JP3685073B2 - Flat light source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a flat light source such as a discharge device that emits light in a flat form, for example, a display element that requires a backlight such as a liquid crystal panel, for example, information video equipment such as a TV, a game machine, a car navigation system, a word processor, etc. The present invention relates to a flat light source, a lighting device using a flat light source, and a liquid crystal display device in an OA device or a display system incorporating a light source.
[0002]
[Prior art]
Liquid crystal panels are thin and light and have low power consumption, so they are widely used as various information video displays such as personal computers and televisions. A backlight that supplies light is required. The backlight that is usually used is mainly a combination of a small-diameter fluorescent lamp and an acrylic resin light guide, but a flat discharge lamp is also used.
[0003]
FIG. 5 is a cross-sectional view of a conventional flat light source described in, for example, JP-A-9-115483. As shown in the figure, a translucent front plate 2 made of soda glass or the like and a back plate 3 made of soda glass or ceramic are integrally hermetically sealed with, for example, low-melting glass (not shown), An airtight container 1 having a flat discharge space 8 is configured. A pair of discharge electrodes 4, 5 parallel to each other are provided on the inner surface of the front plate 2 serving as a light emitting surface, and the surfaces of the discharge electrodes 4, 5 are covered with a dielectric layer 6. A phosphor 7 is applied to the inner surfaces of the front plate 2 and the insulating substrate 3, and a mixed gas of rare gas such as xenon-argon or xenon-argon-neon or mercury is applied to the discharge space 8 in the sealed container 1. And a discharge gas such as a rare gas is enclosed.
[0004]
The flat light source according to the present configuration generates a discharge in the discharge space 8 by applying a high-frequency voltage (for example, a voltage pulse having a rest period) between the discharge electrodes 4 and 5, and phosphors by the ultraviolet rays generated by the discharge 7 is excited to emit light, and light is emitted to the outside through the front plate 2.
[0005]
[Problems to be solved by the invention]
The flat light source excites phosphors with ultraviolet light from xenon, but has a problem of low brightness and efficiency. In order to improve the efficiency, for example, when a voltage pulse having a frequency of 20 kHz and a pulse width of about 1 μs is applied and discharged, the efficiency is improved, but the luminance is not so high. When the voltage is increased to increase the brightness, the discharge contracts or becomes non-uniform and safety becomes a problem. In addition, there is a problem that the luminance cannot be increased while maintaining high efficiency, for example, high voltage circuit components are required and the cost is increased.
When driven by a rectangular wave, the brightness can be increased. However, the conventional flat light source described above has a problem that the discharge contracts and the flat light emission does not occur or the uniformity is deteriorated and cannot be used as a backlight of a liquid crystal display device. .
[0006]
An object of the present invention is to solve the above-described problems, and is to provide a flat light source having a simple configuration, high luminance, high efficiency, and good uniformity.
[0007]
[Means for Solving the Problems]
To achieve the above object, in the present invention, a light-transmitting front plate and an insulating substrate are combined to form a sealed container having a flat discharge space, and at least a pair of discharges are formed on the inner surface of the front plate. In a flat light source in which an electrode is provided, a dielectric layer is provided to cover the surface of the discharge electrode, and a discharge gas is sealed inside the sealed container, the width of the discharge electrode is set to 0.2 mm or more and 1.8 mm or less . Further, as the discharge gas, xenon or a gas in which xenon and other rare gas are mixed is used. Further, mercury and a rare gas are enclosed as the discharge gas. A phosphor is provided on the inner surface of the sealed container. Further, a rectangular wave is applied to the discharge electrode for discharge.
[0008]
In addition, the discharge electrode is provided over substantially the entire length of the side of the discharge space, or the discharge electrode is divided into a plurality of parts.
[0009]
A protective film is provided on the surface of the dielectric layer.
[0010]
Moreover, it is comprised in an illuminating device so that it may illuminate using said flat type light source.
[0011]
In the liquid crystal display device, the flat light source is used as a backlight.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a flat light source according to the present invention. As shown in the figure, a translucent front plate 2, a back plate 3, and a side plate 9 made of, for example, soda glass are integrally hermetically sealed with, for example, low melting point glass (not shown), so that a flat sealed container is formed. 1 is configured. For the back plate 3, for example, a box-shaped container integrated with the side plate 9 may be used. A pair of parallel discharge electrodes 4 and 5 having a width Wmm are provided on the inner surface of the front plate 2, and the surfaces of the discharge electrodes 4 and 5 are covered with a dielectric layer 6 provided by a thick film printing method or the like. Yes. A phosphor 7 is applied to the inner surfaces of the front plate 2, the rear plate 3, and the side plate 9, and a mixed gas of xenon-argon-neon is sealed in the discharge space 8 in the sealed container 1 as a discharge gas. The size of the light emitting surface is, for example, 52 mm to 40 mm when used for a backlight for a 2.5 inch liquid crystal. At this time, the distance between the electrodes is about 54 mm, and the height of the discharge space 8 is 1.8 mm. Further, when used for a backlight for a 5-inch liquid crystal, it is 105 mm to 75 mm. At this time, the distance between the electrodes is about 80 mm and the height of the discharge space 8 is 2.4 mm.
[0013]
In the driving method of the flat light source according to this embodiment, a rectangular wave is applied to the discharge electrodes 4 and 5 to cause discharge.
[0014]
FIG. 2 is a diagram showing an example of a rectangular wave voltage waveform. For example, a rectangular wave or a substantially rectangular wave voltage 11 having a voltage of Vs and −Vs around 0 V is applied to the discharge electrode 4, and the discharge electrode 5. Are discharged by applying a voltage 12 of a rectangular wave or a substantially rectangular wave having a polarity opposite to that of 11 at the same frequency.
In this way, a discharge is generated in the discharge space 8, the phosphor 7 is excited by the ultraviolet rays generated by the discharge and emits light, and the light is emitted outside through the front plate 10.
When the drive voltage waveform described above is used, a voltage twice as high as Vs is applied between the discharge electrodes 4 and 5, so that the output voltage per circuit is low and the circuit configuration is simplified. As in the above-described embodiment, a rectangular wave voltage may be applied to both electrodes, or may be applied to one electrode and discharged.
FIG. 3 is a diagram showing another driving waveform. For example, −Vh is applied to the electrode 4.
A voltage 11 having a voltage pulse of 5 is applied, and the other electrode 5 is discharged by applying a voltage 12 having the same voltage pulse as 11 and a voltage pulse -Vh having a half-cycle phase shift. If the pulse width W1 and the rest period W2 are set to the same time width, the voltage waveform including the voltage 11 and the voltage 12 becomes a rectangular wave, and the rectangular wave is driven. The frequency can be used from 10 kHz to 100 kHz.
Since the above-described flat light source is a capacitive load, the charge moves with application of voltage and accumulates in the dielectric layer 6 on the electrode to become wall charges. When the external electric field and the electric field due to the wall charge become equal, the movement of the wall charge stops and the current also stops. As described above, since the discharge of the flat light source according to the present configuration is dominated by the wall charges, the conventional flat light source has a large amount of the wall charges when driven by a rectangular wave, causing discharge contraction.
FIG. 4 is a characteristic diagram showing the relationship between the width W of the discharge electrodes 4 and 5 and the stable operating frequency region when a rectangular wave is applied to a flat light source for discharge.
As shown in the figure, as the width W of the discharge electrodes 4 and 5 is reduced, the discharge can be performed without contracting the discharge with a high-frequency rectangular wave. In order to control the wall charges, the electrode width W and the driving frequency may be selected as a stable operation region, and a flat light source with high efficiency and high brightness can be obtained in the stable operation region of FIG.
In rectangular wave lighting, when the width W of the discharge electrode is 4 mm or more, the discharge contracts regardless of the frequency and flat light emission does not occur. In addition, from about 4 mm to about 2 mm, the light can be lit with a rectangular wave, but the lit frequency is low and is in the audible frequency range. In this frequency range, a sound can be heard when lit. For example, if a flat light source is used for the backlight of a portable device, an abnormal sound can be heard in this frequency range, so that it cannot be used. The electrode width W is 1.8
When it is less than mm, the lighting frequency is about 17 kHz and exceeds the audible frequency range, so there is no abnormal noise and it can be used.
When the electrode width W is narrower than 0.2 mm, the wall charge accumulated in the dielectric layer becomes too small, and a high voltage needs to be applied in order to obtain high luminance. In addition, when the electrode is formed by, for example, a thick film printing method or the like, if the line width is thinner than 0.2 mm, disconnection or line width unevenness may occur. For these reasons, the width W of the discharge electrode is a practical width of 0.2 mm or more.
From the above results, if the width W of the discharge electrode is between 0.2 mm and 1.8 mm, a flat light source that can be driven by a rectangular wave can be obtained.
[0015]
In the above-described embodiment, an example of a mixed gas of rare gas as a discharge gas has been described. However, similar results can be obtained even when mercury is sealed.
[0016]
The length of the discharge electrode is substantially the same as the total length of the side of the discharge space 8 in the above embodiment, but is not limited to this, and may be slightly shorter, and may be formed longer than the side of the discharge space to the sealed portion. May be. In addition, the discharge electrode becomes longer as the light emitting surface becomes larger, but if the discharge electrode becomes too long, the discharge current increases and the current capacity of the drive circuit increases. If the current capacity of the drive circuit increases, problems such as heat dissipation and high costs will arise. In this case, if the discharge electrode is divided into an appropriate number, the current per electrode will decrease, so the circuit will be reduced. Can be small.
In addition, the discharge electrodes 4 and 5 may use a transparent conductive film such as an ITO film or a nesa film. Further, by covering the surface of the dielectric layer 6 with a protective layer (not shown) such as MgO, the operating voltage can be reduced and the sputtering can be reduced, and a long-life flat plate light source can be obtained.
[0017]
As described above in detail, the flat light source according to the present invention is characterized in that it can be lit with a rectangular wave, maintains high luminance, high luminous efficiency, and stable planar light emission. Further, when the flat light source according to the present invention is used as, for example, a light source for a backlight of a liquid crystal display device, a backlight having a high luminance and a long life can be obtained.
[0018]
【The invention's effect】
According to the present invention, even if xenon or a mixed gas of xenon and other rare gas is used as the sealing gas, it can be lit with a rectangular wave, has high brightness, high luminous efficiency, stable discharge, and good uniformity in flat discharge. A light source is obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a flat light source according to the present invention.
FIG. 2 is a drive voltage waveform of a flat light source.
FIG. 3 is another drive voltage waveform of the flat light source.
FIG. 4 is a characteristic diagram showing the relationship between electrode width and frequency.
FIG. 5 is a cross-sectional perspective view showing a conventional flat light source.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Sealed container 2 ... Front plate 3 ... Back plate 9 ... Side plate 4, 5 ... Discharge electrode 11, 12 ... Drive voltage waveform 6 ... Dielectric layer 7 ... Phosphor 8 ... Discharge space .

Claims (9)

A light-transmitting front plate and an insulating substrate are combined to form a sealed container having a flat discharge space, a pair of discharge electrodes are provided on the inner surface of the front plate, and the surface of the discharge electrode is covered with a dielectric. In a flat light source in which a discharge gas is sealed inside the sealed container , a rectangular wave is applied to the discharge electrode for discharge , and the width of the discharge electrode is 0.2 mm to 1.8 m A flat light source characterized by that. The flat light source according to claim 1, wherein xenon or a gas obtained by mixing xenon and another rare gas is used as the discharge gas. The flat light source according to claim 1, wherein mercury and a rare gas are enclosed as the discharge gas. The flat light source according to any one of claims 1 to 3, wherein a phosphor is provided on an inner surface of the sealed container. The flat plate light source according to any one of claims 1 to 4 , wherein the discharge electrode is provided over substantially the entire length of the side of the discharge space. Plate type light source according to any one of claims 1 to 5, characterized in that a transparent conductive film of ITO film or nesa film as the discharge electrode. The flat light source according to any one of claims 1 to 6 , wherein a protective film is provided on a surface of the dielectric layer. An illumination device configured to illuminate using the flat light source according to any one of claims 1 to 7 . The liquid crystal display device characterized by using a plate type light source according as a backlight of claims 1 to claim 7.

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