JP2009134992A - Backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve homogenization of a light-emitting face without increasing thickness of a cabinet since difference in brightnesses in the normal direction at a position directly above a lamp and between the lamps becomes smaller by forming a secondary light source between the lamps. <P>SOLUTION: In a backlight device having a plurality of fluorescent lamps 1 supported on a reflecting sheet 3 and arranged parallel, a diffusion plate 4 arranged and installed above the fluorescent lamps, and a reflecting member 5 arranged and installed parallel to a tubular axis at the center position between the neighboring fluorescent lamps 1, 1 on the reflection sheet 3, the reflection member 5 has a triangular cylindrical shape having a hollow inside, and a plurality of opening parts 6, 7 periodically arranged with a prescribed pitch in the tubular axis direction are installed by shifting them by a half pitch in the respective sidewalls 14, 15 of a reflecting member 5 opposed to respective neighboring fluorescent lamps 1, 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a direct backlight device used as a back light source of a liquid crystal display device.

  In general, a direct type backlight device used as a back light source of a liquid crystal display device has a fluorescent lamp 101 called a cold cathode tube having a lamp diameter of about 3 mm to 4 mm as shown in FIG. A plurality of plates 103 are arranged side by side in a housing 102 provided with a plate 103. Actually, a diffusion plate (not shown), a lens sheet, or the like is disposed in the upper surface opening of the housing 102. In this configuration of the backlight device, the light flux increases as the number of fluorescent lamps 101 increases, and a uniform light-emitting surface can be obtained as the pitch between adjacent lamps decreases and the thickness of the housing 102 increases. For example, in the case of the 20 type class, the number of lamps is about 10, the pitch between the lamps is about 25 mm, and the thickness of the housing is about 20 mm.

  As a problem of the backlight device, there is a problem that the number of fluorescent lamps 101 used is large. In recent years, it has been possible to reduce the number of lamps used by increasing the luminous efficiency of the fluorescent lamp 101, improving the transmittance of the liquid crystal panel, and increasing the current of the fluorescent lamp 101. Then, since the pitch between the lamps becomes wide, there arises a problem that the thickness of the housing 102 must be increased in order to obtain a uniform light emitting surface.

  Therefore, in Patent Document 1 and Patent Document 2, as shown in FIG. 15, a triangular prism-shaped reflecting member 105 parallel to the tube axis of the fluorescent lamp 101 is provided at the center position between the lamps on the bottom surface of the housing 102. It is disclosed that light emission from the fluorescent lamp 101 is diffusely reflected on the side surface of the fluorescent lamp 101 so as to make the light emitting surface uniform without increasing the thickness of the housing 102 even when the pitch between the lamps is widened. ing.

  Here, since the normal direction (upward direction in FIG. 15) of the light emitting surface of the backlight device is the viewing direction as the display device, it is desirable that the luminance in this direction be relatively high. However, when the reflecting member 105 has a high diffuse reflectance, the light emission luminance of the fluorescent lamp is almost uniform in all directions, whereas the light other than the light that is regularly reflected by the reflecting member 105 as shown in FIG. Since there is also light that is diffusely reflected, the luminance in the normal direction at the center position between the lamps is much lower than immediately above the lamp. When this is seen over the entire light emitting surface of the backlight device, as shown in FIG. 17, the luminance in the normal direction is in a relationship between peaks and valleys between the lamp directly above and the center position between the lamps. It will be big.

  As a solution to this, it is conceivable that the surface of the reflecting member 105 is mirror-finished to create a mirror image of the fluorescent lamp 101 on the side surface of the reflecting member 105 as a secondary light source, thereby enhancing the luminance in the normal direction of the valley portion. . However, on the contrary, since the luminance in the perspective direction becomes extremely small, there arises a problem that the viewing angle of the liquid crystal display device becomes narrow.

  Furthermore, in recent years, in order to reduce the number of fluorescent lamps, a hot cathode tube having high luminous efficiency and a large luminous flux may be used. In this case, although the number of lamps can be drastically reduced (for example, in the case of the 20 type, a required light flux can be secured with 2 to 3 lamps), the pitch between the lamps is increased correspondingly, and the reflecting member 105 is relatively. As a result, the above problem becomes significant as shown in FIG.

  As a solution to this, as shown in FIG. 18B, it is conceivable to increase the light receiving area by gradually reducing the inclination angle of the side surface of the reflecting member 105. However, when the pitch between the lamps is extremely wide, it is necessary to make the tilt angle fairly gentle, and the traveling direction of the chief ray itself deviates from the normal direction of the light emitting surface of the backlight device, which is counterproductive. It can be.

The present invention has been made in view of the above-described conventional problems, and by creating a secondary light source between the lamps, the difference in luminance in the normal direction between the lamp and the position between the lamps is reduced, and the thickness of the housing is reduced. An object is to realize uniform light emitting surface without increasing.
JP 2002-1825479 A JP 2002-82624 A

  In order to achieve the above object, the present invention provides a tubular fluorescent lamp having at least two straight tube portions that are supported on a reflecting plate and arranged in parallel, a diffuser plate disposed above the fluorescent lamp, In a backlight device having a reflecting member disposed in parallel to the tube axis at a central position between adjacent straight pipe portions on a reflecting plate, the reflecting member has a triangular cylindrical shape having a cavity inside In addition, a plurality of openings periodically arranged at a predetermined pitch in the tube axis direction are provided on each side wall of the reflecting member facing each of the adjacent straight tube portions with a half pitch shift.

  According to this configuration, a part of the emitted light from the fluorescent lamp enters the inside of the reflecting member through the opening and is diffusely reflected on the inner surfaces of the side wall and the bottom wall of the reflecting member. The inner surface of the wall itself becomes a secondary light source, and the secondary light source can be seen from above through the opening.

  The opening may be formed of an assembly of a plurality of minute holes. In this case, since the emitted light from the fluorescent lamp is shuffled when passing through the minute hole in the opening, it is possible to suppress luminance spots and color spots generated in the fluorescent lamp itself, and more A uniform light emitting surface can be provided.

  According to the present invention, by creating a secondary light source between the lamps, the difference in luminance in the normal direction between the lamp and the position between the lamps is reduced, and the light emitting surface is made uniform without increasing the thickness of the housing. It becomes possible.

  The best mode for carrying out the present invention will be described with reference to the drawings. In the following embodiments, a backlight unit that illuminates a liquid crystal display having a size of about 20 inches will be described as an example.

<First Embodiment>
FIG. 1 is a top view (a) in which the diffusion plate of the backlight unit according to the first embodiment is omitted, and a side sectional view (b) of the backlight unit. FIG. 2 is a perspective view showing a reflecting plate and a reflecting member of the backlight unit.

  In the figure, 1 is a fluorescent lamp, 2 is a casing (substrate) made of sheet metal such as long rectangular box-shaped aluminum, a reflection sheet 3 is attached to the inner surface of the casing 2, and a diffusion plate 4 is disposed on the upper part. It is arranged. The fluorescent lamp 1 is turned on by a lighting circuit device (not shown), and this lighting circuit device may be a general one. For example, as shown in FIG. 13, an inverter circuit (a series LC using a half-bridge switching circuit) is used. (Oscillator circuit). The reflective sheet 3 attached to the housing 2 functions as a reflector. However, when the housing 2 is resin-molded with polycarbonate having a high reflectance, the housing 2 itself is attached to the reflector. Therefore, the reflection sheet 3 can be omitted.

  The fluorescent lamp 1 is a tubular light source (for example, a fluorescent lamp). The smaller the number of light sources used, the easier it is to obtain the effect of a pseudo light source, which will be described later. In consideration of the balance between thickness and total luminous flux, a hot cathode fluorescent lamp with a tube diameter of 15.5 mm is used.

  The fluorescent lamp 1 is supported by a lamp fixing pin (not shown) fixed to the bottom surface of the housing 2. With such a support structure, two fluorescent lamps 1 are arranged in parallel in the housing 2 at a predetermined interval.

  The fluorescent lamp 1 is composed of a cylindrical glass tube having a thickness of about 0.5 mm, and contains an electron-emitting substance (an oxide of an alkaline earth metal such as Ba, Ca, Sr or a tungstic acid of an alkaline earth metal). It has a coiled filament electrode (constructed with W or the like) coated with a salt or the like, and is filled with mercury or a rare gas (Ar or the like). Further, a three-wavelength phosphor film in which phosphors having RGB light emitting regions are mixed is formed in a strip shape along the tube axis with a predetermined film thickness on the entire inner wall of the fluorescent lamp 1.

  On the bottom surface of the housing 2, a triangular cylindrical reflecting member 5 having an isosceles cross section and a hollow inside is provided at the center position between the two lamps 1, 1 on the tube axis of the fluorescent lamp. It is laid in parallel. Since the reflecting member 5 is made of polycarbonate or the like having a high reflectance like the reflecting sheet 3, the left and right side walls 14 and 15 of the reflecting member 5 and the inner surfaces 14a, 15a and 16a of the bottom wall 16 are also highly reflective. It becomes. A plurality of rectangular openings 6 and 7 are periodically arranged in the tube axis direction of the fluorescent lamp 1 on the left and right side walls 14 and 15 of the reflecting member 5 facing the fluorescent lamp 1. The openings 6 and 7 located at the closest positions are shifted by a half pitch in the tube axis direction so as not to overlap each other in a direction perpendicular to the tube axis of the fluorescent lamp 1.

  As described above, the reflecting member 5 may be formed by disposing a resin molded product such as polycarbonate having a high reflectance on the bottom surface of the casing 2 made of sheet metal such as aluminum. When the resin itself is molded with polycarbonate, the reflecting member 5 may be integrally formed simultaneously with the resin molding of the housing 2.

  The diffusion plate 4 is provided for diffusing the direct light from the fluorescent lamp 1 and the reflected light from the reflection sheet 3 to create a uniform surface light source. The material of the diffusion plate 4 is preferably a polycarbonate resin plate having a thickness of about 2 mm filled with a diffusion material. Further, in order to increase the luminance uniformity of the light emitting surface, a diffusion sheet may be stacked on the upper surface of the diffusion plate 4, and in order to increase the luminance of the light emitting surface, a lens sheet or a reflective polarizing plate may be used. 4 may be stacked on the upper surface.

  Further, when the image (luminance spot) 8 of the fluorescent lamp 1 appearing on the light emitting surface cannot be erased even if the diffusing plate 4 is used, as shown in FIGS. You may affix the dot-shaped light absorption material 9 which has the same occupation area in the range which opposes the fluorescent lamp 1 in a back surface (light-incidence surface). In this case, the dot diameter φ of the light absorbing material 9 is about 1 mm. A light reflecting material can be used instead of the light absorbing material. In addition, since the luminance of the light emitting surface has a distribution that attenuates toward the target on the tube axis of the fluorescent lamp 1 with the peak immediately above the fluorescent lamp 1 as a peak, the range facing the fluorescent lamp 1 on the back surface (light incident surface) of the diffusion plate 4 The dot-shaped light absorbing material 10 may be formed in a gradation so that the occupied area becomes smaller as the distance from the top of the fluorescent lamp 1 increases. Moreover, as shown in FIG. 4, even if it uses the film (light curtain) 11 which gave the light absorption dot (or light reflection dot) with the pattern similar to the light reflection materials 9 and 10 shown to Fig.3 (a). good.

  In the backlight device having the above-described configuration, when the fluorescent lamp 1 is turned on via the lighting circuit device, the phosphor film is excited by the discharge in the glass tube to emit and emit light. Then, the light is transmitted through the phosphor film and diffused to go out of the lamp, and is directly reflected on the diffusion plate 4 or reflected on the surface of the reflection sheet 3 or the outer surfaces of the side walls 14 and 15 of the reflection member 5 to become reflected light. Irradiated. The direct light and reflected light at this time are the same as before.

  Next, the path of the radiated light entering the cavity from the opening 6 or 7 of the reflecting member 5 will be described with reference to FIG. For simplicity, FIG. 5 focuses on light (chief ray) radiated from the fluorescent lamp 1 in the horizontal right direction as shown in FIG. Only the case of regular reflection inside the cavity will be described.

  The radiated light that has entered the cavity from the opening 6 of the left wall 14 of the reflecting member 5 is, as shown in FIG. 5B, an inner surface 15a (referred to as a “second reflecting surface”) of the facing right wall 15. It is reflected by. At this time, if the inclination angle of the left and right side walls 14 and 15 is θ degrees, the incident angle and the reflection angle to the second reflecting surface 15a are (90−θ) degrees. Next, this light beam is reflected by the inner surface 16a (referred to as "third reflecting surface") of the bottom wall 16 of the reflecting member 5, as shown in FIG. The incident angle and the reflection angle are (90−2θ) degrees, which is smaller by θ degrees than the second reflecting surface 15a. If the inclination angle θ exceeds 45 degrees, the sign is reversed (minus), and the traveling direction of the light is reversed. If the traveling direction of the light does not reverse, as shown in the figure, the light reaches the second reflecting surface 15a again, and the incident angle and the reflecting angle at this time are further reduced by θ degrees. When reversed, the traveling direction of the light is reversed, and the light travels in the original direction (that is, the direction of the opening 6) as illustrated. Further, this light is reflected by the inner surface 14 a (referred to as “first reflecting surface”) of the left side wall 14 of the reflecting member 5, travels to the third reflecting surface 16 a, and enters the third reflecting surface 16 a. Depending on the corner, it goes again to the second reflecting surface 15a.

  In the above description, the chief ray is described. However, since the reflecting member 5 is made of a material having a high diffuse reflectance, the sign inversion phenomenon as described above is caused by light having various emission angles each time reflection occurs. Occurs in. Therefore, the light once incident on the opening 6 propagates in various traveling directions inside the cavity of the reflecting member 5 and repeats diffuse reflection. Since the diffuse reflectance of the reflecting member 5 is about 98%, almost no light is absorbed, and the inner surfaces of the left and right side walls and the bottom wall of the reflecting member 5 become secondary light sources. 7, the third reflecting surface 16a can be seen through from above as a secondary light source. This secondary light source is formed in a straight tube like the fluorescent lamp 1 which is an actual light source (primary light source).

  In order to use the openings 6 and 7 as a secondary light source as described above, it is desirable that the rectangular openings 6 and 7 be as large as possible. However, in order to realize the phenomenon shown in FIG. Since light entering the cavity from the opening 6 of the left wall 14 of the member 5 does not pass through the right wall 15, the left wall 14 and the right wall 15 are perpendicular to the tube axis of the fluorescent lamp 1. The openings 6 and 7 should not overlap.

  That is, as shown in FIG. 1, the positions of the openings 6 and 7 are arranged so that they appear alternately on the left and right side walls 14 and 15 (see FIG. 1) facing the fluorescent lamp 1 of the reflecting member 5 alternately. It is necessary to shift the pitch by half a pitch in the direction of one tube axis. Here, the sizes and pitches of the openings 6 and 7 are all the same, and the central axes of the openings 6 and 7 must be parallel to the tube axis of the fluorescent lamp 1.

  Specifically, as shown in FIG. 6, the side (short side) X of the openings 6 and 7 in the direction perpendicular to the tube axis of the fluorescent lamp 1 is seen through the bottom wall 15 of the reflecting member 5. In order to use (see FIG. 1) as a secondary light source, it is desirable to set the diameter of the fluorescent lamp 1 to be approximately the same. Further, the side (long side) Y in the tube axis direction of the fluorescent lamp 1 of the openings 6 and 7 is desirably set to 5 mm or less. The reason is that the long side Y coincides with the distance between the openings 6 and 6 (or between 7 and 7), and if it is set to 5 mm or more, the contrast becomes conspicuous and it becomes difficult to form a straight tubular secondary light source, This is because the thickness of the housing 2 is increased and the backlight device cannot be thinned in order to equalize this with the diffusion plate 4 or the like disposed above the reflecting member 5.

  Further, it is desirable that the height of the vertex of the reflecting member 5 is substantially the same as that of the fluorescent lamp 1 as shown in FIG. If it is higher than the fluorescent lamp 1, its apex may be recognized as a ridge line even if the diffusion plate 4, diffusion sheet or the like is placed above it. This is because the amount of radiated light from the entering fluorescent lamp 1 is reduced, and the effect of the secondary light source due to the multiple reflection is reduced.

  Further, as shown in FIG. 7, the heights of the opening portions 6 and 7 on the left and right side walls 14 and 15 of the reflecting member 5 include the bisector in the height direction of the fluorescent lamp 1 and the heights of the openings 6 and 7. It is desirable to set the position where the bisectors in the height direction coincide. Thereby, since the light receiving angle of the radiated light from the fluorescent lamp 1 can be maximized, more light can enter the cavity of the reflecting member 5 through the openings 6 and 7. The inclination angle θ of the left and right side walls 14 and 15 of the reflecting member 5 is determined depending on the lamp diameter of the fluorescent lamp 1 to be used and the size of the pitch between the lamps.

  Luminance in the normal direction (AA ′ line and B shown in FIG. 1) using the experimental apparatus of the backlight unit of the present invention having various parameters shown in FIGS. FIG. 9 shows the result (solid line) of the measurement of the (B ′ line synthesis). The driving current of the fluorescent lamp 1 is a sine wave having an effective value of 200 mA and a frequency of 50 kHz. For comparison, the results are also shown for a case where no reflecting member is provided between the lamps (dotted line) and a case where a reflecting member having no opening is provided at the center position between the lamps (dashed line).

When no reflecting member is provided between the lamps, the normal direction luminance is about 20000 cd / m ² immediately above the fluorescent lamp 1 as shown by a dotted line in FIG. There is only about cd / m ² , and the lack of brightness is remarkable. Further, when a reflecting member having no opening is provided at the central position between the lamps, the normal direction luminance at the central position between the lamps is about 4000 cd / m ^{2 as} shown by the wavy line in FIG. Although it rises, it cannot be denied that the luminance is insufficient compared to the luminance directly above the fluorescent lamp 1. On the other hand, when the reflective member 5 of the present invention having an opening is provided at the central position between the lamps, the normal direction luminance is at the positions of the openings 6 and 7, as shown by the solid line in FIG. It has a peak of about 7500 cd / m ² and can approach the luminance peak directly above the fluorescent lamp 1.

  Actually, the light is further diffused and propagated inside the housing 2 by the diffusion plate having a thickness of about 2 mm as described above, and further, the dot object formed on the back surface of the diffusion plate and the light curtain are illustrated. The luminance peaks thus smoothed out and the luminance non-uniformity is alleviated. Actually, since the luminance peak directly above the fluorescent lamp 1 is extremely higher than other portions, a dot object that absorbs light in this portion is formed. Accordingly, light absorption occurs, resulting in a decrease in light emission efficiency. However, according to the present invention, the luminance at the positions of the openings 6 and 7 of the reflecting member 5 can be brought close to the luminance peak immediately above the fluorescent lamp 1, so that the pseudo light source is formed between the lamps. As a result, light absorption can be relaxed and a uniform light emitting surface can be provided without lowering the light emission efficiency.

  In the above description, as shown in FIG. 1, the case where two fluorescent lamps 1 are provided as the light source of the backlight unit has been described as an example, but the number of lamps is not limited to two, Even if there are three or more, the effect of the present invention can be obtained by providing the same reflecting member 5 between adjacent lamps. Further, the number of fluorescent lamps 1 may be one, a U-shaped tube as shown in FIG. 10, or an N-shaped tube or a W-shaped tube (not shown), and at least two straight tube portions. If the same is present, the effect of the present invention can be obtained by providing the same reflecting member 5 between the adjacent straight pipe portions. Further, the opening is not necessarily rectangular, and may be circular as shown in FIG.

<Second Embodiment>
A second embodiment of the present invention will be described. FIG. 12 is a top view of the backlight unit according to the second embodiment with the diffusion plate omitted.

  As shown in FIG. 12, in the backlight unit according to the second embodiment, the left and right side walls 14 and 15 of the reflecting member 5 have openings formed by a collection of a large number of minute holes, for example, holes around 1 mm. 17 and 18 are provided. A large number of minute holes are randomly arranged at a high density, but when viewed as a group of holes, that is, in units of the openings 17 and 18, the openings 6 and 7 of the first embodiment (FIG. 1A). The central axis of the openings 17 (or 18) is parallel to the tube axis of the fluorescent lamp 1.

  According to the second embodiment, as in the first embodiment, the secondary light source that allows the bottom wall of the reflecting member 5 to be seen through the openings 17 and 18 is the fluorescent lamp 1 that is a real light source (primary light source). Similarly, it is formed in a straight tube shape. Further, according to the second embodiment, since the emitted light from the fluorescent lamp 1 is shuffled when passing through the minute holes of the openings 17 and 18, for example, the luminance generated in the fluorescent lamp 1 itself. Spots and color spots can be suppressed, and a more uniform light emitting surface can be provided.

These are the top view (a) which abbreviate | omits the diffusion plate of the backlight unit which concerns on 1st Embodiment, and side sectional drawing (b) of the same backlight unit. These are perspective views which show the reflecting plate and reflecting member of the backlight unit. These are the top view (a) of the diffusion plate back surface which shows the example which provided the dot-shaped light reflection material in the back surface of the diffusion plate of the backlight unit, and side sectional drawing of the backlight unit. These are side surface sectional drawings of the backlight unit which show the example which provided the film which gave the light reflection dot behind the diffusion plate of the backlight unit. These are the sectional view on the AA line in FIG. 1 (a) and the enlarged view (b) in FIG. These are the top views which showed the positional relationship of the opening part provided in the right-and-left side wall of the reflection member of the backlight unit. FIG. 5 is a cross-sectional view showing the position in the height direction of the opening provided on the left and right side walls of the reflecting member of the backlight unit. These are the top view (a) and side surface sectional drawing (b) explaining the experiment machine for the normal direction brightness | luminance measurement of the backlight unit. These are figures which show the result of having measured the brightness | luminance of the normal direction using the experimental machine shown in FIG. These are top views which abbreviate | omit the diffuser plate of the other example of the backlight unit, and show an example in which the fluorescent lamp is a U-shaped light source. These are top views which abbreviate | omit the diffuser plate of the further another example of the same backlight unit, Comprising: The opening provided in the right-and-left side wall of a reflection member shows the example circular. These are top views which abbreviate | omit and show the diffuser plate of the backlight unit according to the second embodiment. These are the circuit diagrams of an example of the lighting circuit apparatus used for a backlight unit. These are side surface sectional views which show schematic structure of a general backlight apparatus. These are side surface sectional views which show schematic structure of the conventional backlight apparatus described in patent document 1 and patent document 2. FIG. These are explanatory drawings which show a mode that the light from a fluorescent lamp is diffusely reflected by the triangular prism-shaped reflection member in the backlight apparatus shown in FIG. FIG. 16 is a diagram illustrating a luminance distribution in a normal direction in a direction orthogonal to the tube axis of the fluorescent lamp in the backlight device illustrated in FIG. 15. FIG. 15 shows the backlight device shown in FIG. 15 in which a hot cathode tube is used as a fluorescent lamp, and when the inclination angle of the side surface of the reflecting member is steep (a) and gentle (b), It is a figure which compares and represents the luminance distribution of a normal line direction about the direction orthogonal to an axis | shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluorescent lamp 2 Case 3 Reflecting sheet (one aspect of reflecting plate)
4 Diffuser 5 Reflecting member 6, 7 Opening 14 Left side wall 14a First reflecting surface 15 Right side wall 15a Second reflecting surface 16 Bottom wall 16a Third reflecting surface 17, 18 Opening made of minute holes

Claims (2)

A tubular fluorescent lamp supported on a reflector and having at least two straight tube portions arranged in parallel;
A diffusion plate disposed above the fluorescent lamp;
A reflecting member disposed parallel to the tube axis at a central position between the adjacent straight pipe portions on the reflecting plate;
In the backlight device,
The reflecting member has a triangular cylindrical shape having a cavity inside, and a plurality of openings periodically arranged at a predetermined pitch in the tube axis direction are formed on each side wall of the reflecting member facing each of the adjacent straight pipe portions. A backlight device provided with a half-pitch shift.   The backlight device according to claim 1, wherein the opening is an aggregate of a plurality of minute holes.

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