JP5322630B2 - Lighting device - Google Patents

Abstract

PURPOSE: A lighting device is provided to inhibit the degradation of luminance at the intermediate area between linear-shaped light sources by respectively forming a prism portion and a lens unit on a first optical path change part and a second optical path change part. CONSTITUTION: A prism portion(61) of a first optical path change part(60) is arranged between a linear-shaped light source(30) and a diffusing plate(50). The prism portion is projected toward the linear-shaped light source. The first optical path change part varies the route of light from the linear-shaped light source and a reflecting plate(40). A second optical path change part(70) is arranged on the opposite side of the linear-shaped light source. A lens unit(71) is installed on the irradiating surface of the second optical path change part. The second optical path change part varies the route of the light passed the diffusing plate. The prism portion of the first optical path change part has the prism vertical angle of 55-75 degrees. The lens unit of the second optical path change part totally reflects some of the light towards the diffusing plate. The lens unit of the second optical path change part irradiates the light which passed the intermediate area of the linear-shaped light sources in the front direction.

Description

  The present invention relates to a lighting device, and more particularly to a lighting device used in a direct liquid crystal display device.

  An illumination device used for a direct type liquid crystal display device generally includes an illumination having a plurality of linear light sources arranged in parallel, a reflector, and a diffuser that diffuses light from the linear light source and the reflector. The device is used. In order to reduce the thickness of the liquid crystal display device, it is required to shorten the distance between the linear light source in the thickness direction of the lighting device and the diffusion plate or the liquid crystal panel. Further, in order to reduce the cost, it is required to increase the interval, that is, the pitch at which the plurality of linear light sources are arranged to reduce the number of lines used. As these thinnings and the arrangement pitch of the linear light sources increase, the problem that the image of the linear light source can be seen through only by the diffusion by the diffusion plate and periodic luminance unevenness occurs becomes significant. ing.

In order to suppress such luminance unevenness, there has been proposed an illuminating device in which a prism portion protruding toward the linear light source is provided in a region of the diffuser plate facing the linear light source (see Patent Document 1). ).
JP 2004-127680 A

  The illumination device described in Patent Document 1 prevents the luminance directly above the linear light source from increasing by disposing the prism portion directly above the linear light source, and suppresses uneven luminance. For this reason, the positional relationship between the linear light source and the prism portion must be strictly performed, and the light control member for manufacturing a light control member such as a diffusion plate provided with the prism portion or assembling the illumination device to the liquid crystal display device The alignment between the light source and the linear light source is complicated. In addition, since the light control member that matches the arrangement conditions (for example, the arrangement interval) of the linear light source must be manufactured, the light control member lacks versatility, which increases the manufacturing cost of the light control member. It can be a factor that causes an increase in production cost.

  Even if it matches the arrangement conditions of the linear light source, it is possible to improve the complexity of manufacturing and alignment by setting the configuration to suppress uneven brightness as versatility. It is.

  An object of the present invention is to provide an illuminating device that can improve the occurrence of periodic luminance unevenness through which an image of a linear light source can be seen with a versatile structure.

The present invention that achieves the above object is a lighting device comprising a plurality of linear light sources arranged in parallel, a reflector, and a diffuser that diffuses light from the linear light source and the reflector. A first optical path that is disposed between the linear light source and the diffusion plate and includes a prism portion that protrudes toward the linear light source, and changes a path of light from the linear light source and the reflection plate. A second light path changing unit that is disposed on the opposite side of the linear light source across the diffuser plate, has a lens unit on the exit surface, and changes the path of the light transmitted through the diffuser plate And the prism portion in the first optical path changing portion has a prism apex angle of 55 ° to 75 °, and the prism portion causes the line in the intermediate region between the linear light sources. The light from the light source is totally reflected and is reflected in the second light path changing unit. In the region facing the linear light source, a part of the transmitted light is emitted at an angle smaller than that at the time of incidence, and the remaining light is totally reflected toward the diffusion plate, and the linear light source. It is an illuminating device that emits light that has passed through in the front direction in an intermediate region between them.

  According to the present invention, the prism portion in the first optical path changing unit and the lens unit in the second optical path changing unit suppress the decrease in luminance even in the intermediate region between the linear light sources, and the linear shape. It is possible to improve the occurrence of periodic luminance unevenness through which the image of the light source can be seen.

  Further, since the first and second optical path changing units do not strictly change the shape and assembly position in accordance with the arrangement condition of the linear light source, etc., the first and second optical path changing units are generally used. Can be applied. Therefore, the occurrence of uneven brightness can be improved by a general-purpose structure, and an increase in the manufacturing cost of the first and second optical path changing units is suppressed, thereby suppressing an increase in the manufacturing cost of the lighting device. You can also.

  Furthermore, even when matching the arrangement conditions of the linear light source, etc., as a precondition, the configuration for suppressing the luminance unevenness is set with versatility, so the alignment accuracy of the member for matching is set. Since it can be set loosely, the production of the member for matching is not complicated, the increase in production cost can be suppressed, and the complexity of alignment can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram illustrating an illumination device 10 according to an embodiment of the present invention, and FIG. 2A illustrates a locus of light rays according to an embodiment including first and second optical path changing units 60 and 70. 2A and 2B are diagrams for explaining the trajectory of light rays when the second optical path changing unit 70 is not provided, and FIGS. 3A to 3D are prism units 61. It is a figure for using for description of the angle range of prism apex angle (alpha).

  With reference to FIG. 1 and FIG. 2 (A), the illuminating device 10 is arrange | positioned at the back surface of the LCD panel 20, and is used in order to illuminate the LCD panel 20. FIG. In general, the illumination device 10 includes a plurality of linear light sources 30 arranged in parallel, a reflecting plate 40, a diffusion plate 50 that diffuses light from the linear light sources 30 and the reflecting plate 40, and a first optical path. A changing unit 60 and a second optical path changing unit 70 are provided. The first light path changing unit 60 is disposed between the linear light source 30 and the diffuser plate 50, is provided with a prism unit 61 that protrudes toward the linear light source 30, and is provided from the linear light source 30 and the reflection plate 40. Is changed (see reference L1 in FIG. 2A). The second light path changing unit 70 is disposed on the opposite side of the linear light source 30 with the diffusion plate 50 interposed therebetween, and the lens unit 71 is provided on the emission surface, and changes the path of light transmitted through the diffusion plate 50. (See symbols L2 and L4 in FIG. 2A). The prism 61 in the first optical path changing unit 60 has a prism apex angle α of 55 ° to 75 °. Further, the lens unit 71 in the second optical path changing unit 70 totally reflects a part of the transmitted light in the region Wa facing the linear light source 30 toward the diffusion plate 50 (FIG. 2A). In the intermediate region Wb between the linear light sources 30, the transmitted light is emitted in the front direction (see reference L4 in FIG. 2A). In addition, the position of the boundary of the area | region Wa which opposes the linear light source 30 and the intermediate | middle area | region Wb between linear light sources 30 is that the light from the linear light source 30 and the reflecting plate 40 has faced in various directions. Therefore, it cannot be strictly specified. The position of the boundary varies depending on the arrangement interval of the plurality of linear light sources 30 and the distance between the linear light sources 30 and the first optical path changing unit 60. However, since the present invention aims to improve the generation of periodic luminance unevenness through which the image of the linear light source 30 can be seen, the region Wa facing the linear light source 30 and the linear The intermediate region Wb between the light sources 30 is naturally determined according to the specification of the lighting device 10 as a reference. Details will be described below.

  The linear light source 30 includes not only a cold cathode ray tube (CCFL) but also a light source in which dot LEDs are arranged in a line. The reflector 40 reflects the light emitted from the linear light source 30 toward the first optical path changing unit 60. The light reflected by the first optical path changing unit 60 or the like is also reflected again by the reflecting plate 40. The diffusion plate 50 is formed by containing a light diffusion material in a resin base material.

  The first optical path changing unit 60 is configured, for example, by attaching a prism sheet to the diffusion plate 50 with a transparent adhesive film. As is well known, the prism sheet is made of, for example, an ultraviolet curable resin (UV resin). The prism portion 61 protrudes toward the linear light source 30 and downward in FIG. The height and pitch of the prism portion 61 can be selected as appropriate. For example, the height is about 50 μm and the pitch is also about 50 μm. The diffusing plate 50 and the prism sheet may be integrated as illustrated, or may be separate sheets. The prism part 61 extends parallel to the longitudinal direction of the linear light source 30.

  The second optical path changing unit 70 includes, for example, a lenticular lens sheet and a microlens array sheet using the same material of the prism sheet. The pitch of the lenticular lens forming the lens unit 71 or the diameter of the microlens is, for example, about 30 to 150 μm, and is appropriately selected so as not to cause moire between the pixels of the LCD panel. The lens portion 71 extends parallel to the longitudinal direction of the linear light source 30.

  The angle range of the prism apex angle α of the prism unit 61 will be described with reference to FIG. In order to consider the incident angle of light emitted in the front direction, when light is incident vertically from the opposite direction, the light is emitted twice when the prism apex angle α is 90 ° as shown in FIG. Since the light is totally reflected and returned to the incident side, there is no light incident from the prism unit 61 side and emitted vertically. As shown in FIG. 3C, when the prism apex angle α is 80 °, the refractive index of the prism portion 61 is emitted to the light source side in a general optical plastic (1.49 to 1.6). However, the direction of the outgoing light beam is on the opposite side of the light source from the outgoing point, and no light enters the prism side and exits vertically. When the angle of the prism in which the light beam vertically incident from the reverse direction is emitted horizontally is calculated, the angle is 76.2 ° when n = 1.5, and 74.8 ° when n = 1.6. is there. As shown in FIG. 3B, when the prism apex angle α is 60 °, it is perpendicularly incident on the second surface after reflection (the right side surface in the figure), and therefore the angle of the emitted light beam with respect to the sheet surface. Is 60 °. When the prism apex angle α is narrower than that, the direction of refraction on the second surface is the thickness direction, and thus the action of raising a wide range of light vertically becomes weak. Based on the above consideration and the results of the examples described later, the prism apex angle α is preferably in the range of 55 ° to 75 °, which is slightly narrower than 60 °. More preferably, the prism apex angle α is 60 ° to 70 °.

  With reference to FIG. 2 (A), according to the illuminating device 10 of embodiment provided with the 1st and 2nd optical path change parts 60 and 70, in the intermediate | middle area | region Wb between the linear light sources 30, it is a line. Since the light from the linear light source 30 is totally reflected and directed to the observation side by the downward prism portion 61 in the drawing in the first optical path changing unit 60, the image of the linear light source 30 is observed in a wide range (L1). See). Moreover, since it injects into the lens part 71 in the 2nd optical path change part 70 at the angle near perpendicular | vertical, it permeate | transmits efficiently and radiate | emits toward a front direction (refer L4). On the other hand, in the area Wa directly above the linear light source 30, that is, in the region Wa facing the linear light source 30, the light from the linear light source 30 is divided into two parts left and right by the prism unit 61 (see L 1). Incident at an angle of ~ 50 °. Part of the light is emitted at an angle smaller than that at the time of incidence by the action of the lens unit 71 (see L2), but part of the light is totally reflected by the lens surface and returns to the diffusion plate 50 side (see L3). reference). As a result, it is possible to suppress the occurrence of periodic luminance unevenness through which the image of the linear light source 30 can be seen as compared with the case of only the diffusion plate 50.

  Since the first light path changing unit 60 is a sheet in which prism elements are arranged to direct the direction of the light beam of the linear light source 30 in a wide range in the observation direction by using total internal reflection, the first light path changing unit 60 is refracted by a lenticular lens or the like. The refractive power of the light source is larger than that using the light source, and a decrease in luminance can be suppressed even at an intermediate point (region Wb) between the linear light source 30 and the linear light source 30.

  FIG. 2B shows the ray trajectory in the region Wa directly above the linear light source 30, that is, in the region Wa when the second light path changing unit 70 is not provided. In this case, since the action of the lens unit 71 cannot be obtained, strong luminance unevenness is observed when observed from 40 ° to 50 °. Therefore, by providing the second optical path changing unit 70, it is possible to suppress the occurrence of luminance unevenness when observed from 40 ° to 50 °.

  The first and second optical path changing units 60 and 70 do not strictly change the shape or the assembling position according to the arrangement condition (for example, arrangement interval) of the linear light source 30. For this reason, even if the arrangement conditions of the linear light source 30 are changed according to the request on the side of the LCD panel 20 to be illuminated, the first and second optical path changing units 60 and 70 are applied universally. be able to. Therefore, the occurrence of uneven brightness can be improved by a versatile structure, and an increase in the manufacturing cost of the first and second optical path changing units 60 and 70 can be suppressed, thereby reducing the manufacturing cost of the lighting device 10. The increase can be suppressed.

  FIG. 4 is a schematic configuration diagram illustrating a modified example in which a reflective layer 72 is provided at a portion corresponding to the boundary of the lens unit 71 in the back surface of the second optical path changing unit 70.

  As described above, in the case of only the first optical path changing unit 60 including the prism unit 61 without providing the second optical path changing unit 70, luminance unevenness is observed when observed from an oblique direction. End up. This angle is, for example, about 40 ° when the prism apex angle α is 60 °. Therefore, it is preferable to combine with an optical element that reflects or scatters a large amount of incident light at an angle of about 40 ° or more than the vertically incident light and returns to the diffuser plate 50 side. Examples of such an optical element include a lenticular lens sheet and a microlens array sheet with the lens side facing the light output side.

  Although the back surface of the second optical path changing unit 70 shown in FIG. 1 is a flat surface, as shown in FIG. 4, the lens unit 71 of the back surface (non-lens part side) of the second optical path changing unit 70. A reflective layer 72 may be further formed at a portion corresponding to the boundary. By providing the reflective layer 72 with a certain thickness (1/10 to 1/3 of the width), oblique light is more easily shielded, and luminance unevenness when observed from an oblique direction can be eliminated. It is.

  5A and 5B are schematic configuration diagrams showing a modified example in which the tip shape of the prism unit 61 in the first optical path changing unit 60 is changed, and FIG. 5C shows adjacent prism units 61. It is a schematic block diagram which shows the example of a modification arrange | positioned through the clearance gap part.

  The tip of the prism portion 61 in the first optical path changing portion 60 may be formed flat on the flat surface 62a (FIG. 5A), or may be formed on the curved surface 62b and rounded (FIG. 5B )). Further, the adjacent prism portions 61 in the first optical path changing portion 60 may be arranged with a gap 63a therebetween, and a flat portion 63b may be formed between the prism portions 61 (FIG. 5C). .

  With this configuration, because of the light indicated by the symbol L5a and the light indicated by the symbol L5b, the omission of light when observed from an oblique direction, or the light directly above the linear light source 30 when observed from the front. The gap is also reduced. The width of the flat surface 62a and the curved surface 62b is preferably 1/6 to 1/3 of the width of the prism. A lenticular lens may be inserted in the gap 63a.

  FIG. 6 is a schematic configuration diagram showing a modified example in which the white paint 51 that reflects light is formed on the emission side of the diffusion plate 50.

  In order to alleviate the light emitted obliquely from the diffuser plate 50, the white paint 51 that is formed on the exit side of the diffuser plate 50 and reflects the transmitted light is linear in the region Wa facing the linear light source 30. It is good to form densely compared with the intermediate region Wb between the light sources 30. The white paint 51 has a shape of white dots or white stripes and is formed by printing. The density of the white paint 51 is the area of white per unit area, and “densely formed” refers to increasing the area of white per unit area.

  In forming the white paint 51, the luminance unevenness of the linear light source 30 has already been considerably reduced by the action of the prism unit 61 in the first light path changing unit 60 and the lens unit 71 in the second light path changing unit 70. Yes. For this reason, the density or density of the white paint 51 is smaller than that in which the white paint 51 is simply formed on the diffuser plate 50 that does not have the prism portion 61, and the white portion between the upper portion and the intermediate portion of the linear light source 30 is small. The difference in density (density) is small. Therefore, the alignment accuracy between the linear light source 30 and the white print pattern can be set loosely.

  In this way, even when the arrangement conditions of the linear light source 30 are met, as a premise, the configuration for suppressing the luminance unevenness is set with versatility, so that the manufacture of the diffusion plate 50 is complicated. In other words, the increase in production cost can be suppressed. Further, the complexity of alignment of the diffusion plate 50 is not reduced or caused.

  FIG. 7 is a schematic configuration diagram illustrating a modified example in which a part of the prism unit 61 in the first optical path changing unit 60 is a lenticular lens 64.

  As shown in the drawing, a lenticular lens 64 may be disposed in the region Wa of the first light path changing unit 60 facing the linear light source 30 instead of the prism unit 61. In the intermediate region Wb between the linear light sources 30, the prism portion 61 is arranged as it is.

  By configuring in this way, the gaps between light when observed obliquely and light immediately above the linear light source 30 when observed from the front are also reduced.

  Also in this case, the luminance unevenness of the linear light source 30 is already considerably reduced by the action of the prism unit 61 in the first optical path changing unit 60 and the lens unit 71 in the second optical path changing unit 70. The alignment accuracy between the light source 30 and the lenticular lens 64 can be set loosely. Even when the arrangement condition of the linear light source 30 is met, as a premise, the configuration for suppressing luminance unevenness is set with versatility, so the first optical path change for arranging the lenticular lens 64 is performed. The production of the part 60 is not complicated and an increase in production cost can be suppressed. Further, the alignment of the first optical path changing unit 60 is not complicated.

  FIG. 8 is a schematic configuration diagram showing a modified example in which the prism apex angle α ′ of a part of the prism unit 61 (prism unit 65) in the first optical path changing unit 60 is changed, and FIGS. It is a figure where it uses for description of reduced prism apex angle (alpha) '.

  As shown in FIG. 8, the prism apex angle α ′ of the prism portion 65 in the region Wa facing the linear light source 30 of the first light path changing unit 60 is set as the prism in the intermediate region Wb between the linear light sources 30. It may be smaller than the prism apex angle α of the portion 61.

  More specifically, the angle at which the light beam totally reflected by the other surface is incident in the front direction after refraction incidence is about 40 ° when the refractive index is 1.5 to 1.6. In this case, the total reflection prism enlarges the angular deviation of the incident light, so that even if the vertically incident light beam is emitted vertically, it is different from a flat surface where nothing is formed. Since the light source image is enlarged, it has a function of making it difficult to visually recognize the light source image.

  Also in this case, the luminance unevenness of the linear light source 30 is already considerably reduced by the action of the prism unit 61 in the first optical path changing unit 60 and the lens unit 71 in the second optical path changing unit 70. The positioning accuracy between the light source 30 and the prism portion 65 having a reduced prism apex angle α ′ can be set loosely. Even when the arrangement condition of the linear light source 30 is matched, as a premise, the configuration for suppressing the luminance unevenness is set with versatility, so that a part of the prism unit 61 (the prism unit 65) is configured. The manufacture of the first optical path changing unit 60 with a reduced prism apex angle α ′ is not complicated, and an increase in manufacturing cost can be suppressed. Further, the alignment of the first optical path changing unit 60 is not complicated.

  Referring to FIG. 9A, when the refractive index is n, a light beam incident vertically from below is refracted by the incident surface, then totally reflected by the slope on the opposite side, and then emitted vertically again. Satisfy the following conditions.

ncos (3φ) = cos (2φ)
Using one of the functions of the spreadsheet software, “calculation function for back-calculating a value to be substituted to derive a specific calculation result”, φ satisfying the above condition was calculated.

When n = 1.50, 1.52, 1.58, 1.60, each φ is
φ = 19.65, 19.87, 20.49, 20.68
Met. Accordingly, the prism apex angle α is about 40 °. The tip angle (prism apex angle α ′) in the region Wa facing the linear light source 30 is preferably smaller than this.

  Referring to FIG. 9B, when the tip angle is further reduced, for example, when the tip angle is set to 30 degrees, as described above, as a result of studying the incidence of light from the opposite direction, a refractive index of 1. In 5 to 1.6, the angle of light that exits without refraction only and without total reflection is only about 60 ° or more.

  FIG. 10 is a schematic configuration diagram illustrating a modified example in which a part of the prism unit 61 in the first optical path changing unit 60 is a linear Fresnel lens 66. FIG. 11A is a diagram showing a ray trajectory in the modified example shown in FIG. 10, and FIG. 11B is a diagram showing a ray trajectory relative to only the diffusion plate 50. FIG. 12 is a diagram showing lens angles in the linear Fresnel lens 66.

  As shown in FIG. 10, in a region Wa of the first light path changing unit 60 that faces the linear light source 30, instead of the prism unit 61, a linear Fresnel lens 66 faces the linear light source 30, that is, the prism unit 61. It may be arranged on the same side surface. In the intermediate region Wb between the linear light sources 30, the prism portion 61 is arranged as it is.

  With this configuration, the light from the linear light source 30 is observed almost perpendicularly to the sheet by the linear Fresnel lens 66 and the prism portion 61 in the entire area of the sheet, as compared with the contrast of the diffusion plate 50 alone. Directed to the side (see FIGS. 11A and 11B). For this reason, even if the diffusion (haze) of the diffusing plate 50 is not so strong, luminance unevenness due to the omission of the linear light source 30 image can be eliminated. Further, the diffusion (haze) can be reduced as compared with the conventional diffusion plate.

  Also in this case, the luminance unevenness of the linear light source 30 is already considerably reduced by the action of the prism unit 61 in the first optical path changing unit 60 and the lens unit 71 in the second optical path changing unit 70. The alignment accuracy between the linear light source 30 and the linear Fresnel lens 66 can be set loosely. Even when the arrangement condition of the linear light source 30 is met, as a premise, the configuration for suppressing the luminance unevenness is set with versatility, so the first optical path for arranging the linear Fresnel lens 66 is set. Production of the changing unit 60 is not complicated, and an increase in production cost can be suppressed. Further, the alignment of the first optical path changing unit 60 is not complicated.

  Referring to FIG. 12, the angle of the lens in the linear Fresnel lens 66 can be calculated by the following calculation formula of the lens angle of the known incident light Fresnel lens.

tan φ = sin θ / (n ² −cos θ)
Here, φ is the lens angle, and θ is the angle of the light beam.

  FIG. 13 is a schematic configuration diagram showing a further modification of the modification shown in FIG. 10, and FIG. 14 is a diagram showing a hybrid prism that can be used in the modification shown in FIG.

  The linear Fresnel lens 66 is not limited to the case where the linear Fresnel lens 66 is disposed on the surface facing the linear light source 30 as in the modification shown in FIG. 10, and is disposed on the surface facing the diffusion plate 50, that is, the surface opposite to the prism portion 61. May be.

  As shown by being surrounded by a two-dot chain line in FIG. 13, it is preferable that the end portion of the prism portion 61 and the end portion of the linear Fresnel lens 66 are arranged to overlap each other by several pitches. This is because the light path of the oblique light can be changed by at least one of the prism portion 61 and the linear Fresnel lens 66.

  Referring to FIG. 14, a hybrid prism described in WO02 / 027399 in which a total reflection prism and a linear Fresnel lens coexist in one pitch near the boundary between the prism portion 61 and the linear Fresnel lens 66. 67 may be used.

(Example)
Hereinafter, examples will be described, but it goes without saying that the present invention is not limited to the examples.

  One side of a 50 μm thick biaxially stretched polyester film (Cosmo Shine (registered trademark) A4300 manufactured by Toyobo Co., Ltd.) is made of a UV resin having a refractive index of 1.55 and a pitch of 50 μm and a prism apex angle of 29 °. 45 °, 55 °, 60 °, 62 °, 66 °, 69 °, 75 °, and 90 ° prism sheets were prepared.

  This prism sheet is attached to a bulk light diffusion plate having a thickness of 1.3 mm, a haze of 100%, and a transmittance of 62% (measured using a haze guard II manufactured by Toyo Seiki Seisakusho Co., Ltd.) with a transparent adhesive film. A diffusion plate was created.

  Next, a lenticular lens sheet having a pitch of 130 μm was prepared using the same material as that of the prism sheet. A white stripe was formed at a portion corresponding to the boundary portion of the lens on the flat surface side of the lenticular lens sheet.

  To a backlight unit (BLU) with a cold cathode ray tube (CCFL) interval of 30 mm, a support frame of 15 cm × 21 cm is provided so that the distance between the center of the cold cathode ray tube and the prism diffusion plate is 5 mm, 7 mm, 10 mm, and 15 mm. Four types were created.

  Nine types of prism diffusion plates and a diffusion plate not bonded with a prism sheet are placed on a support frame, and the above lenticular lens sheet is placed on the two-dimensional color luminance meter (CA manufactured by Konica Minolta Sensing Co., Ltd.). -2000) was separated by 0.5 m, and in-plane brightness unevenness was measured.

  FIG. 15 is a graph showing an example of data obtained by measuring in-plane brightness unevenness of a sample product. The horizontal axis of the graph indicates the position coordinates in the arrangement direction of the cold cathode ray tubes, and the vertical axis indicates the luminance. The measurement data before correction (line La in FIG. 15) is brighter at the center and darker at the periphery. The measurement data itself was approximated to a quadratic curve, and the original data was corrected so that the approximate curve was flattened at the maximum value. A line Lb in FIG. 15 indicates an approximate curve for correction, and a line Lc indicates data after correction. FIG. 15 shows a state of correction in the case of a diffusion plate in which a prism sheet having a large change in brightness is not bonded. The corrected data is a trigonometric function with a period of 30 mm.

  Table 1 below shows the results of calculating the ratio of the average of the local minimum to the average of the local maximum of the waveform based on the corrected data.

  The closer the value of the ratio is to 1, the less the luminance unevenness of the light source is observed. In the comparison by visual observation, the luminance unevenness is considerably improved when the value is 0.82 or more, the luminance unevenness is further improved when the value is 0.9 or more, and the luminance unevenness becomes difficult to be visually recognized. There was almost nothing to do.

  From the experimental results shown in Table 1, when the distance between the center of the cold cathode ray tube and the prism diffusion plate is in the range of 5 mm to 15 mm, the effect of suppressing the occurrence of luminance unevenness is obtained when the prism apex angle is 55 ° to 75 °. It was found that the prism apex angle is particularly effective when the prism apex angle is 60 ° to 70 °.

  When the apex angle of the prism is 55 ° to 75 °, luminance unevenness was not observed even in the visual observation from an oblique direction.

  The state where the upper lenticular lens sheet was removed was also observed. As a result of visual observation from an oblique direction, even though the prism apex angle was 55 ° to 75 °, some luminance unevenness was observed although it was weak.

  From the above embodiments, the first and second light path changing units 60 and 70 in the lighting device 10 of the present invention can improve the occurrence of periodic luminance unevenness through which the image of the linear light source 30 can be seen. It was confirmed.

It is a schematic block diagram which shows the illuminating device which concerns on embodiment of this invention. FIG. 2A is a diagram for explaining the trajectory of the light beam according to the embodiment including the first and second optical path changing units, and FIG. 2B is not provided with the second optical path changing unit. It is a figure for demonstrating the locus | trajectory of the light ray in a case. FIGS. 3A to 3D are diagrams for explaining the angle range of the prism apex angle of the prism portion. It is a schematic block diagram which shows the modification which provided the reflection layer in the site | part corresponding to the boundary of a lens part among the back surfaces of a 2nd optical path change part. 5A and 5B are schematic configuration diagrams showing a modified example in which the shape of the tip of the prism portion in the first optical path changing unit is changed, and FIG. 5C is a diagram illustrating a gap portion between adjacent prism portions. It is a schematic block diagram which shows the modified example arrange | positioned spaced apart. It is a schematic block diagram which shows the modification which formed the white paint which reflects light in the output side of the diffusion plate. It is a schematic block diagram which shows the modified example which used a part of prism part in the 1st optical path change part as the lenticular lens. It is a schematic block diagram which shows the modification which changed the prism apex angle of a part of prism part in the 1st optical path change part. FIGS. 9A and 9B are diagrams for explaining a reduced prism apex angle. It is a schematic block diagram which shows the modified example which used a part of prism part in the 1st optical path change part as the linear Fresnel lens. FIG. 11A is a diagram showing a ray trajectory in the modified example shown in FIG. 10, and FIG. 11B is a diagram showing a ray trajectory in comparison with only the diffusion plate. It is a figure which shows the angle of the lens in a linear Fresnel lens. It is a schematic block diagram which shows the further modification of the modification shown by FIG. It is a figure which shows the hybrid prism which can be used in the modification shown by FIG. It is a graph which shows an example of the data which measured the brightness nonuniformity in the surface of a sample goods.

Explanation of symbols

10 Lighting device,
20 LCD panel,
30 linear light source,
40 reflector,
50 diffuser,
51 white paint,
60 1st optical path changing part,
61 Prism part,
62a flat surface,
62b curved surface,
63a gap,
63b flat part,
64 lenticular lens,
65 Prism part of prism apex angle α ′,
64 lenticular lens,
66 linear Fresnel lens,
67 Hybrid prism,
70 a second optical path changing unit,
71 Lens section,
72 reflective layer,
α, α ′ Prism apex angle (α> α ′),
Wa The area facing the linear light source,
Wb Intermediate region between linear light sources.

Claims (8)

A lighting device comprising a plurality of linear light sources arranged in parallel, a reflector, and a diffuser that diffuses light from the linear light source and the reflector,
A first light that is disposed between the linear light source and the diffuser plate, has a prism portion that protrudes toward the linear light source, and changes a path of light from the linear light source and the reflecting plate. A route change unit;
A second optical path changing unit that is disposed on the opposite side of the linear light source with the diffusion plate interposed therebetween, has a lens portion provided on the exit surface, and changes a path of light transmitted through the diffusion plate. And
The prism portion in the first light path changing portion has a prism apex angle of 55 ° to 75 °, and the prism portion allows light from the linear light source to be emitted in an intermediate region between the linear light sources. Total reflection
The lens unit in the second light path changing unit emits a part of the transmitted light in a region facing the linear light source at an angle smaller than that at the time of incidence, and the remaining light is directed to the diffusion plate side. An illuminating device that emits light that is totally reflected and transmitted in an intermediate region between the linear light sources in a front direction.   The lighting device according to claim 1, further comprising a reflective layer provided at a portion corresponding to a boundary of the lens portion in the back surface of the second light path changing portion.   The illumination device according to claim 1, wherein a tip of the prism portion in the first optical path changing unit is formed to be a flat surface or a curved surface.   The lighting device according to any one of claims 1 to 3, wherein adjacent prism portions in the first optical path changing unit are arranged with a gap portion therebetween.   The white paint that is formed on the emission side of the diffusion plate and reflects the transmitted light is formed denser in an area facing the linear light sources than in an intermediate area between the linear light sources. The lighting device according to any one of claims 1 to 4.   The illumination according to any one of claims 1 to 5, wherein a lenticular lens is disposed in place of the prism portion in a region facing the linear light source of the first light path changing portion. apparatus.   The prism apex angle of the prism unit in the region facing the linear light source of the first optical path changing unit is made smaller than the prism apex angle of the prism unit in the intermediate region between the linear light sources. The lighting device according to any one of claims 1 to 5.   In the region facing the linear light source of the first light path changing unit, instead of the prism unit, a linear Fresnel lens is arranged on a surface facing the linear light source or a surface facing the diffusion plate, The lighting device according to any one of claims 1 to 5.

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