JP2005310594A - Lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve light utilization efficiency in a side light type lighting system to realize a high-luminance, thin and lightweight lighting system. <P>SOLUTION: A directional scattering sheet for scattering light at a predetermined incident angle and transmitting light other than it is disposed in a space between a light source and a light entering surface of a light guide plate; and a columnar lens sheet is used for the directional scattering sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lighting device used in a liquid crystal display device used in a timepiece, a mobile phone, an audio, an electronic device, and the like.

  In recent years, liquid crystal display devices having a thin and light feature have been widely used for portable devices and information devices. However, since the liquid crystal display device is a light-receiving type, an illuminating device is often installed on the front or back surface of the liquid crystal display element for the purpose of displaying a bright and high-definition image.

In order to realize the thin and light nature inherent to this liquid crystal display device, a sidelight type illumination device in which LEDs are arranged on the side surfaces of a light guide plate as a light source is frequently used (Patent Document 1).
Patent No. 3301752 (page 3, Fig. 1)

  However, the sidelight type illumination device radiates light from the light source with the highest light emission luminance in order to perform illumination by controlling the light reflected and guided inside the light guide plate by a prism or the like to leak outside. Light having a small angle has a problem that the utilization efficiency is low, for example, the number of multiple reflections is small and the light is emitted from the end face of the light guide plate.

  In the illumination device of the present invention, a directional scattering sheet that scatters light of a predetermined incident angle and transmits other light is disposed in a gap between the light source and the light incident surface of the light guide plate. The light having a small emission angle can be scattered and introduced into the inside of the light guide plate, and an illumination device with high light utilization efficiency can be obtained.

  According to the present invention, it is possible to provide a thin and light liquid crystal display device having a simple structure and high brightness, and therefore, it is possible to realize further increase in brightness and weight reduction of information equipment using these liquid crystal display devices. Have

  The illuminating device of the present invention includes a light source, a transparent light guide plate, directional scattering that scatters light of a predetermined incident angle and transmits other light between the light incident surface of the light guide plate and the light source. With layers.

  Here, as the directional scattering layer, a plurality of fine columnar structures are arranged in the plane, and the columnar central region of the columnar structure is formed with a higher refractive index than the outer peripheral region surrounding the columnar structure, and light is emitted in the thickness direction. It was decided to use a columnar lens sheet having a function of guiding. Furthermore, the columnar structure constituting the columnar lens sheet was set so as to be oriented substantially vertically in the surface of the columnar lens sheet. Here, the scattering angle of the columnar lens sheet was set to approximately 10 to 45 degrees.

  In addition, a prism having a ridge line in a direction substantially perpendicular to the light irradiation surface of the light guide plate is formed on the light incident surface of the light guide plate. Further, the lens sheet was formed by bonding to the light incident surface of the light guide plate.

  Embodiments of the lighting device of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows a cross-sectional view of the illumination device of this embodiment. A light source 1 is disposed on the light incident end face side of the light guide plate 2. A columnar lens sheet 3 as a directional scattering sheet is disposed on the light incident surface. As the light source 1, a cold cathode tube or an LED light source can be used, but it is preferable to use an LED light source that has high luminous efficiency and is suitable for downsizing. As this LED light source, it is desirable to use a so-called white LED light source that obtains green light by converting the wavelength of blue light from a blue LED light source with a yellow phosphor to obtain green light and mixing the original blue light with the green light. . Further, it is desirable to use the white LED light source and the red LED light source in combination to make the mixed color light closer to white. Moreover, although only one light source 1 is drawn in the drawing, three to five light sources 1 are usually arranged.

  The light guide plate 2 is made of a transparent polymer material. Specifically, it is formed of a polymer material such as an acrylic resin, a polycarbonate resin, or a cycloolefin resin. The light guide plate 2 can be easily manufactured by injection molding using these materials. The columnar lens sheet 2 has a plurality of fine columnar structures arranged in a plane, and the columnar central region of the columnar structure is formed with a higher refractive index than the outer peripheral region surrounding the columnar structure, and guides light in the thickness direction. It has a function. That is, a graded index columnar lens whose refractive index continuously increases toward the center, or a step index having a two-layer structure in which the refractive index of the central portion is higher than the refractive index of the outer peripheral region surrounding it. It has a film structure in which a plurality of mold columnar lenses are arranged in a plane. The columnar lens sheet is manufactured by, for example, irradiating a liquid reaction layer made of two or more kinds of photopolymerizable compounds having different refractive indexes with ultraviolet rays through a gradation-processed photomask, thereby depending on the light irradiation intensity. The refractive index distribution is controlled by controlling the difference in the photopolymerization rate of the photopolymerizable compound.

  FIG. 2 shows another configuration relating to the illumination device of the present invention. 2 is different from FIG. 1 in that the columnar lens sheet 3 is bonded to the light incident surface of the light guide plate 2. As described above, by joining the columnar lens sheet 3 to the light irradiation surface of the light guide plate 2, the position of the columnar lens sheet 3 and the light guide plate 2 is fixed even if a mechanical force acts on the lighting device. Therefore, stable characteristics can be obtained. Moreover, since the reflectance at the incident surfaces of the columnar lens sheet 3 and the light guide plate 2 can be reduced, the light utilization efficiency is improved.

  In FIG. 1 and FIG. 2, the component having a small radiation angle in the light emitted from the light source 1 is scattered by the columnar lens sheet 3, and the component having a large radiation angle is linearly transmitted through the columnar lens sheet 3 to be guided. It propagates while repeating multiple reflections inside the optical plate 2. Concavities and convexities such as prism groups and fine scattering structures are formed according to a predetermined rule on the light irradiation surface of the light guide plate 2 or on the opposite surface thereof. Illuminate in a plane by deflecting.

  Next, the behavior of light in the columnar lens sheet 3 will be described. FIG. 5 is a schematic diagram showing the behavior of light when a step index type columnar lens sheet is used. In the figure, typical optical paths of light incident on the columnar lens sheet 3 from the light source 1 are indicated by arrows 22, 23 and 24. The light from the light source 1 is incident on the columnar lens sheet 3 with various incident angles, and the range has a component of 0 degree to about 90 degrees. In the step index type columnar lens sheet, the high refractive index region 10 and the low refractive index region 11 are formed with a clear boundary.

  First, the light indicated by the arrow 22 will be described. This light shows a case where the incident angle with respect to the surface of the columnar lens sheet 3 is small. The light incident on the columnar lens sheet 3 from the light source 1 is refracted toward the normal side of the light incident surface of the light guide plate according to Snell's law. The light incident on the high refractive index region 10 is incident on the boundary surface with the low refractive index region 11, but since the incident angle on the boundary surface is larger than the critical angle, it is totally reflected on the boundary surface. . This light is repeatedly reflected at the boundary surface between the high refractive index region 10 and the low refractive index region 11 and guided to the light incident surface side of the light guide plate, and is emitted from the light guide plate side surface of the columnar lens sheet. .

  At this time, the light emission direction from the columnar lens sheet is determined by the layer thickness of the columnar lens sheet, the incident angle and the incident position of the light to the high refractive index region 10. For example, the light indicated by the arrow 23 has the same incident angle as the light indicated by the arrow 22, but the incident position is different. FIG. 5 shows a case where the light indicated by the arrow 23 is directly reflected on the surface on the light guide plate side without being reflected by the boundary surface between the high refractive index region 10 and the low refractive index region 11. Since this light is incident on the surface of the light guide plate at an incident angle different from that indicated by the arrow 22, the angle emitted from the columnar lens sheet is completely different from that indicated by the arrow 22. When the layer thickness of the columnar lens sheet is increased, the number of reflections at the boundary surface is increased, so that the difference in the emission angle depending on the incident position becomes more remarkable. Also, in the graded index type columnar lens sheet, the propagation of light in the columnar lens tends to bend continuously toward the higher refractive index, so the emission angle has a uniform distribution within a certain angle range. To have. In this way, light within an angle of incidence with respect to the columnar lens sheet behaves as if it is scattered.

  The scattering angle increases as the refractive index difference between the high refractive index region 10 and the low refractive index region 11 increases. The scattering angle is limited to a specific range. Therefore, the columnar lens sheet behaves as a directional scattering sheet. Furthermore, the haze value increases as the layer thickness of the columnar lens sheet increases, as the column radius decreases, and as the number density of columnar lenses in the sheet plane increases.

  In the illumination device of the present embodiment, a columnar lens sheet having a columnar lens with a lens diameter of 0.2 μm to 250 μm and a lens height (columnar lens sheet layer thickness) of 10 μm to 200 μm can be used. However, considering the production yield, light utilization efficiency, ease of handling, etc., it is preferable that the lens diameter is 0.5 μm to 100 μm and the lens height is 20 μm to 80 μm. In addition, a columnar lens having a refractive index difference of 0.01 to 0.05 can be used.

  Next, the behavior of light that has entered the high refractive index region 10 from the light source 1 at a larger incident angle is indicated by an arrow 23. In this case, the incident angle of light incident on the boundary surface between the high refractive index region 10 and the low refractive index region 11 is smaller than that of the light indicated by the arrow 22. As a result, the light passes through the boundary surface, passes through the low refractive index region 11 side, and is emitted from the opposite surface as if passing through a transparent sheet on which no columnar lens is formed.

  Thus, the angle of light incident on the high refractive index region 10 determines whether the light emitted from the opposite surface is scattered or transmitted linearly. An angle range in which light incident on the columnar lens sheet is scattered is referred to as a scattering incident angle, and an angle range in which light is transmitted linearly is referred to as a linear transmission angle.

  Next, the behavior of light in the graded index columnar lens sheet is shown. A graded index type columnar lens has a high refractive index region near the center of the columnar shape, and its outer periphery is a low refractive index region. However, like a step index type columnar lens, a high refractive index region and a low refractive index region There is no clear interface between them.

  Light incident on the inside of the graded index columnar lens bends the optical path toward a higher refractive index. Therefore, the optical path in this columnar lens shows a smooth curve. However, in this case as well, as in the case of the step index type columnar lens, there are a scattering incident angle and a linear transmission angle. That is, the light incident at the scattering incident angle is guided through the columnar lens and scattered and emitted from the surface of the columnar lens sheet, but the light incident at the linear transmission angle is transmitted without being scattered by the columnar lens sheet.

  At this time, as in the case of the step index type columnar lens sheet, the emission direction of the specific light from the columnar lens sheet is determined by the layer thickness of the columnar lens sheet, the incident angle of light to the columnar lens, and the incident position. And it is radiate | emitted so that the bias | inclination of a scattering direction may become so small that the layer thickness of a columnar lens sheet | seat becomes thick. In addition, the scattering angle increases as the gradient of the refractive index formed by the high refractive index region and the low refractive index region increases.

  FIG. 6 shows the light transmission characteristics of the columnar lens sheet used in the present invention. In FIG. 6, the horizontal axis represents the incident angle to the columnar lens sheet, and the vertical axis represents the light transmission intensity for each incident angle. However, the measurement was performed in the atmosphere with a columnar lens sheet attached to a transparent glass substrate. As can be seen from FIG. 6, the columnar lens sheet is found to have almost zero light intensity at the angle α. When the incident angle is within the range of -α to α, the light is scattered after transmission, and when the absolute value of the incident angle is greater than or equal to α, the light is transmitted without being scattered. That is, α represents the upper limit of the scattering incident angle.

  The value of α can be controlled to an arbitrary value of about 10 to 45 degrees by adjusting the layer thickness of the columnar lens sheet, the aperture of the columnar lens, or the difference in refractive index of the columnar lens. That is, light that has entered the columnar lens sheet at a scattering incident angle of 10 to 45 degrees or less can be scattered with a scattering angle of 10 to 45 degrees. By doing so, the spread angle of the component having a small radiation angle in the light emitted from the light source can be increased, and the light can be efficiently reflected by multiple reflections within the light guide plate 2. Become. In addition, with respect to components that have been incident with light having a scattering incident angle or more, the light is transmitted linearly, so that the same effect as that of a conventional illumination device can be obtained. In order to effectively multiple-reflect light within the light guide plate, it is preferable to use a light having a scattering incident angle as large as possible.

  In addition, a prism having a ridge line in a direction substantially perpendicular to the light irradiation surface of the light guide plate 2 can be formed on the light incident surface of the light guide plate 2. This prism is a convex prism on the surface having an apex angle of approximately 90 to 135 degrees and a height of 100 to 200 μm, and the light from the light source 1 is spread in the longitudinal direction of the light incident surface so as to be inside the light guide plate 2. Have the effect of guiding light uniformly.

  The prism formed on the light irradiation surface of the light guide plate 2 is not always necessary when the light source 1 includes a lens having the same function.

  FIG. 3 schematically shows a cross-sectional view for explaining the behavior of light on the light incident surface of the illumination device of the present invention. In FIG. 3, an optical path of light having a small emission angle from the light source 1 is indicated by an arrow 20, and an optical path of light having a large emission angle is indicated by an arrow 21. As described above, the light 20 having a small radiation angle from the light source 1 enters the columnar lens sheet 3 within the range of the scattering incident angle, and thus scatters and enters the light guide plate 2. Since this scattering angle is 45 degrees or less, even when the columnar lens sheet 3 is bonded to the light guide plate 2 as shown in FIG. 2, the light irradiation surface of the light guide plate and its opposite surface It is incident at an angle of incidence greater than the critical angle, and multiple reflections are efficiently performed inside.

  On the other hand, the light 21 having a large radiation angle from the light source 1 is incident in accordance with Snell's law as in the case of a normal light guide plate from the light guide plate entrance surface. Is done.

  FIG. 4 schematically shows a cross-sectional view illustrating a general configuration of a liquid crystal display device using the illumination device of the present invention. The illuminating device of the present invention can have the same configuration as a normal sidelight type illuminating device except that the columnar lens sheet 3 is arranged on the light incident surface of the light guide plate 2. A prism structure or a fine scattering structure is formed on the light irradiation surface of the light guide plate 2 or on the surface facing the light guide plate 2 so as to deflect the light path of the light that is internally reflected and guided to be extracted from the light irradiation surface. A liquid crystal panel 7 is disposed directly above the light irradiation surface side of the light guide plate 2 via a prism sheet 9. In addition, in the gap between the housing 6 for supporting the light source 1 and the light guide plate 2 and the light guide plate 2, the light leaking outside from the light guide plate 2 is returned to the inside of the light guide plate 2 and reused. Reflectors 4 and 5 are arranged. The reflectors 4 and 5 may be omitted when a white polymer material having a high reflectance is used as a material for forming the casing 6.

  The prism sheet 9 is a transparent sheet formed on the surface of the light guide plate 2 and having a ridge line formed on the surface thereof and a prism group formed substantially parallel to the light incident surface of the light guide plate 2. It is intended to be used efficiently by raising it vertically. In the figure, only one prism sheet 9 is depicted, but two sheets having prism ridge lines that are orthogonal to each other may be used in an overlapping manner.

  Further, a diffusion plate may be disposed in the gap between the light guide plate 2 and the prism sheet 9.

Specific examples of the present invention will be described below.
(Concrete example)
The lighting device shown in FIG. 1 was produced. The size of the light guide plate was 35 mm × 43 mm × 0.6 mm. Three white LED light sources as light sources were arranged on the light incident surface of the light guide plate. In addition, a columnar lens sheet having an alignment direction of the columnar lens substantially perpendicular to the surface and a scattering angle of 45 degrees is disposed on the light incident surface of the light guide plate. The thickness of the columnar lens sheet was 70 μm, and the columnar lens diameter was 30 μm. On the surface of the light guide plate 2 facing the light irradiation surface, a prism having ridge lines formed perpendicular to the arrangement direction of the light sources was formed. The apex angle of this prism was 90 degrees, and the elevation angle on the light source side was 30 degrees. Further, the pitch of the prism was changed from the light source side in a quadratic function, the pitch on the light source side was 250 μm, and the pitch at the end on the side facing the light source was 20 μm. For comparison, an ordinary lighting device having the same configuration and having no columnar lens sheet on the light incident surface of the light guide plate was prepared. When the luminance of these illuminating devices was measured, it was found that the maximum luminance of the illuminating device according to the present invention was about 12% larger than that of a normal illuminating device.

It is sectional drawing which shows typically the illuminating device by this invention. It is sectional drawing which shows typically the illuminating device by this invention. It is sectional drawing which shows typically an example of the optical path of the illuminating device by this invention. It is sectional drawing which shows typically the liquid crystal display device using the illuminating device by this invention. It is sectional drawing which shows typically the optical path in the columnar lens sheet used for this invention. It is a graph which shows the light transmission characteristic of the columnar lens sheet used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LED light source 2 Light-guide plate 3 Columnar lens sheet 4, 5 Reflector 6 Housing 7 Liquid crystal panel 8 Prism sheet 10 High refractive index layer 11 Low refractive index layer

Claims (5)

  A light source, a transparent light guide plate, and a directional scattering layer that scatters light at a predetermined incident angle and transmits other light between the light incident surface of the light guide plate and the light source. A lighting device characterized by the above.   The directional scattering layer includes a plurality of fine columnar structures arranged in a plane, and the columnar central region of the columnar structure is formed with a higher refractive index than the outer peripheral region surrounding the columnar structure, and guides light in the thickness direction. It is a columnar lens sheet which has a function, The illuminating device of Claim 1 characterized by the above-mentioned.   The lighting device according to claim 2, wherein the columnar structure constituting the columnar lens sheet is oriented substantially perpendicularly within the surface of the columnar lens sheet.   The lighting device according to claim 2 or 3, wherein a scattering angle of the columnar lens sheet is approximately 10 to 45 degrees.   The illumination according to claim 1, wherein a prism having a ridge line in a direction substantially perpendicular to the light irradiation surface of the light guide plate is formed on the light incident surface of the light guide plate. apparatus.

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