JP2006134750A - Backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight which makes uniformity in luminance on a light emitting surface higher, reduces a loss of light, and is large in the effective area of the light emitting surface. <P>SOLUTION: A light guide plate 1 of translucence has a light entrance surface 11, from which light is introduced, on the end surface; reflection surfaces 12 to 15 which reflect the introduced light; and a light emission surface 16, from prism units 161 of which the introduced light is emitted, where the prism unit 161 has a ridgeline intersecting the light entrance surface 11 almost at a right angle, and a plurality of the prism units 161 are formed on the surface of the light emission surface 16. A plurality of LEDs 3 are arranged opposite to the light entrance surface 11, and the light enters the light guide plate 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a backlight used for a liquid crystal display of a car navigation system, a liquid crystal television, a mobile phone and the like.

  As a conventional backlight unit, at least one point light source for projecting light is disposed on the edge of a light guide plate having a hologram pattern formed on the back surface. In the vicinity of the point light source, there is an invention including a light transmission region that transmits light as it is, a blazed portion in which a sawtooth blazed pattern is formed, and a prism portion in which a triangular prism pattern is formed. (For example, refer to Patent Document 1).

JP 2004-213025 A (pages 4-7, FIGS. 10, 16)

  In an edge-light type backlight unit in which a light source is arranged on the side surface of a light guide plate, it is known that unevenness in luminance is less likely to occur on the light exit surface when light incident on the light guide plate is repeatedly reflected in the light guide plate. Yes.

  However, as in Patent Document 1, an edge light type backlight unit using a light emitting diode (hereinafter referred to as LED) has a problem of uneven luminance on the light emitting surface because the LED is a point light source. That is, due to the high light emission luminance and directivity of the LED, the light exit surface can be bright and dark, and uneven brightness tends to occur depending on the location. Here, the brightness unevenness on the light exit surface includes the brightness unevenness that occurs from the light entrance surface of the light guide plate toward the back and the brightness unevenness that occurs in the direction of the light entrance surface. Of Patent Document 1

Describes that there is a possibility that an intermediate region between the LEDs may be a dark region.

  With respect to this problem, in the backlight unit of Patent Document 1, a refractive member including a light transmission region, a blazed portion, and a prism portion is disposed between the light incident surface of the light guide plate and the point light source, thereby providing light output. It is described that the brightness of the surface can be made uniform.

  However, after the light from the point light source is incident on the refracting member, it is emitted from the transmission region, the blaze portion or the prism portion, passes through a medium such as air, and enters the light guide plate incident surface. There are problems that light is lost when light enters and exits, and that the effective light emitting surface of the backlight unit is reduced because the refractive member itself cannot be used as the light emitting surface.

  An object of the present invention is to provide a backlight that improves the uniformity of luminance of the light emitting surface, reduces light loss, and has a large effective light emitting surface.

In order to achieve the above object, a backlight according to the present invention is located on an end surface, and is a light incident surface on which light is incident, a reflective surface that reflects incident light, and a ridge line that intersects the light incident surface at a substantially right angle. A plurality of light-transmitting light guide plates having a light exit surface for emitting incident light from the prism portion, and a plurality of light guide plates arranged along the longitudinal direction of the light incident surface. And a point light source for allowing light to enter the light plate.

  According to the present invention, it is possible to realize a backlight having a high luminance uniformity on the light emitting surface, a small light loss, and a large effective light emitting surface.

(First embodiment)
Hereinafter, a backlight according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view for explaining a first embodiment of a backlight according to the present invention, and FIG. 2 is a perspective view for explaining a light guide plate and a light source.

  The light guide plate 1 is made of, for example, acrylic having translucency, and includes a light incident surface 11, reflecting surfaces 12 to 15, and a light emitting surface 16. The light incident surface 11 is a surface on which light is mainly incident on the light guide plate 1, and is located on the end surface of the light guide plate 1.

  The reflecting surfaces 12 to 15 are surfaces that mainly reflect the light incident on the light guide plate 1. The plane orthogonal to the light incident surface 11 is the reflecting surface 12, and the plane facing the light incident surface 11 is the reflecting surface 13. Are the reflecting surfaces 14 and 15, respectively. Although not shown in the drawing, the reflecting surface 12 is subjected to light diffusion processing such as dot printing, blast processing, and groove processing as means for emitting light from the light output surface 16. When light is incident on the portion where these are applied, the light reflection direction changes, so that the light can be emitted from the light exit surface 16. In this light diffusion process, the number of light diffusion processes is increased or increased from the light incident surface 11 side toward the reflective surface 13, so that the light exit surface 16 has a direction from the light incident surface 11 toward the back. The amount of emitted light can be adjusted, and the light emission of the backlight is uniform, that is, the light emission with high uniformity can be obtained.

  The light exit surface 16 is a surface that mainly emits light incident on the light guide plate 1, and a plurality of triangular prisms 161 having an apex angle of 90 degrees are continuously formed on the surface, and the ridge is further formed. The ridge line corresponding to the portion intersects the light incident surface 11 at a substantially right angle. Here, “intersect substantially at right angles” means that even if the light incident surface 11 and the ridgeline of the prism portion 161 have an inclination of 90 degrees or several degrees with respect to 90 degrees, it is allowed. This is because the effects of the present invention can be obtained even if there is some error with respect to 90 degrees.

  On the opposite side of the light incident surface 11 of the light guide plate 1, an elongated substrate 2 having a wiring pattern formed on the surface is arranged in parallel. The wiring pattern on the substrate 2 is, for example, a surface-mounted white light emitting diode. Several LED3 is arrange | positioned at equal intervals in the longitudinal direction. The distance between the substrate 2 and the plurality of LEDs 3 and the light incident surface 11 of the light guide plate 1 is short enough to allow light from the LEDs 3 to efficiently enter the light incident surface plate 11 and is always maintained at a constant distance.

  Here, various optical sheets are disposed on the reflecting surfaces 12 to 15 and the light exiting surface 16 of the light guide plate 1 in order to increase the luminance as a backlight. On the reflection surfaces 12 to 15, a reflection sheet 4 having high reflectivity is provided for allowing light that has been emitted from the light guide plate 1 to be incident again and reducing light loss.

  The light exit surface 16 is provided with a diffusion sheet 5 for diffusing light into uniform surface light emission, and a prism sheet 6 for concentrating the light in the forward direction to increase the brightness is further provided on the light exit surface 16. The ridge lines are arranged so as to be orthogonal to the ridge lines of the prism portions 161 of the light incident surface 11.

  Each component described above is surrounded by a housing 7 having a light extraction surface formed on the light output surface 16 side as shown in FIG.

  3A and 3B are diagrams for explaining the luminance of the light emitting surface of the conventional and the backlights of the present invention. FIG. 3A is a conventional backlight having a planar light emission surface, and FIG. It is the backlight of the present invention in which a plurality of prisms are formed on the light exit surface.

  The specifications at the time of experiment of the backlight of FIG. 3 (a) and (b) are demonstrated. In (a), the light guide plate has a flat rectangular shape with a light exit surface size of 8 inches and a thickness of 3.6 mm, and the LED has a directivity angle of 120 degrees and uses 15 white light emitting diodes. Furthermore, in (b), the prism on the light exit surface is an isosceles triangle, the apex angle is 90 degrees, and the distance between adjacent ridge lines is 100 μm.

  In FIG. 3A, a clear bright and dark portion is generated on the light exit surface near the light entrance surface. This can be said that the light emitted from the LED 3 does not spread so much and is emitted in the forward direction of the LED 3. On the other hand, in FIG. 3 (b), although it is slightly bright and dark in the vicinity of the light incident surface, it cannot be discovered without care.

  Next, the operation of the present invention will be described. 4A and 4B are diagrams for explaining the operation of the conventional and the light guide plate of the backlight according to the present invention. FIG. 4A is a conventional backlight having a planar light emission surface, and FIG. It is the backlight of the present invention in which a plurality of prism portions are formed on the light exit surface. Here, in FIG. 4, for convenience of explanation, the LED 3 is disposed immediately below the prism portion 161, light is incident from the (reflection) surface 12 side of the light guide plate 1, and incident on the light guide plate 1 from the LED 3 side. In this case, it is assumed that light is incident without being refracted. In addition, an alternate long and short dash line X-X ′ in the drawing is a line perpendicular to the surface 12 and passing through the LED 3.

  In FIG. 4A, incident light 811 that is incident on the light guide plate 1, reaches the light exit surface 16, and is perpendicular to the light exit surface 16 is not affected by refraction unlike the output light 812, and is incident light. The light is emitted on the extension line 811. Further, the incident light 821 having an incident angle smaller than the critical angle with respect to the light incident surface 16 is refracted from the light emitting surface 16 and emitted to the outside of the light guide plate 1 like the emitted light 822, and incident larger than the critical angle. The light 831 is totally reflected like the reflected light 832 and returned to the light guide plate 1.

  That is, when the light from the LED 3 is viewed from the observation point Y on the alternate long and short dash line XX ′ through the light guide plate 1, only the outgoing light 812 incident substantially perpendicular to the light exit surface 16 can be seen. it can.

  In FIG. 4B, the incident light 841 incident substantially perpendicular to the light exit surface 16 has an incident angle larger than the critical angle due to the inclination of the prism portion 161 of the light exit surface 16. The light is not totally emitted from the light guide plate 16 but totally reflected in the light guide plate 1 like the reflected light 842. The outgoing light 851 emitted from the LED 3 in a wide range is emitted from the outgoing surface 16 like the outgoing light 852 because the angle with the surface of the prism portion 161 is smaller than the critical angle. Further, since the incident light 862 is also incident at an angle smaller than the critical angle, the incident light 862 is emitted from the emission surface 16, but is emitted like the emitted light 862 depending on the incident direction.

  That is, when the light from the LED 3 is viewed from the observation point Z on the alternate long and short dash line XX ′ via the light guide plate 1 having the prism portion 161, the incident light 841 incident perpendicularly to the light exit surface 16 is obtained. Since it cannot be seen, the light source cannot be seen at the position of the LED 3 actually arranged. Visible from the observation point Z are the outgoing light 862 of the incident light 861 and the outgoing light 872 of the incident light 871 that is symmetric with respect to the straight line between the LED 3 and the observation point Z. Therefore, since it seems to be emitted from the position of the pseudo LED 3 ′ arranged on the extension line of the emitted light 862 and 872 and at a position separated by the optical path length from the LED 3 to the light emitting surface 16, the light spreads. appear.

  As a result, in the edge-light type backlight, when a point light source and a light guide plate having a flat light output surface are combined, a bright portion is formed in the front direction of the LED 3 on the light output surface 16 near the light input surface 11 of the light guide plate 1. A dark part appears between adjacent LEDs 3, resulting in uneven brightness. As in the present invention, a light guide plate having a light exit surface on which a prism in which a point light source and a ridge line intersect at right angles with the light incident surface is formed. In combination, it is possible to obtain an effect of uniforming the luminance of the light exit surface 16.

  In this embodiment, the LED 3 that is a point light source is usually used as a light source by forming a plurality of prism portions 161 having ridge lines intersecting at right angles to the light incident surface 11 on the surface of the light guide plate 1. Therefore, unevenness in luminance generated on the light exit surface 16 near the light entrance surface 11 can be prevented.

  Moreover, since only the shape of the light exit surface 16 is deformed to prevent luminance unevenness in the vicinity of the light entrance surface 11, the entire light exit surface 16 can be used as the light emitting surface of the backlight. Can be greatly increased. At the same time, light loss can be reduced, so that an efficient backlight can be realized.

  Furthermore, since the prism portion 161 also has an effect of increasing the luminance in the forward direction in addition to the above-described effect, the number of prism sheets can be reduced.

(Second Embodiment)
FIG. 5 is a perspective view for explaining a backlight according to the second embodiment of the present invention. About each part of this 2nd Embodiment, the same part as each part of the backlight of 1st Embodiment is shown with the same code | symbol, and the description is abbreviate | omitted.

  In the second embodiment, the light guide plate 1 has a flat rectangular shape and includes a light incident surface 11, reflection surfaces 12 to 15, and a light output surface 16, and a plurality of prism portions are provided on the light output surface 16. The prism sheet 9 having 91 is disposed so that the ridge line thereof is perpendicular to the light incident surface 11. Here, in the present embodiment, the prism sheet 9 in which the apex angle of the prism portion 91 is 90 degrees and the distance between adjacent ridge lines is 50 μm is used.

  In the present embodiment, the prism sheet 9 is disposed on the light exit surface 16 so that the ridge line of the prism portion 91 is perpendicular to the light incident surface 11, so that the backlight is the same as the backlight of the first embodiment. The luminance unevenness of the light exit surface 16 in the vicinity of the light incident surface 11 can be prevented, and the effect of improving the front brightness that is normally obtained when a prism sheet is provided can also be obtained.

  Moreover, the effective light emission surface can be made large similarly to the backlight of 1st Embodiment. Further, since there is little light loss, an efficient backlight can be realized.

  Furthermore, in the second embodiment, since the prism sheet 9 can be formed only in a predetermined direction on the flat rectangular light guide plate 1 having a flat light output surface 16, the manufacture is easy.

  Here, the effect of the second embodiment is an effect that can be obtained by first disposing the prism sheet 9 on the light output surface 16 of the light guide plate 1. That is, even if another optical sheet is disposed and the ridge line of the prism sheet is disposed perpendicular to the light incident surface 11, the same effect as that of the present invention cannot be obtained.

  In addition, embodiment is not necessarily restricted above, For example, you may change as follows.

  The light guide plate 1 may have a wedge shape in which the thickness of the light guide plate decreases from the light incident surface 11 toward the reflective surface 13. Further, a surface facing the light incident surface 11 of the light guide plate 1 may be a light incident surface, and a backlight system in which light from the LED 3 is incident in both directions may be employed. In that case, the unevenness of the light exit surface is further reduced by arranging the plurality of LEDs opposed to one light incident surface and the plurality of LEDs opposed to the other light incident surface in a staggered manner. .

  The prism portion 161 (or 91) may be formed only on the light exit surface 16 in the vicinity of the light entrance surface 11, and in this case, the luminance unevenness in the vicinity of the light entrance surface 11 can be reduced.

  In addition, the prism portion 161 (or 91) may be formed so that one or both of the peak and valley portions of the prism are semicircular as shown in FIGS. 6 (a) and 6 (b). In this case, the light in the forward direction of the LED 3 can be enhanced compared to the case where the prism portion 161 is triangular. Therefore, the luminance distribution on the light exit surface 16 can be adjusted. Also, as shown in FIGS. 6C and 6D, even if the shape of the peak, valley, or both of the prism is trapezoidal, the same effect as in the case of FIG. Obtainable.

  Furthermore, the prism angle of the apex angle of the prism portion 161 or 71 may be changed within a range of 60 degrees to 120 degrees, for example.

  In the second embodiment, the apex angle of the prism portion 91 of the prism sheet 9 may be arranged toward the light exit surface 16 side.

Sectional drawing for demonstrating 1st Embodiment of the backlight of this invention. The perspective view for demonstrating a light-guide plate and a light source. The figure for demonstrating the brightness | luminance of the light emission surface of the backlight of the past and this invention The figure for demonstrating the effect | action of the light-guide plate of the backlight of this invention conventionally. The perspective view for demonstrating the backlight of the 2nd Embodiment of this invention. The figure for demonstrating the other shape of a prism part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light guide plate 11 Light-incidence surface 12-15 Reflective surface 16 Light-emitting surface 161, 91 Prism part 2 Board | substrate 3 LED
4 Reflective sheet 5 Diffusion sheet 6, 9 Prism sheet 7 Case

Claims (2)

A plurality of prism portions having a light incident surface that is incident on the end surface, a light incident surface that reflects light, a reflective surface that reflects incident light, and a ridge line that intersects the light incident surface substantially at right angles are formed. A light transmissive light guide plate having a light exit surface to be emitted from the prism portion;
A backlight comprising: a plurality of point light sources arranged along the longitudinal direction of the light incident surface and allowing light to enter the light guide plate. A translucent light guide plate that is located on the end face and has a light incident surface on which light is incident, a reflective surface that reflects incident light, and a light output surface that emits incident light;
A prism sheet disposed on the light exit surface so as to have a plurality of prism portions, and a ridge line of the prism portion is substantially perpendicular to the light incident surface;
A backlight comprising: a plurality of point light sources arranged along the longitudinal direction of the light incident surface and allowing light to enter the light guide plate.

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