Patent Application
20090059562
The present invention relates to a backlight unit having multiple lamps each formed in a substantial U-shape and a substantially U-shaped lamp for a backlight unit.
Direct type backlight units that have multiple lamps each bent in a substantial U-shape as light source are used, for example, in LCD (liquid crystal display) apparatuses. The reason that substantially U-shaped lamps have been adopted in backlight units is because the number of lamps required can be reduced by half as compared to the case where straight lamps are used, which leads to an improvement in the lamp installation efficiency.
In common backlight units, substantially U-shaped lamps are arranged in parallel to each other in an envelope in a manner that the end portions of all the lamps are positioned on the same side, either left or right. However, the end portions being disposed on a single side means the concentration of the electrodes on the side. Since the electrodes are the source of heat generation, a difference in temperature is produced between the left and right sides of the envelope. The temperature difference affects the mercury vapor pressure of the lamps and accordingly induces unevenness of luminance in the backlight unit.
Regarding this issue, Patent Reference 1 discloses a backlight unit 100 in which end portions 111a and 111b of each curved lamp 110 face opposite to end portions 111a and 111b of the adjacent curved lamp 110, as shown in
In the envelope 120 of the backlight unit 100, rubber holders 180 are provided on the left and right sides. Here, the lamps 110 are installed with the end portions 111a and 111b inserted into insertion holes 181 of the holders 180 and bent portions 113 of the lamps 110 fitted into engaging grooves 182 of the holders 180. In
<Patent Reference 1> Japanese Laid-Open Patent Application No. 2004-327328
With the backlight unit 100, however, light emitted from the bent portions 113 cannot be efficiently taken out from the envelope 120 because the bent portions 113 are positioned outside the light take-out region 121, and accordingly electric power for operating the bent portions 113 is wasted.
However, if the light take-out region 121 is expanded in width so as to include the bent portions 113 therein, the end portions 111a and 111b hardly emitting light are also included in the light take-out region 121. As a result, dark regions due to the end portions 111a and 111b are extensively formed in the light take-out region 121.
In general, the backlight unit 100 is designed so that luminance is uniformly distributed over bright regions that emit light and dark regions that hardly emit light, using a translucent plate (not shown). However, the dark regions formed due to the end portions 111a and 111b are actually so extensive that the translucent plate is ineffectual to distribute the luminance uniformly. As a result, the dark regions still remain, causing unevenness in luminance.
In view of the above issues, the present invention aims to provide a backlight unit realizing reduced unevenness in luminance and requiring less power consumption.
In order to solve the above problems, the backlight unit of the present invention is characterized in that a plurality of substantially U-shaped lamps, each including two end portions and a bent portion, are disposed in parallel to one another in an envelope in a manner that the end portions of each of the lamps face opposite to the end portions of an adjacent one of the lamps. Here, electrodes are respectively attached to each of the end portions. The end portions of each of the lamps are positioned closer to a side wall of the envelope than the bent portion of the adjacent one of the lamps is.
In addition, the backlight unit of the present invention is characterized in that the bent portion of each of the lamps is positioned within a light take-out region of the envelope, and the end portions of each of the lamps may be positioned outside the light take-out region.
Furthermore, the backlight unit of the present invention is characterized in that the end portions and the electrodes of each of the lamps are housed in a socket positioned outside the light take-out region.
Furthermore, the backlight unit of the present invention is characterized in that part of each of the lamps, which has a less than 70% relative luminance to the bent portion, is positioned outside the light take-out region.
Furthermore, the backlight unit of the present invention is characterized by including a supporting member operable to support the lamps in the envelope. Here, a reflection layer for reflecting light from the lamps toward a light take-out opening of the envelope is positioned at part of the supporting member, which is in contact with the lamps.
The substantially U-shaped lamp for a backlight unit of the present invention is characterized in that, in the backlight unit, a plurality of substantially U-shaped lamps, each including two end portions and a bent portion, are disposed in parallel to one another in an envelope of the backlight unit in a manner that the end portions of each of the lamps face opposite to the end portions of an adjacent one of the lamps and are positioned closer to a side wall of the envelope than the bent portion of the adjacent one of the lamps is. An electrode is attached to each of the end portions. Here, A−W+3≦L≦A−W/3+3 is satisfied, where A [mm] is an extent of a light take-out region of the backlight unit in a direction perpendicular to a direction in which the lamps are disposed in parallel to one another, W [mm] is a space between paired straight tube portions of each of the lamps, and L [mm] is a distance from a tip of the electrode to an edge of the bent portion in the perpendicular direction.
According to the backlight unit of the present invention, since both end portions of each lamp are positioned closer to the side wall of the envelope than the bent portion of the adjacent lamp is, it is easy to dispose the bent portion, which emits light, within the light take-out region while disposing the paired end portions, which emit no light, outside the light take-out region. As a result, the backlight unit of the present invention readily facilitates a reduction in power consumption, efficiently using the light emitting parts to the fullest extent. In addition, extensive dark regions are less likely to be formed over the light take-out region, and consequently unevenness in luminance is less likely to occur.
Particularly, in the case where the bent portion of each lamp is disposed within the light take-out region and the end portions are disposed outside the light take-out region, the light emitting parts of each lamp can be efficiently used, whereby realizing a further reduction in power consumption and therefore further reducing the unevenness in luminance.
In addition, in the case where both end portions and electrodes of each lamp are housed in a socket provided outside the light take-out region, extensive dark regions hardly emitting light are less likely to be formed, and consequently unevenness in luminance is further less likely to occur.
Unevenness in luminance caused by parts having a less than 70% relative luminance to the bent portion is difficult to suppress with the use of a translucent plate. Therefore, in the case where such parts are disposed outside the light take-out region, unevenness in luminance is significantly less likely to occur.
In addition, in the case where the backlight unit includes a supporting member, on which a reflection layer for reflecting light from the lamps toward the light take-out opening of the envelope is formed, light emitted from the lamps are efficiently taken out even if the supporting member is positioned within the light take-out region.
The substantially U-shaped lamp for a backlight unit of the present invention satisfies A−W+3≦L≦A−W/3+3, where A [mm] is an extent of a light take-out region of the backlight unit in the direction perpendicular to the direction in which the lamps are disposed in parallel to one another, W [mm] is a space between paired straight tube portions of each of the lamps, and L [mm] is a distance from a tip of the electrode to an edge of the bent portion in the perpendicular direction. As a result, when the lamp is installed in the envelope of a backlight unit, light emitted from the lamp can be efficiently taken out from the light take-out opening of the envelope.
The backlight unit 1 includes multiple cold cathode fluorescent lamps 10 (hereinafter, simply referred to as the “lamps 10”) each formed in a substantial U-shape. Each lamp 10 has paired end portions 11a and 11b, to each of which an electrode 12 is provided, and a bent portion 13 on the opposite side to the paired end portions 11a and 11b. Here, the lamp in a substantial U-shape means a lamp having the paired end portions 11a and 11b on one side and the bent portion 13 on the other. The bent portion may be formed in a circular arc shape with a single corner, or may have two substantially perpendicular corners with a straight in between. Note that a lamp having a glass bulb which is formed by bridge-connecting two straight glass tubes at one end of these respective tubes is one type of the substantially U-shaped lamps.
All lamps 10 are arranged inside an envelope 20, aligning in parallel to each other in the up-and-down direction with the both end portions 11a and 11b of each lamp 10 facing opposite to the end portions 11a and 11b of the adjacent lamp 10. The envelope 20 includes a reflecting plate 30, a side plate 40, a mounting frame 50 and a translucent plate 60.
The reflecting plate 30 is a square board made of PET (polyethylene terephthalate) resin, and is disposed on the back side of the lamps 10, as shown in
Now referring back to
As shown in
The translucent plate 60 is formed by layering a diffuser plate 61, a diffuser sheet 62 and a lens sheet 63 in the stated order from the back side. The diffuser plate 61 is a square board made of PC (polycarbonate) resin. The diffuser sheet 62 is a sheet also made of PC resin. The lens sheet 63 is an acrylic resin sheet. On the diffuser plate 61, a dot pattern 64 is provided according to the arrangement of the lamps 10—more specifically speaking, according to the contour of the respective lamps 10 that align in parallel to one another with the end portions of each lamp 10 facing opposite to the end portions of the adjacent lamp 10. Accordingly, light emitted from the lamps 10 is diffused when passing through the diffuser plate 61, and then uniformly emitted from the entire surface of the diffuser plate 61.
Since the mounting frame 50 is made of an opaque material, light inside the envelope 20 has to pass through the opening 51 to go out to the front side of the envelope 20. The part enclosed by the two-dot chain line in
As shown in
In addition, the right-hand edge of the opening 51 substantially coincides with the edge, facing inward of the envelope 20, of the clip-holding pieces 45a and 45b provided on the right side member 42 of the side plate 40. Also, the right-hand edge of the opening 51 substantially coincides with the edge, facing inward of the envelope 20, of the bush 70 disposed between the clip-holding pieces 45a and 45b provided on the right side member 42 of the side plate 40. The left-hand edge of the opening 51 substantially coincides with the edge, facing inward of the envelope 20, of the clip-holding pieces 45a and 45b provided on the left side member 44 of the side plate 40. Also, the left-hand edge of the opening 51 substantially coincides with the edge, facing inward of the envelope 20, of the bush 70 disposed between the clip-holding pieces 45a and 45b provided on the left side member 44 of the side plate 40.
When viewed from the upper or lower side of the envelope 20, the light take-out region 21 is the part enclosed by the two-dot chain line in
Note that each dimension of the lamp 10 is not limited to the above value; however, it is preferable that, for example, Dimension L1 of the total length be in the range of 130 mm to 700 mm and Dimension W of the space between the straight tube portions 14a and 14b be in the range of 9 mm to 33 mm. In addition, each dimension of the glass bulb 15 is not limited to the above value; however, the outer diameter is preferably in the range of 1.8 mm to 6.0 mm (the inner diameter: 1.4 mm to 5.0 mm), for example. Furthermore, the cross section of the glass bulb 15 is not necessary to be substantially circular, and may be a flat-shaped cross section, such as an ellipse.
On the internal surface of the glass bulb 15, a phosphor layer 16 is formed. The phosphor layer 16 is a rare earth phosphor made, for example, of a red phosphor (Y2O3:Eu), a green phosphor (LaPO4:Ce,Tb) and a blue phosphor (BaMg2Al16O27:Eu,Mn). The glass bulb 15 is filled with approximately 3 mg of mercury (not shown) and a mixed gas of neon and argon (Ne 95%+Ar 5%), as a rare gas, at the gas pressure of 60 Torr.
Note that the phosphor layer 16, mercury, and rare gas are not limited to the above compositions; for instance, a mixed gas of neon and krypton (Ne 95% Kr 5%) may be enclosed as a rare gas. By adopting the mixed gas of neon and krypton as a rare gas, the starting performance of the lamps 10 can be improved and accordingly the lamps 10 can be lit with low voltage.
Onto each end portion 11a/11b of the lamp 10, a lead wire 17 is fixed. The lead wire 17 is a joint wire of an internal tungsten lead wire 18 and an external nickel lead wire 19. The glass bulb 15 is air-tightly sealed, with the lead wire 17 is attached thereto, at the internal lead wire 18. Note that the internal lead wire 18 and the external lead wire 19 respectively have a substantially circular cross section.
To an end of the internal lead wire 18 on the inner side of the glass bulb 15, the electrode 12 is joined by laser welding or the like. The electrode 12 is a so-called hollow electrode in a tubular shape with a bottom, and is fabricated from a niobium (Nb) rod. The electrode 12 is, for example, 5.5 mm in total length, 1.7 mm in outer diameter, 1.5 mm in inner diameter and 0.1 mm in tube wall thickness.
Note that the electrode 12 does not have to be made of niobium, and may be made of nickel (Ni), tantalum (Ta), or molybdenum (Mo), for example. In addition, although the hollow electrode in a tubular shape with a bottom is used as the electrode 12 above, the shape of the electrode is not limited to this. Instead, an electrode in a cylindrical shape or a plate-like electrode in a narrower strip shape may be used. The reason that a hollow electrode has been adopted as the electrode 12 is because it is effective to reduce electrode sputtering caused by discharge during the period when the lamp is lit (for details, see Japanese Laid-Open Patent Application No. 2002-289138).
On the outer circumference of the bush 70, multiple ribs 75 are provided in a protruding fashion, as shown in
Thus, the bush 70 is attached to each of the end portions 11a and 11b of the lamp 10, and the respective bushes 70 are independent from each other. As a result, the heat of the lamp 10 is less likely to be conducted away therefrom as compared to the case of the conventional backlight unit 100 of
In addition, when the distance from the tip 15a of the glass bulb 15 is less than 10 mm, the relative luminance falls short of 70%, as shown in
Note that the relative luminance falls short of 50% when the distance from the tip 15a of the glass bulb 15 is less than 8 mm. The part having a relative luminance of less than 50% is a non-light emitting part which is not suitable for the use as a light source, and it is therefore preferably disposed outside the light take-out region 21.
As shown in
On the other hand, as Dimension D3 is larger, dark regions emitting no light within the light take-out region 21 increase. When the extent of the dark regions becomes excessively large, unevenness in luminance occurs since the translucent plate 60 cannot distribute it uniformly any more. In order not to cause unevenness in luminance, it is desirable to set Dimension D3 to 25 mm or less.
Furthermore, in terms of Dimension W of the space between the straight tube portions 14a and 14b of the lamp 10, it is desirable that Dimension D3 satisfy the following Equation 1. This realizes a well-balanced arrangement of the lamps 10, and accordingly light emitted from the lamps 10 can be uniformly diffused by the diffuser plate 61.
W/3≦D3≦W (Equation 1).
Note that it is further preferable to set W/3 to 2 mm or more since a reduction in lamp power can be achieved if Dimension D3 is 2 mm or more, as shown in
Thus, it is preferable that Dimension D3, the distance from the bent portion 13 to the edge of the light take-out region 21, satisfy Equation 1 above. In addition, Dimension D6, the distance from the edge of the electrode 12 facing inward of the envelope 20 (i.e. a tip 12a of the electrode 12) to the edge of the bush 70 facing inward of the envelope 20 (i.e. the boundary of the light take-out region 21), is 3 mm, as described above. Therefore, in order to dispose the part of the lamp 10 having a relative luminance of less than 70% outside the light take-out region 21, it is desirable that the part between the tip 12a of the electrode 12 and less than 3 mm inward of the envelope 20 from the tip 12a be disposed outside the light take-out region 21. Therefore, if the following Equation 2 is satisfied, light emitted from the lamps 10 can be efficiently taken out from the light take-out opening of the envelope 20.
A−W+3≦L≦A−W/3+3 (Equation 2),
where A is the extent of the light take-out region 21 in the left-and-right direction, as described above, and L is the distance from the tip 12a of the electrode 12 to the edge 13a of the bent portion 13 in the left-and-right direction of the lamp 10 (i.e. the direction perpendicular to the direction in which the lamps 10 are laid in parallel to each other).
As shown in
Note however that Dimension D4 does not have to be substantially the same as Dimension W, and unevenness in luminance can be sufficiently suppressed by the diffuser plate 61 if it is within the range of 0.8 to 1.2 times the Dimension W.
As shown in
Supporting members 80 are vertically provided on the reflecting plate 30, as shown in
Each supporting member 80 is made of white PET resin, and has an engaging portion 81 with a C-shaped cross section at the top, as shown in
On a part of the supporting member 80 which comes in contact with the lamp 10, i.e. the inner surface of the engaging portion 81, a heat insulating layer 82 and a reflection layer 83 are integrally formed in the stated order.
The heat insulting layer 82 is made of Teflon (registered trademark), and functions as a heat insulating agent between the lamp 10 and the supporting member 80. Note that the material of the heat insulating layer 82 is not limited to Teflon (registered trademark), and a material having a lower heat conductance than gas, i.e. air, filled in the envelope 20.
The heat of parts of the lamp 10 that are held by the supporting members 80 is transmitted to the envelope 20 via the supporting members 80. When the temperature of the parts held by the supporting members 80 decreases, these parts become the coldest spots, and consequently an adequate mercury vapor pressure cannot be achieved anymore. Therefore, the heat insulating layer 82 is provided to prevent a decrease in the temperature of the lamp 10.
The reflection layer 83 functions as a reflecting member for reflecting light of the lamp 10 towards the opening 51 of the mounting frame 50. In the backlight unit 1 of the present embodiment, since the bent portions 13 of the lamps 10 are disposed within the light take-out region 21, the bent portions 13 have to be supported within the light take-out region 21. Accordingly, in order to efficiently use light emitted from the bent portions 13, it is desirable to provide the reflection layer 83 to each supporting member 80. Note that the supporting members 80 are provided on the reflecting plate 30 side so as not to intercept light emitted toward the opening 51.
Since each of the lamps 10 is supported by the supporting members 80 at the bent portion 13 and the straight tube portions 14a and 14b, the backlight unit 1 allows positioning of the lamps 10 with high accuracy.
The present invention has been described based on the present embodiment; it is a matter of course, however, that the present invention is not limited to the embodiment. For example, the following cases are also within the scope of the present invention.
In the above embodiment, the lamps 10 are arranged in parallel to each other in a manner that the straight tube portions 14a and 14b are laid in the left-and-right direction. However, the present invention is not limited to this case, and the lamps 10 may be arranged in parallel to each other in a manner that the straight tube portions 14a and 14b are laid in the up-and-down direction.
In the above embodiment, the lamps are cold cathode fluorescent lamps. However, the present invention is not limited to this case, and external electrode fluorescent lamps, hot cathode fluorescent lamps, or lamps having no phosphor layer may be used instead.
The backlight unit of the present invention is, for example, applicable to liquid crystal display apparatuses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-122746 | Apr 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/306559 | 3/29/2006 | WO | 00 | 9/18/2007 |
