JPWO2008136307A1 - Direct type backlight - Google Patents

Abstract

A back frame 1b having a low opening, a plurality of fluorescent lamps 2 having a diameter R of 6.0 mm or more arranged inside the back frame 1b, and a diffusion plate 3 arranged in the opening lb3 of the back frame 1b. Thus, when the pitch of the adjacent fluorescent lamps 2 is P (mm), the relationship of P ≧ 3.5R is satisfied.

Description

  The present invention relates to a direct type backlight mainly used for a large liquid crystal display or the like.

  As a light source used for a liquid crystal display or the like, a linear light source having a small diameter such as a cold cathode fluorescent lamp or an external electrode fluorescent lamp is mainly used. However, in recent years, a backlight using a hot cathode fluorescent lamp having a large diameter has been developed. The reason is that the number of lamps can be reduced because the hot cathode fluorescent lamp has a larger amount of light than the cold cathode fluorescent lamp and the external electrode fluorescent lamp. Backlights using hot cathode fluorescent lamps are disclosed in Japanese Laid-Open Patent Publication No. 8-17397 (hereinafter referred to as Patent Document 1), Japanese Laid-Open Patent Publication No. 9-146094 (hereinafter referred to as Patent Document 2), published in Japan. It is described in Japanese Patent Laid-Open No. 6-67176 (hereinafter referred to as Patent Document 3).

  In a backlight using such a hot cathode fluorescent lamp, it is known that a bright part is likely to occur on the light emitting surface immediately above the lamp and a dark part is easily generated on the light emitting surface between the lamps because the amount of light obtained from the lamp is large as described above. It has been. Therefore, in order to alleviate the dark part between the lamps, it is usual to design the pitch between adjacent lamps to be small.

However, it has been confirmed that when the pitch between adjacent lamps is reduced, the luminance efficiency of the light emitting surface decreases. As a result of the study by the present inventors, it has been found that the reduction in the luminance efficiency of the light emitting surface causes a loss due to the emitted light being absorbed by the lamp itself. Further, it has been found that the decrease in luminance efficiency due to the light absorption is particularly problematic when the lamp diameter is 6.0 mm or more.
Japanese Laid-Open Patent Publication No. 8-17397 Japanese Laid-Open Patent Publication No. 9-146094 Japanese Laid-Open Patent Publication No. 6-67176

  An object of the present invention is to provide a direct type backlight using a fluorescent lamp having a large diameter and having high luminance efficiency on a light emitting surface.

  In order to achieve the above object, a direct backlight according to the present invention includes a case with a bottomed opening, a plurality of fluorescent lamps having a diameter R of 6.0 mm or more arranged inside the case, And an optical member disposed in the opening, and satisfying the relationship of P ≧ 3.5R, where P (mm) is the pitch of the adjacent fluorescent lamps.

  According to the present invention, it is possible to provide a direct type backlight having high luminance efficiency on the light emitting surface.

1 is an exploded perspective view of a direct type backlight according to a first embodiment of the present invention. FIG. FIG. 2 is a cross-sectional view of the direct type backlight of FIG. 1 cut along the line AA. The longitudinal cross-sectional view which shows the structure of a hot cathode fluorescent lamp. The graph which shows the change of relative lamp | ramp efficiency when changing lamp electric power about the fluorescent lamp from which diameter R differs. The figure for demonstrating the optical path of light when a fluorescent lamp with a large diameter R is used. The graph which shows the change of relative board surface luminance efficiency when the lamp pitch P is changed about the fluorescent lamp from which the diameter R differs. The graph which shows the relationship between the lamp pitch P when the brightness nonuniformity is suppressed and the distance L2 between the diffuser plates in a lamp having a diameter R of 6.0 mm to 15.5 mm.

  Hereinafter, a direct backlight according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a direct type backlight according to the first embodiment, and FIG. 2 is a cross-sectional view taken along line AA of the direct type backlight of FIG.

  The casing of the direct type backlight according to the present embodiment includes a front frame 1a and a back frame 1b. As the material, a metal such as aluminum or a white plastic such as polycarbonate can be used. The front frame 1a is formed with a light output portion 1a1 that serves as a light emitting surface of the backlight, and forms a lid of the casing as a whole. The back frame 1b is a bottomed opening-shaped casing having a bottom 1b1, a side 1b2, and an opening 1b3. A reflective sheet having high reflectivity is formed inside the bottom 1b1 and the side 1b2.

  Inside the back frame 1b, a plurality of straight tube type fluorescent lamps 2 are arranged, and the respective tube axes are arranged substantially in parallel. The fluorescent lamp 2 is a hot cathode fluorescent lamp as shown in FIG. The container is composed of, for example, a glass tube 21 made of soft glass and having a diameter R of 6.0 to 20.0 mm. The glass tube 21 includes a cylindrical portion 21a and flare stem portions 21b formed at both ends thereof. Mercury and a rare gas are sealed inside the glass tube 21 as a discharge medium. As the rare gas, argon, xenon, neon or the like can be used alone or in combination. A phosphor 22 is applied to the inner peripheral surface of the cylindrical portion 21a. Introducing wires 23a and 23b are sealed in the flare stem portion 21b in the inner and outer directions of the fluorescent lamp 2. In general, the lead-in wires 23a and 23b are each composed of a pair of conductive wires. Filaments 24a and 24b made of a spiral tungsten wire are connected to the leading ends of the introduction wires 23a and 23b located in the glass tube 21. In the filaments 24a and 24b, the vicinity of the approximate center between the introduction lines 23a and 23b is further formed in a spiral shape. It has been applied. The filaments 24a and 24b are connected by turning the leading ends of the introduction wires 23a and 23b and crimping both ends of the filaments 24a and 24b. At that time, the introduction lines 23a and 23b for caulking the filaments 24a and 24b have a substantially semi-elliptical cross section with a partly flat surface, so that the connection strength by caulking is high. Such a shape can be formed by flattening a part of a conductive wire having a circular cross section, and the diameter of the introduction lines 23a and 23b on the flat surface is 30 to 90% of the diameter before processing. Is desirable.

  In FIG. 1, a diffusion plate 3 as an optical member is disposed in parallel with the opening 1b3 of the back frame lb. The diffusion plate 3 is desired to have a transmittance of 50% to 85%. This is because unevenness in light emission can be reduced and the efficiency does not decrease too much.

  Here, in this embodiment, the fluorescent lamp 2 is arranged to reduce the luminance difference between the fluorescent lamp 2 and the vicinity of the center between the adjacent lamps in order to suppress striped luminance unevenness generated on the light emitting surface. The means to do is adopted.

  The first means is a method of arranging a plurality of fluorescent lamps 2. The plurality of fluorescent lamps 2 are arranged so that the relationship between the lamp diameter R (mm) and the pitch between adjacent lamps P (mm) satisfies P ≧ 3.5R. Further, the relationship between the distance L1 (mm) between the bottom 1b1 (reflection surface) of the back frame 1b and the fluorescent lamp 2 is L1 ≧ 0.2R. With such an arrangement method, even when a large-diameter lamp having a diameter R of 6.0 mm or more is used, loss due to light entering the lamp can be reduced, and the luminance efficiency of the backlight is increased. be able to.

  The second means is the use of a diffusing plate 3 on which dot printing is performed along the lamp axis of the fluorescent lamp 2. The diffusion plate 3 is formed so that the size of the dots gradually decreases as it goes toward the center between the lamps, and the unevenness in luminance can be further suppressed by adjusting the amount of emitted light from directly above the lamps to between the lamps.

  An optical sheet may be further disposed on the diffusion plate 3. As the optical sheet, one sheet or a plurality of sheets such as a diffusion sheet, a prism sheet, and a polarizing sheet can be used according to the purpose.

  The specific specification of the backlight concerning the Example of this invention is shown below.

(Example 1)
Backlight; Size = 32 inches (approx. 760 mm x approx. 440 mm), effective light emission area = 700 mm x 400 mm, internal thickness D = 20.0 mm
Fluorescent lamp 2; Hot cathode fluorescent lamp, inner diameter = 6.9mm, diameter R = 8.0mm, lamp current = 70mA, number of lamps used = 8, lamp pitch P = 50.0mm, fluorescent lamp 2 and bottom 1b1 of back frame 1b Distance L1 = 2.0mm, distance L2 = 10.0mm from diffusion plate 3, distance L3 = 20.0mm from side 1b2.
Diffuser 3; Transmittance = 60%, dot printing on the part directly above the fluorescent lamp 2,
Optical sheet; Diffusion sheet

  FIG. 4 is a graph showing changes in relative lamp efficiency when the lamp power is changed for fluorescent lamps having different diameters R. Here, the diameter R = 3.0 mm is a cold cathode fluorescent lamp, and the diameter R = 6.0 to 15.5 mm is a hot cathode fluorescent lamp. The relative lamp efficiency is based on the lamp efficiency (lm / W) when a cold cathode fluorescent lamp having a diameter R = 3.0 mm is lit at 6.0 W.

  As can be seen from this graph, the relative lamp efficiency does not change much at the lamp diameters R = 6.0 mm and 8.0 mm, but the relative lamp efficiency tends to increase at larger diameters. R = 10.0mm improves about 20% and R = 15.5mm improves about 30%. In addition, as the lamp diameter R increases, the power that can be supplied increases. In other words, the amount of light obtained from a lamp increases, and compared to a lamp with a diameter R = 3.0 mm, the lamp with an R = 6.0 mm is approximately twice, the lamp with R = 8.0 mm is approximately 2.5 times, and R = 10.0. A light amount of about 3.0 times can be obtained for mm, and a light amount of about 4.0 times can be obtained for R = 15.5 mm. Therefore, if a lamp having a large diameter R is used, it is theoretically possible to realize a bright backlight while reducing the number of lamps.

  However, as a result of the inventors' tests, it has been found that when the fluorescent lamp 2 having a large diameter R is used, the luminance efficiency of the backlight may be extremely low. The cause is considered as follows.

  As shown in FIG. 5, there are three types of light emitted from the fluorescent lamp 2, light X reflected by the bottom 1b1 (reflecting surface), light Y reflected by the diffuser 3, and light Z not reflected by them. Can be broadly divided. Further, the light X can be divided into light X1 that is reflected by the bottom 1b1 and then transmitted through the diffusion plate 3, light X2 that is incident on the fluorescent lamp 2 itself, and light X3 that is incident on another fluorescent lamp 2. Further, the light Y can be divided into light Y1 that is reflected by the diffusion plate 3 and then transmitted through the diffusion plate 3, light Y2 that is incident on the fluorescent lamp 2 itself, and light Y3 that is incident on another fluorescent lamp 2. Further, the light Z can be divided into light Z1 that directly reaches and passes through the diffusion plate 3, and light Z2 that directly enters another fluorescent lamp 2.

  Among the lights X to Z, the lights X1, Y1, and Z1 are used as backlight light. On the other hand, the light X2, X3, Y2, Y3, Z2 incident on the fluorescent lamp 2 itself or another fluorescent lamp 2 is lost. Therefore, it is better to reduce these lights as much as possible. Since the lights X2, X3, Y2, Y3, and Z2 are incident on the fluorescent lamp 2 itself or other fluorescent lamps 2, they are most affected by the diameter R of the lamp. That is, in the cold cathode fluorescent lamp, the light X2, X3, Y2, Y3, Z2 is small because the probability of light entering the lamp is low, but in the hot cathode fluorescent lamp, the light X2, X3, Y2, Y3, Z2 is large. . As a result of the inventor's test, it was found that when the diameter R of the fluorescent lamp 2 is 6.0 mm or more, the light X2, X3, Y2, Y3, and Z2 increase, which causes a decrease in efficiency.

  In order to reduce the light X2, X3, Y2, Y3, Z2 using such a large fluorescent lamp 2, the lamp pitch P, the distance L1 between the fluorescent lamp 2 and the bottom 1b1, the fluorescent lamp 2 and the diffusion plate 3 The distance L2 is important. This is because the lamp pitch P is greatly related to the generation of the light X3, Y3 and Z2, the distance Ll is the light X2, and the distance L2 is largely related to the generation of the light Y2. Therefore, a test was performed in which the lamp pitch P and the like were changed for each diameter R of the fluorescent lamp 2.

  FIG. 6 is a graph showing the change in relative plate surface luminance efficiency when the lamp pitch P is changed for fluorescent lamps having different diameters R. In this test, the number of lamps equal to the value obtained by dividing the inner dimension of the frame of the 32-inch backlight by 400 mm by the lamp pitch P was arranged. That is, when the lamp pitch P was selected as 40 mm, the test was performed with 10 lamps, 8 when 50 mm was selected, and 5 lamps when 80 mm was selected. Here, the relative plate surface luminance efficiency means that when each lamp is lit at 6.0 W in a 32-inch backlight in which a cold cathode fluorescent lamp having a diameter R = 3.0 mm has a lamp pitch P = 20 mm and 20 lamps are arranged. This is based on the plate surface luminance efficiency (cd / W) obtained.

  As can be seen from the graph, the relative plate surface luminance efficiency is improved as the lamp pitch P is increased in all the lamps. However, in a lamp having a diameter R larger than 6.0 mm, the relative plate surface luminance efficiency may be lower than 100% depending on the lamp pitch P. That the relative plate surface luminance efficiency is lower than 100% means that the luminance efficiency is low. Therefore, in order to realize a backlight having a high luminance, it is necessary to use at least a condition where the relative plate surface luminance efficiency exceeds 100%. To that end, from Fig. 6, the lamp pitch P is about 23.0 mm or more when the diameter R is 6.0 mm, about 28.0 mm or more when R = 8.0 mm, about 37.0 mm or more when R = 10.0 mm, R = In the case of 15.5mm, it is necessary to make it about 55.0mm or more. In this case, the lamps may be arranged so as to satisfy P ≧ 3.5R. In addition, it is desirable to arrange the lamp so as to satisfy P ≧ 4.5R because the luminance efficiency is further improved. However, if the lamp pitch P is excessively increased with respect to the diameter R, the luminance of the backlight is lowered and luminance unevenness is increased. Therefore, it is desirable to set P ≦ 13.0R as the upper limit.

  The distance L1 between the fluorescent lamp 2 and the bottom 1b1 is preferably L1 ≧ 0.2R, and more preferably designed to satisfy L1 ≧ 0.4R. Thereby, since the ratio of reflected light entering the lamp is reduced, the luminance efficiency can be further improved. However, if the distance L1 on the left side in the relational expression becomes too large, the internal thickness D becomes large, causing adverse effects such as an increase in the thickness of the backlight.Therefore, designing within the range of L1 ≦ 1.0R is necessary. desirable.

(Example 2)
In this example, the configuration is basically the same as that of Example 1, but a normal diffusion plate is used, and the distance L2 between the fluorescent lamp 2 and the diffusion plate 3 satisfies L2 ≧ 0.45P-0.5R. Designed to. Specifically, the lamp diameter R = 8.0 mm and the lamp pitch P = 50 mm, while the distance L2 is 19.0 mm (internal thickness D = 29.0 mm). Surprisingly, it has been found that, according to this design, luminance unevenness can be suppressed as in Example 1 without using a diffusion plate that has been subjected to special processing such as dot printing.

  Note that the above formula is not limited to the case of the lamp diameter R = 8.0 mm, but also holds for other diameters R. FIG. 7 is a graph showing the relationship between the lamp pitch P and the distance L2 between the diffuser plate when uneven brightness is suppressed in a lamp having a diameter R of 6.0 mm to 15.5 mm. Here, “brightness unevenness has been suppressed” means that the brightness unevenness cannot be confirmed visually. Specifically, when the brightness difference between the lamp and the lamp is 40 cd / mm2 or less. Indicates.

  As can be seen from FIG. 7, even when the diameter R is 6.0 mm, 10.0 mm, and 15.5 mm, if L2 = 0.45P-0.5R is satisfied, the luminance difference between the lamp and the lamp is 40 cd / mm2. . Therefore, even when the diameter R is 6.0 mm or more, luminance unevenness can be suppressed by designing so as to satisfy L2 ≧ 0.45P−0.5R. It is desirable that L2 ≧ 0.50P−0.5R because the luminance difference is 30 cd / mm 2 or less. However, as in the case of the distance L1, if the distance L2 on the left side becomes too large, adverse effects such as an increase in the internal thickness D of the backlight will occur, so it is designed to satisfy L2 ≦ 1.0P-0.5R. Is desirable.

  In this embodiment, a prism sheet may be further arranged on the diffusion plate 3. In this case, if L2 ≧ 0.35P−0.5R is satisfied, a luminance unevenness suppressing effect equivalent to that in the second embodiment can be obtained. For this reason, thickness reduction can also be realized simultaneously.

  Therefore, in the first embodiment, in a direct type backlight in which a plurality of fluorescent lamps 2 having a diameter R of 6.0 mm or more are arranged inside the back frame 1b, the pitch P (mm) between adjacent lamps is set to P ≧ 3, By arranging the fluorescent lamp 2 so as to satisfy the 5R relationship, a direct type backlight with high luminance efficiency on the light emitting surface can be realized. In this case, it is more effective to configure the relationship L1 ≧ 0.2R so that the distance between the bottom 1b1 of the back frame 1b and the fluorescent lamp 2 is L1 (mm).

  Also, by combining with the diffuser plate 3 that is dot-printed along the fluorescent lamp 2, it is possible to eliminate the bright and dark stripes that are likely to occur due to the above configuration, and to realize a direct type backlight with little luminance unevenness be able to. On the other hand, if the distance between the fluorescent lamp 2 and the diffusion plate 3 is L2 (mm), the relationship of L2 ≧ 0.45P-0.5R is satisfied, even if the fluorescent lamp 2 and the diffusion plate 3 are not specially processed. By designing in this manner, it is possible to suppress bright and dark stripes, and to realize an inexpensive direct-type backlight with little luminance unevenness. In addition, the Example of this invention is not necessarily restricted above, For example, you may change as follows.

  The fluorescent lamp 2 may be a cold cathode fluorescent lamp or an outer electrode fluorescent lamp having a diameter R of 6.0 mm or more. The shape is not limited to a straight line, and a bent light source such as a U shape, a U shape, or a W shape can be used. However, the lamp pitch P in the case of a bent fluorescent lamp is also applied between adjacent straight tube portions of the same bent lamp.

  As the processing part for reducing the luminance difference on the light emitting surface, the fluorescent lamp 2 and / or the diffusing plate 3 are provided with a film or molding for shielding, reflecting or reducing the light directly above the lamp. There may be. In Example 2, a prism sheet may be further disposed on the diffusion plate 3. In this case, if L2 ≧ 0.35P−0.5R is satisfied, a luminance unevenness suppressing effect equivalent to that in the second embodiment can be obtained. For this reason, thickness reduction can also be realized simultaneously.

Claims (6)

  A low and high casing having an opening, a plurality of fluorescent lamps having a diameter R of 6.0 mm or more arranged substantially parallel to the inside of the casing, and light emitted from these fluorescent lamps are diffused And an optical member disposed in the opening of the housing, and when the pitch of the adjacent fluorescent lamps among the plurality of fluorescent lamps is P (mm), a relationship of P ≧ 3.5R Direct type backlight characterized by satisfying   2. The direct type backlight according to claim 1, wherein a relationship of L1 ≧ 0.2R is satisfied, where L1 (mm) is a distance between the bottom surface of the housing and the lower surface of the fluorescent lamp.   3. The direct type backlight according to claim 2, wherein a relationship of L2 ≧ 0.45P−0.5R is satisfied when a distance between the fluorescent lamp and the optical member is L2 (mm).   3. The direct portion according to claim 2, wherein the fluorescent lamp or the diffusing plate is provided with a processing portion for reducing a luminance difference between light emitting surfaces between the fluorescent lamp and the fluorescent lamp adjacent to the fluorescent lamp or the diffusion plate. Type backlight.   2. The direct type backlight according to claim 1, wherein a relationship of L2 ≧ 0.45P−0.5R is satisfied when a distance between the fluorescent lamp and the optical member is L2 (mm).   2. The direct portion according to claim 1, wherein the fluorescent lamp or the diffusing plate is provided with a processing portion for reducing a difference in luminance of a light emitting surface between the fluorescent lamp adjacent to and immediately above the fluorescent lamp. Type backlight.

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