
[0008]
As shown in FIG. 15 (a), when a voltage of an alternating rectangular wave that becomes a positive voltage and a negative voltage alternately is applied, as shown in FIG. 15 (b), a differential wave shape corresponding to the rising of the positive voltage is obtained. Positive current (rising current) and differential current-shaped negative current (falling current) corresponding to the falling of the negative voltage alternately flow.
[0009]
The phosphor inside the arc tube 103 is excited when a positive current or a negative current flows, and the luminance characteristics shown in FIG. The luminance indicated by the luminance waveform L1 corresponding to the positive current and the luminance waveform L2 smaller than the luminance waveform L1 corresponding to the negative current are obtained.
[0010]
[Patent Document 1]
JP-A-6-163005
[Patent Document 2]
JP-A-2002-75682
[Patent Document 3]
JP 2001-267093 A
[0011]
[Problems to be solved by the invention]
As shown in FIG. 15C, the luminance characteristic when applying a positive voltage (luminance waveform L1) is different from the luminance characteristic when applying a negative voltage (luminance waveform L2) only in the range indicated by the luminance decreasing waveform L4. And the luminous efficiency also decreases. It is considered that when a negative voltage is applied, a contraction discharge occurs, and the luminance decreases due to the effect of reducing the luminance accompanying the contraction discharge.
[0012]
As described above, in the conventional method of applying the alternating rectangular wave voltage, the luminance is reduced every half cycle of the alternating rectangular voltage, so that sufficient luminous efficiency cannot be obtained.
[0013]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a backlight suitable for a discharge lamp device, a liquid crystal display device, and the like having improved luminance and luminous efficiency.
[0014]
[Means for Solving the Problems]
A first discharge lamp device according to the present invention is a discharge lamp device that drives an arc tube in which a rare gas is sealed, a first electrode is provided inside, and a second electrode is provided outside, and the first electrode and the first electrode are connected to each other. A lighting circuit for applying a voltage between the second electrodes is provided. The lighting circuit applies a positive rectangular wave voltage to the first electrode using the potential of the second electrode as a reference potential.
[0015]
A second discharge lamp device according to the present invention is a discharge lamp device for driving an arc tube in which a rare gas is sealed and a first electrode is provided therein, wherein a plurality of second electrodes are arranged in parallel. A support plate that supports the arc tube in proximity to the arc tube, and a lighting circuit that applies a voltage between the first electrode and the second electrode. The lighting circuit applies a positive rectangular wave voltage to the first electrode using the potential of the second electrode as a reference potential.
[0016]
A backlight according to the present invention includes at least one arc tube and the above-described discharge lamp device.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a discharge device and a backlight according to the present invention will be described in detail with reference to the accompanying drawings.
[0018]
<Embodiment 1>
FIG. 1 is a block diagram showing a schematic configuration of a discharge lamp device according to the present invention. The discharge lamp device L includes an arc tube 3 and a lighting circuit 5 for applying a drive voltage to the arc tube 3 to turn on the arc tube 3.
[0019]
The arc tube 3 has a rare gas (inert gas) such as xenon or krypton sealed therein as a discharge gas, and has a LaPO₄: A phosphor such as Ce or Tb is applied. An internal electrode 1 made of nickel or the like is provided inside one end of the arc tube 3. A strip-shaped external electrode 2 a is provided on the outer peripheral surface of the arc tube 3 along the tube axis direction of the arc tube 3. The external electrode 2a is formed by fixing an aluminum tape or a conductive wire to the surface of the arc tube 3, or by applying a conductive material such as a silver paste. When a voltage is applied between the internal electrode 1 and the external electrode 2a of the arc tube 3, a glow discharge is generated inside the arc tube 3, and the rare gas encapsulated therein is shifted to an excited state, and is changed from the excited state to the ground state. The fluorescent material of the arc tube 3 is excited by the ultraviolet light emitted during the transition, and emits visible light.
[0020]
The arc tube 3 is preferably cylindrical and has an inner diameter of 1 mm to 10 mm, a wall thickness of 0.2 mm to 0.5 mm, and a tube length of 100 mm to 300 mm. The reason is that when the discharge lamp device according to the present invention is used as a backlight, it is possible to realize a backlight that is not excessively large in size, secures necessary luminance and luminous efficiency, and is downsized. Because it can be. Further, when applied to a backlight for a liquid crystal display element, a backlight having a shape matching the shape of a small liquid crystal display element can be formed. A lighting circuit 5 is connected to the internal electrode 1 and the external electrode 2a of the arc tube 3.
[0021]
The lighting circuit 5 is obtained by a rectifying circuit C for rectifying the AC voltage supplied from the AC power supply P, a smoothing circuit SC for smoothing the rectified positive voltage to obtain a positive DC voltage, and a smoothing circuit SC. And a switching circuit S for generating a rectangular voltage from the DC voltage boosted by the booster circuit TC. The switching circuit S controls opening and closing of the switch SW, and generates a rectangular voltage from the DC voltage boosted by opening and closing the switch SW.
[0022]
Next, control of the applied voltage (drive voltage) to the arc tube 3 in the lighting circuit 5 will be described.
[0023]
FIG. 2 shows a waveform and the like of a voltage applied to the arc tube 3 by the discharge lamp device L. FIG. 2A is a voltage waveform diagram showing a waveform of a voltage applied between the internal electrode 1 and the external electrode 2a of the arc tube 3, wherein the vertical axis represents the voltage (V) of the applied rectangular wave, and the horizontal axis represents time ( s) are shown respectively. The period during which the positive voltage is applied is T1 and the period of the rectangular wave is T2. FIG. 2B is a current waveform diagram showing a waveform of a current flowing between the internal electrode 1 and the external electrode 2a, wherein the vertical axis represents current (A) and the horizontal axis represents time (s). FIG. 3C is a luminance waveform diagram showing a luminance waveform of the arc tube 3, in which the vertical axis represents luminance (cd / m2) and the horizontal axis represents time (s).
[0024]
In the present invention, as shown in FIG. 2A, the potential of the external electrode 2a is fixed to the reference potential (that is, the voltage is 0 V) with respect to the arc tube 3, and the rectangular waveform of only the positive voltage is applied to the internal electrode 1. Apply voltage. Since the ground potential is preferable as the reference potential, the external electrode 2a is connected to the ground point G that provides the ground potential.
[0025]
In response to the voltage application shown in FIG. 2 (a), as shown in FIG. 2 (b), a positive current (rising current) in the form of a differential wave corresponding to the rising of the positive applied voltage and the falling of the positive applied voltage , A negative current (falling current) in the form of a differential wave alternately flows.
[0026]
The phosphor inside the arc tube 3 is excited when a positive current or a negative current flows, and the luminance characteristics shown in FIG. That is, the luminance indicated by the luminance waveform L1 corresponding to the positive current and the luminance indicated by the luminance waveform L3 corresponding to the negative current are obtained. Here, the luminance waveform L3 during the period in which the applied voltage is 0 V is substantially equal in magnitude to the luminance waveform L1, and the luminance increases in the range indicated by L3a with respect to the conventional luminance waveform L2. As the luminance increases, the luminous efficiency also improves.
[0027]
FIG. 3A shows an emission spectrum of xenon gas, which is one of the discharge gases sealed in the arc tube 3, and FIG. 3B shows one of the phosphors used in the arc tube 3. LaPO₄FIG. 6 is a diagram showing excitation spectra of: Ce and Tb. As shown in FIG. 3A, the emission spectrum has a monomer emission region centered at 147 nm and an excimer emission region centered at 172 nm. The spectral characteristics and the fluorescence shown in FIG. The luminance characteristic of the arc tube 3 is determined by a synergistic effect with the characteristic of the excitation spectrum of the body.
[0028]
As described above, according to the driving method of the applied voltage in the present embodiment, it is possible to prevent the brightness from decreasing every half cycle, which occurs in the conventional method of applying the alternating rectangular wave voltage, so that the brightness is improved and the luminous efficiency is improved. Can be achieved. Although the reason why the luminance can be improved during the period in which the driving voltage is not applied as shown in FIG. 2C is not clear from the complexity of the discharge phenomenon, it is not clear that the contraction discharge is reduced. That the synergistic effect of the monomer emission during the rectangular wave voltage application period and the excimer emission during the period when no voltage is applied effectively acts on the phosphor, and that the internal electrode acts only as an anode to excite the rare gas. It is conceivable that it does not act as a cathode (cathode) that does not occur.
[0029]
Further, as will be described in detail in Embodiment 4, by appropriately controlling the on-duty (T1 / T2) of the rectangular wave composed of only the positive voltage applied to the internal electrode 1, the luminance and the luminous efficiency can be further greatly improved. be able to. This is because, since the spectrum of the excimer light emission region changes due to the change of the on-duty, the luminance can be further improved by the synergistic effect of the emission spectrum of the discharge gas and the excitation spectrum of the phosphor. For example, in the switching circuit S, it is desirable that the opening and closing of the switch SW be PWM-controlled so that the on-duty is 10% or more and 50% or less, and that the carrier frequency be 10 kHz or more and 60 kHz or less. Note that the range of the frequency was selected based on the easiness of occurrence of the light emission phenomenon.
[0030]
FIGS. 2A to 2C already show waveforms when the on-duty is controlled to 50%, and FIG. 4 shows waveforms when the on-duty is controlled to 30%. 4A shows the applied voltage waveform, FIG. 4B shows the current waveform, and FIG. 4C shows the emission luminance. As shown in the figure, the luminance (the luminance indicated by the luminance waveform L3) during the period in which the drive voltage is not applied is higher than the luminance (the luminance indicated by the luminance waveform L1) during the positive voltage application period, and the luminous efficiency is further improved. It can be understood.
[0031]
The lighting circuit 5 is not limited to the circuit described in the present embodiment, but may have any other configuration as long as the external electrode 2a is fixed at 0 V and a positive rectangular wave voltage can be applied to the internal electrode 1. Alternatively, the supplied power may be a DC power supply.
[0032]
Further, as shown in FIG. 5A, the external electrode of the arc tube 3 may be composed of a plurality of electrodes which are different in distance from the internal electrode 1 in the axial direction of the arc tube 3 and are separated from each other. Good. At this time, the length (l) of the contact portion between the electrode 2b and the arc tube 3 in the circumferential direction of the arc tube 3 is set to be equal to or less than half the circumference of the arc tube 3 in order to suppress the shielding of light by the external electrodes. Is preferable (see FIG. 5B). The external electrode may be wound in a spiral shape along the tube axis direction of the arc tube 3 in addition to the one provided in a band shape and the one provided in plural at a distance.
[0033]
Further, although only one internal electrode 1 is provided at one end of the arc tube 3, the present invention is not limited to this, and the internal electrodes 1 may be provided at both ends of the arc tube 3 to apply a voltage to both ends (FIG. 5 (c)). )reference). In this case, it is preferable that the tube length of the arc tube 3 be 200 mm or more and 600 mm or less in order to make the internal discharge state the same as in the case of one internal electrode 1.
[0034]
Discharge occurs between the internal electrode 1 provided at the end of the arc tube 3 and the external electrodes 2a and 2b arranged along the entire length of the arc tube. For this reason, when the inner diameter of the arc tube 3 is small and the length of the arc tube 3 is long, the discharge needs to travel long along a narrow path in the arc tube 3, so that the amount of power supplied to the discharge lamp is adjusted. Even when the discharge gas itself absorbs ultraviolet rays, ultraviolet rays may not be emitted. In particular, if (the total length of the arc tube) / (the inner diameter of the arc tube)> 50, uniform light emission cannot be obtained over the entire length of the arc tube 3. In order to prevent this, by adding a rare gas having a higher ionization voltage as a buffer gas to the actual discharge gas, self-absorption of the discharge gas itself can be prevented, and uniform light emission can be obtained over the entire length of the arc tube 3. Specifically, when xenon gas is used as a discharge gas, it is preferable to add argon gas or neon gas as a buffer gas at a concentration equal to or less than that of the discharge gas. That is, xenon gas or krypton gas is preferably used as the discharge gas, and argon gas or neon gas is preferably used as the buffer gas.
[0035]
When the gas pressure inside the arc tube 3 is low, the amount of discharge gas inside the arc tube 3 is small. Therefore, even if the on-duty ratio is changed, an improvement in the optical output cannot be obtained. Conversely, when the gas pressure is high, the discharge gas and the buffer gas form a wall, which hinders the discharge that occurs over the entire length of the arc tube 3, so that uniform light emission cannot be obtained. Therefore, in order to obtain the effect of the present application, the range of the sealed gas pressure is preferably set to 1 kPa to 40 kPa.
[0036]
<Embodiment 2>
FIG. 6 is a diagram showing another configuration of the main part of the discharge lamp device according to the present invention. 7 is a sectional view taken along line II-II in FIG. 6, and FIG. 8 is a sectional view taken along line III-III in FIG. In the discharge lamp device L of the present embodiment, the external electrodes are not formed directly on the outer peripheral surface of the arc tube 3, but a plurality of external electrodes 2 c are arranged in parallel on a support plate 4 provided facing the arc tube 3. The external electrodes 2c arranged in parallel are fixed to the reference potential as described in the first embodiment. A discharge lamp device having a configuration in which a plurality of external electrodes 2c are arranged in parallel on such a support plate 4 and the arc tube 3 is arranged so that the extending direction of the external electrode 2c and the tube axis direction of the arc tube 3 intersect. It is disclosed in patent application 2001-285415 filed by the present applicant. By arranging a plurality of external electrodes on the support plate on which the arc tube is mounted, it is not necessary to fix the electrodes directly to the outer peripheral surface of the arc tube. Therefore, it is possible to realize a low-cost discharge lamp device that is simpler to manufacture than when the electrodes are directly fixed to the outer peripheral surface of the arc tube.
[0037]
A rare gas is sealed in the arc tube 3 shown in FIG. 6, and an internal electrode 1 made of nickel or the like is provided at one end of the arc tube 3. The support plate 4 configured to mount the arc tube 3 is formed by processing a resin member or a metal member such as aluminum. The surface of the support plate 4 is subjected to, for example, painting by silk printing or the like, or surface treatment (sanding treatment or the like) by sand blasting or the like in order to improve light reflection efficiency and diffusion efficiency. Note that the support plate 4 may have light transmission characteristics in addition to the one having light reflection characteristics. Which property is selected can be appropriately selected as needed.
[0038]
A plurality of accommodation grooves T for accommodating the arc tube 3 are formed in the support plate 4, in a direction intersecting the longitudinal direction of the accommodation groove T (that is, in a direction intersecting the axial direction of the arc tube 3). The external electrode 2 is formed of a silver paste or the like. The external electrode 2 may be formed of a conductive resin member instead of the silver paste, and may be integrally formed with the support plate 4 made of the resin member by pressure bonding. The shape of the receiving groove T is appropriately set according to the shape of the arc tube 3.
[0039]
Further, a plurality of support members 7 for supporting the arc tube 3 are provided in the accommodation groove T of the support plate 4 as shown in FIGS. The support member 7 is made of aluminum or the like, and the lower end thereof is fixed to the accommodation groove T of the support plate 4, and the upper end thereof detachably holds the arc tube 3. The arc tube 3 is held by the support member 7 and, as shown in FIG. 7, has a support plate in which a part of the external electrode 2 c arranged in parallel with the accommodation groove T and the outer peripheral surface of the arc tube 3 are in contact. 4 is locked and placed on the accommodation groove T.
[0040]
The internal electrode 1 of the arc tube 3 is connected to the lighting circuit 5 described in the first embodiment, and the driving voltage as described in the first embodiment is applied between the internal electrode 1 and the external electrode 2c of the arc tube 3. Is done. That is, the potential of the external electrode 2c is fixed to the reference potential (voltage 0 V), and a rectangular wave voltage consisting of only a positive voltage is applied to the internal electrode 1. In the discharge lamp device L configured as described above, similarly to the case of the first embodiment, a glow discharge is generated inside the arc tube 3 to shift the internal inert gas to an excited state, and change from the excited state to the ground state. The phosphors in the phosphor layer 3a are excited by ultraviolet rays emitted during the transition to emit visible light.
[0041]
Further, as shown in FIGS. 7 and 8, a flat light guide plate 6 is disposed above the discharge lamp device L such that the main surface of the light guide plate 6 and the main surface of the support plate 4 face each other. That is, a flat light guide plate 6 is provided at a position facing the support plate 4 via the arc tube 3. Thus, a backlight B such as a liquid crystal display element is formed. The visible light generated in the arc tube 3 is incident on the flat light guide plate 6 and diffused. The light guide plate 6 is made of resin or the like, and has a function of converting light generated from the arc tube 3 into a uniform surface light source. Such a backlight B is particularly effective when applied to a backlight for a liquid crystal display element from the viewpoint of small size, thin shape, and low power consumption.
[0042]
<Embodiment 3>
FIG. 9 is a diagram showing still another configuration of the main part of the discharge lamp device according to the present invention. In the second embodiment, as shown in FIGS. 7 and 8, the discharge lamp device L is a direct-type backlight arranged on the main surface side of the light guide plate 6. It is an edge-light type backlight arranged on the end face side. The backlight of this embodiment is basically the same as that of the second embodiment except that the arc tube 3 is arranged to face the end face of the light guide plate 6, and a detailed description is omitted. Note that a lighting circuit is omitted in FIG.
[0043]
<Embodiment 4>
As described in the first embodiment, the luminance can be increased by appropriately controlling the on-duty of the rectangular wave consisting of only the positive voltage applied to the internal electrode. In the present embodiment, this on-duty control will be described in detail.
[0044]
FIG. 10 is a characteristic diagram showing a change in luminance when the on-duty (T1 / T2) is changed. The horizontal axis is the on-duty (%) of a rectangular wave consisting of only the positive voltage applied to the internal electrode 1, and the vertical axis is the average luminance (cd / m) on the surface of the arc tube 3.²). The arc tube 3 used has an outer diameter of 2.6 mm, an inner diameter of 2.0 mm, a wall thickness of 0.3 mm, and a tube length of 164 mm. The noble gas is sealed in such a manner that Xe and Kr as a discharge medium are sealed at a ratio of Xe6 to Kr4, and the internal pressure is 22.2 kPa. The frequency of the applied rectangular wave is 40.0 kHz, and the voltage is 2.0 kV (this embodiment: 0 kV to +2 kV, conventional: -1 kV to +1 kV). Note that the internal electrode 1 was provided only at one end of the arc tube 3, and green was used as a phosphor. In this embodiment, LaPO4: Ce, Tb is used as the green phosphor.
[0045]
Specimens 1 to 4 were prepared under the conditions described above.
Specimen 1 is the discharge lamp device L described in the first embodiment shown in FIG. 1, in which one strip-shaped external electrode 2 having a width of 2 mm is fixed to the outer peripheral surface of the arc tube 3 along the tube axis direction. is there. Between the internal electrode 1 and the external electrode 2 of the sample 1, a rectangular wave voltage of only a positive voltage based on the external electrode 2 was applied from the lighting circuit 5 while changing the on-duty from 10% to 60%.
[0046]
Specimen 3 has the same configuration as Specimen 1, except that an alternating voltage (duty: 50%) is applied between internal electrode 1 and external electrode 2 with reference to external electrode 2. The same applies (see FIGS. 14 and 15).
[0047]
Specimen 2 is the discharge lamp device L shown in FIG. 6 described in the second embodiment, and the external electrodes 2 formed on the support plate 4 had an electrode width of 3 mm and an interval between the external electrodes 2c of 1 mm. A rectangular wave voltage consisting of only a positive voltage was applied to the sample 2 from the lighting circuit 5 while changing the on-duty from 10% to 60%.
[0048]
Specimen 4 had the same configuration as Specimen 2, but the applied voltage was an alternating voltage (duty 50%).
[0049]
In FIG. 10, the dashed two-way arrows indicate the correspondence between the specimen 1 and the specimen 3 and the correspondence between the specimen 2 and the specimen 4, respectively, and are for clarifying the improvement of the luminance characteristics. (Similarly in FIG. 11).
[0050]
Referring to FIG. 10, it can be understood that in Sample 1, when the on-duty is in the range of 15% or more and 45% or less, higher luminance can be obtained than in Sample 3 to which the alternating voltage is applied. In the sample 2, when the on-duty is in the range of 15% or more and 50% or less, higher brightness can be obtained than in the sample 4 to which the alternating voltage is applied. That is, in the discharge lamp device L according to the first to third embodiments, the on-duty is appropriately controlled so as to be within the above-described range, so that the luminance characteristic is significantly improved as compared with the conventional discharge lamp device 10L which applies an alternating voltage. Can be improved. It is considered that the luminance is increased by appropriately controlling such on-duty because excimer light emission, which is light emission in a wavelength region where the emission efficiency of the phosphor is high, increases with a change in on-duty ( (See FIGS. 3A and 3B).
[0051]
Further, in FIG. 10, when the specimen 1 and the specimen 2 are compared, the luminance of the specimen 2 is higher than that of the specimen 2 even though the rectangular wave voltage of only the positive voltage is applied to both of them. In particular, the on-duty is clearly different in the range of 30% to 50%. For example, the luminance when the on-duty is 45% is about 34 k (cd / m²), About 44 k (cd / m²) And 30% or more of the luminance is significantly improved.
[0052]
In other words, in the case where the shape of the external electrode is a belt-like shape as in the related art, the luminance is not improved by applying the rectangular wave voltage of only the positive voltage of the present invention as compared with the case of applying the alternating voltage in the related art. However, by employing a configuration in which a plurality of external electrodes are arranged apart from each other in the tube axis direction, the luminance can be greatly improved. It is needless to say that such an effect in the specimen 2 can be similarly obtained also in the arc tube 3 in FIG. When on-duty is controlled in the range of 30% to 50%, the brightness of specimen 2 is higher than that of specimen 1 because contraction discharge is likely to occur in specimen 1 due to the influence of the electrode shape. This is considered to be due to the effect of reducing the luminance associated with.
[0053]
FIG. 11 is a characteristic diagram showing a change in luminance per 1 W when the on-duty is changed as described above. The horizontal axis is the on-duty (%), and the vertical axis is the surface luminance per 1 W (cd / m).²/ W), that is, the luminous efficiency. The conditions for the specimens 1 to 4 are the same as those described above.
[0054]
Comparing Specimen 1 and Specimen 3, Specimen 1 has a higher surface brightness per 1 W in the on-duty range from slightly more than 15% to slightly less than 40%. Comparing Specimen 2 and Specimen 4, Specimen 2 has a higher surface brightness per 1 W in the on-duty range from 18% to just over 40%. That is, by controlling the on-duty within these ranges, the luminous efficiency can be improved as compared with the conventional discharge lamp device.
[0055]
From the characteristic diagrams of FIGS. 10 and 11, if the on-duty is controlled in the range from 18% to slightly more than 40%, the luminous efficiency can be improved as well as the luminance, which cannot be obtained in the conventional discharge lamp device. High luminance characteristics and luminous efficiency can be obtained.
[0056]
Next, the case where a rectangular wave voltage of only a negative voltage is applied between the external electrode and the internal electrode will be examined. For this reason, a new specimen 5 was prepared for comparison. The sample 5 is the discharge lamp device L having the configuration shown in FIG. 6 described in the second embodiment, in which the polarity of the voltage applied from the lighting circuit 5 is reversed, and a rectangular wave voltage of only a negative voltage is applied. Things. That is, the sample 5 measured luminance and luminous efficiency by applying a rectangular wave voltage of only a negative voltage to the internal electrode 1 with the external electrode 2c as a reference voltage (0 V) and appropriately changing the on-duty.
[0057]
FIG. 12 is a characteristic diagram for comparing a difference in luminance between a case where a rectangular wave voltage of only a positive voltage is applied between an external electrode and an internal electrode and a case where a rectangular wave voltage of only a negative voltage is applied. The horizontal axis represents the on-duty (%), and the vertical axis represents the average luminance (cd / m) of the surface of the arc tube 3.²) Are shown. FIG. 13 is a characteristic diagram showing a change in luminance per 1 W in that case. The horizontal axis is the on-duty (%), and the vertical axis is the surface luminance per 1 W (cd / m).²/ W). Note that, with respect to the sample 5, the on-duty (%) is defined assuming that a period during which a rectangular wave voltage of only a negative voltage is applied is T1 and a cycle is T2. The characteristics were measured for specimens 2, 4, and 5.
[0058]
In FIG. 12, when the specimen 2 and the specimen 5 are compared, the on-duty of the specimen 2 that applies the rectangular wave voltage of only the positive voltage is 10% to 50% compared to the specimen 5 that applies the rectangular wave voltage of only the negative voltage. Up to the range, the luminance characteristics are excellent. In other words, applying a rectangular wave voltage consisting of only a positive voltage is more effective in improving brightness than applying a rectangular wave voltage consisting of only a negative voltage.
[0059]
In FIG. 13, a comparison between the specimen 2 and the specimen 5 shows that the on-duty of the specimen 2 that applies the rectangular wave voltage of only the positive voltage is 10% to 50% as compared with the specimen 5 that applies the rectangular wave voltage of only the negative voltage. Luminous efficiency is excellent in the range up to weak. That is, applying a rectangular wave voltage of only a positive voltage is more effective in improving luminous efficiency than applying a rectangular wave voltage of only a negative voltage.
[0060]
As described above, applying a rectangular wave voltage of only a positive voltage between an external electrode and an internal electrode is more effective in improving luminance and luminous efficiency than applying a rectangular wave voltage of only a negative voltage. There is.
[0061]
In this embodiment, the evaluation result is shown for a single green color, but the phosphor used in the arc tube is LaPO.₄: It is not limited to Ce and Tb. For example, for a blue phosphor, BaMgAl_xO_y: Eu etc. (x and y are optional), if green, LaPO₄: Ce, Tb or Zn₂SiO₄: Mn or BaMg₂Al_{1 4}O₂₄: Y if Eu, Mn, etc. is red₂O₃: Eu, (Y, Gd) BO₃: Eu, YPVO₄: Eu, YVO₄: A commonly used phosphor such as a phosphor for a three-wavelength emission type fluorescent lamp such as Eu, a phosphor for a plasma display, and a halophosphate phosphor for white light emission can be appropriately selected and used. By increasing the excimer emission ratio of the discharge gas, generally, the quantum efficiency of the phosphor is increased, and the light output can be increased.
[0062]
【The invention's effect】
According to the present invention, in the backlight and the backlight for a liquid crystal display element, the second electrode, which is the external electrode, is set to the reference potential (applied voltage: 0 V), and the first electrode, which is the internal electrode, is rectangular with only a positive voltage. Since a wave voltage is applied, sufficient luminance can be obtained even when a falling current flows when the positive voltage falls, and luminous efficiency can be improved.
[0063]
Further, according to the present invention, since the support plate for the arc tube is provided, and a plurality of the second electrodes are arranged on the support plate, the formation of the external electrode is facilitated, the luminance characteristics and the luminous efficiency are improved, and the production of the arc tube is improved. Cost reduction and simplification can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of a schematic configuration of a discharge lamp device according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an applied voltage waveform, a current waveform, and luminance of an arc tube in the discharge lamp device of the present invention.
3A is a diagram showing an emission spectrum of a rare gas (xenon gas), and FIG. 3B is a diagram showing an excitation spectrum of a phosphor.
FIG. 4 is a diagram showing an applied voltage waveform, a current waveform, and the luminance of an arc tube when the on-duty is appropriately controlled in the discharge lamp device of the present invention.
5A is a block diagram showing another example of the configuration of the discharge lamp device according to the first embodiment of the present invention, FIG. 5B is a cross-sectional view of an arc tube, and FIG. 5C shows light emission provided with internal electrodes at both ends. Tube illustration
FIG. 6 is a diagram showing a configuration example of a discharge lamp device according to a second embodiment of the present invention.
7 is a sectional view of the discharge lamp device (backlight) in FIG. 6 taken along line II-II.
8 is a cross-sectional view of the discharge lamp device (backlight) in FIG. 6 taken along line III-III.
FIG. 9 is a diagram showing a configuration example of a main part of a discharge lamp device according to a third embodiment of the present invention.
FIG. 10 is a characteristic diagram showing a change in luminance when the on-duty is changed in the fourth embodiment.
FIG. 11 is a characteristic diagram showing a change in luminance per 1 W when on-duty is changed in the fourth embodiment.
FIG. 12 is a characteristic diagram comparing luminance changes when a positive / negative rectangular wave voltage is applied in the fourth embodiment.
FIG. 13 is a characteristic diagram showing a change in luminance per 1 W when a positive / negative rectangular wave voltage is applied in the fourth embodiment.
FIG. 14 schematically shows a conventional discharge lamp device.
FIG. 15 is a diagram showing an applied voltage waveform, a current waveform, and the luminance of an arc tube in a conventional discharge lamp device.
[Explanation of symbols]
1 internal electrode
2a, 2b, 2c External electrode
3 arc tube
5 lighting circuit
P AC power supply
C rectifier circuit
SC smoothing circuit
TC booster circuit
S switching circuit
G ground point
4 support plate
T accommodation groove
L discharge lamp device
6 Light guide plate
B Backlight
7 Supporting member

Claims (11)

A discharge lamp device for driving an arc tube in which a rare gas is sealed, a first electrode is provided inside, and a second electrode is provided outside,
A lighting circuit for applying a voltage between the first electrode and the second electrode;
The discharge lamp device, wherein the lighting circuit applies a positive rectangular wave voltage to the first electrode using a potential of the second electrode as a reference potential. 2. The discharge lamp device according to claim 1, wherein the second electrode includes a plurality of electrodes spaced apart in a tube axis direction of the arc tube. 3. A discharge lamp device for driving an arc tube in which a rare gas is sealed and a first electrode is provided therein,
A plurality of second electrodes arranged in parallel, a support plate for supporting the arc tube in proximity to the arc tube,
A lighting circuit for applying a voltage between the first electrode and the second electrode,
The discharge lamp device, wherein the lighting circuit applies a positive rectangular wave voltage to the first electrode using a potential of the second electrode as a reference potential. The discharge lamp device according to any one of claims 1 to 3, wherein the rare gas is xenon gas or krypton gas. The discharge lamp device according to any one of claims 1 to 3, wherein the rectangular wave voltage has an on-duty of 15% or more and 50% or less. The discharge lamp device according to claim 5, wherein the frequency of the rectangular wave voltage is 10 kHz or more and 60 kHz or less. The discharge lamp device according to claim 5, wherein the first electrode is provided at one end of an arc tube, and a length of the arc tube is 100 mm or more and 300 mm or less. The discharge lamp device according to claim 5, wherein the first electrodes are provided at both ends of the arc tube, and a length of the arc tube is 200 mm or more and 600 mm or less. The discharge lamp device according to claim 5, wherein the arc tube has a cylindrical shape, an inner diameter of 1 mm or more and 10 mm or less, and a thickness of 0.2 mm or more and 0.5 mm or less. A backlight comprising at least one arc tube and the discharge lamp device according to any one of claims 1 to 9. 11. The backlight according to claim 10, further comprising a light guide plate to be arranged on a back surface of the liquid crystal display element, wherein the arc tube is arranged to face the light guide plate.

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