JP2005078909A - Surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device in which irregular distribution of luminance can be reduced by a simple structure. <P>SOLUTION: The light source device comprises a planar light guide plate 1, a LED unit 3 having a plurality of LEDs 31 arranged at the light incidence face of the light guide plate 1, and an optical element 2 located at the part where a diffraction pattern 21, generating diffraction light mainly in 0th and ±1st direction, and the LED face each other. The optical element 2 is arranged between the incidence face of the light guide plate 1 and the LED unit 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface light source device, for example, a surface light source device suitable for use as a backlight or a front light of a liquid crystal display device provided in a mobile phone or the like.

  In recent years, technologies for reducing the weight, size, and power consumption of electronic devices have been remarkably developed. In mobile phones and portable information terminal devices (PDAs), a liquid crystal display device is used as a display device, and weight reduction, size reduction, and low power consumption have been achieved.

  There are transmissive and reflective liquid crystal display devices. The transmissive liquid crystal display device is provided with an illuminating device that illuminates the liquid crystal display panel from the back side, so-called backlight, and the reflective liquid crystal display device An illuminating device that illuminates the liquid crystal panel from the surface side, that is, a so-called front light is provided.

  These illuminating devices include a linear light source or a point light source, and a planar light guide plate that emits light from the linear light source or the point light source from one end surface, and is dispersed and emitted in a plane from either one of the front and back surfaces. Are known. Such surface light source devices include a type in which the light guide plate is formed with a substantially uniform plate thickness and a type in which the thickness of the light guide plate is gradually reduced as the distance from the linear light source increases.

  In recent years, in the above-described surface light source device from the viewpoint of reducing power consumption, a point light source including a light emitting diode (LED) instead of a cold cathode ray lamp has attracted attention and has been put into practical use.

  However, when using LEDs compared to a cold cathode ray lamp, a plurality of LEDs will be arranged on one end surface of the planar light guide plate, and in the vicinity of the LEDs, the front part of the LEDs is bright, and between the LEDs becomes dark, There has been a problem that light and darkness occurs in the luminance.

In order to solve this drawback, a method has been proposed in which a concave portion or a fine shape is provided on the light incident surface of the light guide plate at the front part of the LED to widen the directivity of the LED (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 10-260404

  However, even if the above-described method is used, there is a problem in that the brightness of the light emission luminance cannot be sufficiently eliminated and luminance spots are generated.

  Therefore, an object of the present invention is to provide a surface light source device that reduces luminance unevenness with a simple configuration.

  According to the present invention, in a surface light source device in which a plurality of point light sources are arranged close to a light incident surface of a planar light guide plate, a diffraction pattern that mainly generates diffracted light in the 0th order and ± 1st order directions is at least the point light source. The optical element provided at the opposite location is disposed between the light incident surface of the light guide plate and a point light source.

  When a white diode is used as the point light source, the pitch of the diffraction pattern may be set to 450 to 500 nm.

  In this invention, by arranging an optical element having a diffraction pattern between the light guide plate and the point light source, light is guided between the point light source and the point light source. It is possible to reduce the luminance spots.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing a surface light source device according to an embodiment of the present invention, and FIG. 2 is a plan view seen from the light emitting surface side of the light guide plate.

  As shown in FIGS. 1 and 2, the surface light source device of this embodiment includes an LED unit 3 in which white LEDs 31 as a plurality of point light sources are mounted on a substrate on the light incident surface side of a planar light guide plate 1. Be placed. A reflector 4 for reflecting light to the light incident surface of the light guide plate 1 is disposed so as to surround the light guide plate 1 and the LED unit 3. Between the light guide plate 1 and the LED unit 3, an optical element 2 having a diffraction pattern described later is disposed.

  The light guide plate 1, the optical element 2, the LED unit 3, and the reflector 4 are incorporated in the holder 5. A reflection sheet member is provided on the inner surface of the holder 5 to increase the light utilization efficiency as necessary.

  A liquid crystal display panel (not shown) is installed on the light exit surface side of the surface light source device.

  The light guide plate 1 is a member formed of a light-transmitting resin such as acrylic (PMMA) or polycarbonate (PC) in a wedge shape by an injection molding method. If necessary, the light guide plate 1 is provided with wrinkles (small unevenness) as a light scattering pattern on the light output surface side, the reflection surface, or both surfaces.

  The optical element 2 is a flat plate or sheet-like member on which a pitch-shaped diffraction pattern 21 corresponding to a light source wavelength used on a surface near the LED 31 is formed. This diffraction pattern 21 mainly generates diffracted light in the 0th order and ± 1st order directions. For this reason, the light emitted from the LED 31 is transmitted in the 0th-order direction by the diffraction pattern 21 and is dispersed in the primary direction by about 5 to 10%. The dispersed light is guided from the optical element 3 to the LEDs 31 and 31. Thus, by dispersing the light, the light is guided between the LED 31 and the region where the light is not guided, and the luminance unevenness is reduced.

  3A and 3B show an optical element and an LED unit part used in the present invention, FIG. 3A is a schematic diagram showing an arrangement relationship, and FIG. 3B shows a single light incident perpendicularly from the LED 31 to the optical element 2. It is a schematic diagram which shows the example tracked. In the optical element 2 shown in FIG. 3, a diffraction pattern 21 having a pitch shape corresponding to the wavelength of the light source used on the surface near the LED 31 is formed, and the pattern 22 is also located between the LEDs on the light emitting side. Is provided. The pattern 22 may be the same as the diffraction pattern 21 or the pattern pitch may be increased.

  As shown in FIG. 3B, the zero-order light passes straight through the optical element 2, but the first-order light is greatly diffracted, totally reflected in the optical element 2, and guided. And it is radiated | emitted outside in the part of the pattern 22. FIG. If the diffraction pattern 21 and the diffraction pattern 22 have the same pitch, the primary light is also emitted in parallel with the zero-order light as shown in FIG.

  The pattern 22 does not need to be the same as the diffraction pattern 21 because the guided light is extracted outside. The pattern is not limited to the diffraction pattern, and may be a satin pattern from which light is extracted.

  4A and 4B are enlarged schematic views of the pattern portion. FIG. 4A shows a concavo-convex pattern as a diffraction pattern, and FIG. 4B shows an antireflection cone pattern. In the pattern shape shown in FIG. 4A, the pattern formed a grating pattern 21 having a pitch p = 450 nm, a height h = 700 nm, and a grating width w = 225 nm, and simulated the diffracted light. The simulation result is shown in FIG. In FIG. 6, the black triangle indicates the transmittance in the zeroth direction, the black square indicates the transmittance in the primary direction, and the black rhombus indicates the transmittance in the secondary direction. As shown in FIG. 6, it is understood that there is no transmission of light in the secondary direction, and 5 to 10% light power can be dispersed in the primary direction with respect to the primary direction for wavelengths from 450 nm to 550 nm.

  In the pattern shape shown in FIG. 4A, the pattern formed a grating pattern 21 having a pitch p = 550 nm, a height h = 700 nm, and a grating width w = 225 nm, and simulated the diffracted light. The simulation result is shown in FIG. In FIG. 7, the black triangle indicates the transmittance in the zeroth direction, the black square indicates the transmittance in the primary direction, and the black rhombus indicates the transmittance in the secondary direction. As shown in FIG. 7, there is no transmission of light in the secondary direction, and it can be seen that 5 to 10% light power can be dispersed in the primary direction with respect to the primary direction for wavelengths from 400 nm to 680 nm. However, in this case, light having a wavelength of 550 nm or less is not totally reflected.

    In the pattern shape shown in FIG. 4A, the pattern formed a grating pattern 21 having a pitch p = 350 nm, a height h = 700 nm, and a grating width w = 225 nm, and simulated the diffracted light. The simulation result is shown in FIG. In FIG. 8, the black triangle indicates the transmittance in the zeroth direction, and the black square indicates the transmittance in the primary direction. As shown in FIG. 8, this pattern pitch cannot disperse light well. 6 to 8, the primary direction is the + 1st order direction, and similarly, light is dispersed in the -1st order direction.

  The dispersion ratio of the optical power can be adjusted by the pitch, height, and grating width of the grating. However, the pitch needs to be set in accordance with the type of the LED 31 to be used in order to cause ± 1st-order diffracted light to be totally reflected inside the optical element 2 and to guide the inside of the optical element 2. In the case of a white LED, the pitch may be 450 to 500 nm.

  Thus, by providing the optical element 2 of the present invention, light is incident on the light guide plate 1 from the LEDs 31 and 31, and the light is also guided to the conventional dark portion, and luminance spots are generated. Improved.

  FIG. 5 is a schematic view showing another example of the optical element and LED unit used in the present invention. FIG. 5A shows a diffraction pattern 23 provided between the diffraction patterns 21 and 21. The first-order light reflected from the exit surface side of the optical element 2 is diffracted by the diffraction pattern 23 in the 0th-order direction and emitted. 5 (a) has no pattern surface on the light emitting side of the optical element 2, so that the thickness of the optical element 2 is made slightly thicker than that shown in FIG. Yes.

  In FIG. 5B, a diffraction pattern 23 is provided between the diffraction patterns 21 and 21, and a light diffraction pattern 24 is further provided on the light emission side of the diffraction pattern 23. It has a structure that changes.

  FIG. 5C shows a case where a diffraction pattern 25 is provided on the entire surface of the optical element 2, and FIG. 5D shows a case where a reflection coat 26 is applied to the end face of the optical element 2.

  It is also possible to apply a reflective coating to the substrate surface of the LED unit 3 so that the light reflected from the optical element 2 is returned to the optical element 2 side, thereby improving the light utilization rate.

  FIG. 9 is an exploded perspective view showing a surface light source device according to another embodiment of the present invention, and this embodiment is reflected on the light incident surface of the light guide plate 1 in order to prevent a decrease in light use efficiency. The prevention structure 11 is formed. The antireflection structure 11 has a triangular cross section as shown in FIG. The pitch is preferably smaller than the wavelength of the light used, and is preferably about 250 to 350 nm. About height, what is necessary is just to make it comparable as a pitch. The structure may be one-dimensional or two-dimensional.

  In addition to the diffraction pattern and pattern portion of the optical element 2, a similar antireflection structure may be provided.

It is a disassembled perspective view which shows the surface light source device concerning embodiment of this invention. It is the top view seen from the light-projection surface side of the light-guide plate of the surface light source device concerning embodiment of this invention. The optical element used for this invention and an LED unit part are shown, (a) is a schematic diagram which shows arrangement | positioning relationship, (b) shows the example which tracked one light perpendicularly incident on the optical element from LED. It is a schematic diagram. It is the enlarged schematic diagram of a pattern part, (a) is the uneven | corrugated pattern of a diffraction pattern, (b) is the cone-shaped pattern for reflection prevention. It is a schematic diagram which shows an optical element and LED unit part of the other example used for this invention. In the pattern shape shown in FIG. 4A, the pattern forms a grating pattern having a pitch p = 450 nm, a height h = 700 nm, and a grating width w = 225 nm, and shows a simulation result of the diffracted light. In the pattern shape shown in FIG. 4A, the pattern is a diagram showing a simulation result of the diffracted light of light by forming a lattice pattern having a pitch p = 550 nm, a height h = 700 nm, and a lattice width w = 225 nm. In the pattern shape shown in FIG. 4A, the pattern forms a lattice pattern having a pitch p = 350 nm, a height h = 700 nm, and a lattice width w = 225 nm, and shows a simulation result of the diffracted light. It is a disassembled perspective view which shows the surface light source device concerning other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Optical element 3 LED unit 21 Diffraction pattern 31 LED

Claims (2)

In a surface light source device in which a plurality of point light sources are arranged close to a light incident surface of a planar light guide plate, a diffraction pattern that mainly generates diffracted light in the 0th order and ± 1st order directions is at least at a location facing the point light source. A surface light source device, wherein the provided optical element is disposed between a light incident surface of the light guide plate and a point light source. 2. The surface light source device according to claim 1, wherein a white diode is used as the point light source, and a pitch of the diffraction pattern is set to 450 to 500 nm.

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