WO2009098797A1

WO2009098797A1 - Surface light, source and illuminated signboard

Info

Publication number: WO2009098797A1
Application number: PCT/JP2008/065619
Authority: WO
Inventors: Yoshihiro Sakai
Original assignee: Light Engine Limited
Priority date: 2008-02-05
Filing date: 2008-08-25
Publication date: 2009-08-13
Also published as: JP2011034674A

Abstract

A tray-shaped box body has, for example, a square bottom surface, an open upper surface, a light-reflecting member provided on an inner surface thereof, side walls inclined outward, and holes formed at least at two positions of the side walls near the bottom surface of the box body. LEDs are provided outside the holes, so as to emit light to an inner space of the box body. Protruding portions are formed at upper sides of the holes formed at the side walls of the box body, so as to extend from the side walls.

Description

DESCRIPTION

EXPOSURE METHOD, EXPOSURE APPARATUS AND DEVICE MANUFACTURING

METHOD

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a PCT International Application claiming priority to Japanese Patent Application No. 2008-025339, filed February 5, 2008, the entirety of which is incorporated herein by reference.

[0002] Throughout this application, several publications are referenced. Disclosure of these references in their entirety is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0003] The present invention relates to surface light sources applied to, for example, backlights of liquid crystal display devices or lightings of illuminated signboards, and relates to illuminated signboards using the surface light sources. More particularly, the present invention relates to a surface light source employing a semiconductor light-emitting device such as a light-emitting diode, the surface light source being applicable to a backlight of a liquid crystal display device such as a large-thin-screen television, realizing saving of electric power, being bright, and being capable of equalizing surface brightness and chromaticity, and relates to an illuminated signboard using the surface light source.

2. Description of the Related Art

[0004] To conform with the recent trend of electric power saving, for example, in large-screen liquid crystal display devices and illuminated signboards, semiconductor light- emitting devices (hereinafter, also referred to as LEDs) driven with low voltages have begun to be used as backlights instead of cold-cathode tubes. Fig. 12 illustrates an example configuration in which light of LEDs 112 is introduced from side surfaces of a light-guiding plate 111, a light-reflecting surface is provided on a back surface thereof, and the light is emitted from a front surface thereof (for example, see Japanese Unexamined Patent Application Publication No. 7-320514) . Figs. 13A and 13B illustrate another example configuration in which light- emitting devices 112 (chips or LED products) are arrayed on a reflection plate 113, thereby equalizing an in-plane light intensity (brightness) at a position of a light-diffusing member 114 through spontaneous diffusion of the light, and light with a uniform brightness is emitted from a front surface of the light-diffusing member 114, so that the configurations functions as a backlight.

[0005] In the former configuration, it is possible to substantially equalize the in-plane brightness by using the light-guiding plate in a small liquid crystal panel having a side of about 50 mm or smaller. However, it is difficult to completely equalize the in-plane brightness in a liquid crystal display device larger than the above-mentioned liquid crystal panel. Hence, a plurality of light-guiding plates has to be arrayed to provide a large light source. Since light is introduced from the side surfaces of the light-guiding plate 111, the light sources (LEDs 112) may be obstructive. It is difficult to provide a large light source with a uniform brightness by arraying the light- guiding plates (that is, the in-plane brightness may be uneven at portions corresponding to the LEDs 112) . Namely, it is difficult to provide a surface light source of a desired size by arraying (tiling) a plurality of light- guiding plates.

[0006] In the latter configuration, the arrayed LEDs may be merely aligned by a desired number to obtain a desired size, thereby providing a surface light source with the desired size. The configuration may be practically applied to, for example, a backlight of a currently available large- screen liquid crystal television. In the configuration, however, light from the individual LEDs 112 is directly emitted onto a liquid crystal panel through the light- diffusing member 114. Hence, to obtain a uniform brightness in an area between adjacent LEDs 112, a distance d from a bottom surface of an LED 112 to the light-diffusing member 114 should be at least about 70 mm; otherwise, the brightness may be decreased in the area between the adjacent LEDs 112. (Although the light-diffusing member 114 is provided, the light-diffusing member 114 merely eliminates the directivity of light, but does not have a function of mixing light, unlike the light-guiding plate.) In addition, LEDs, even white LEDs, exhibit variations in chromaticity . When white light is made by mixing light of LEDs of R, G, and B, the colors may not be completely mixed unless the distance to the light-diffusing member 114 is further increased, resulting in an uneven chromaticity. The increase in distance d, however, may increase the thickness of the screen, and may decrease the brightness of light emitted from the front surface of the light-diffusing member 114 by a value inversely proportional to d squared. [0007] To address these disadvantages, a surface light source unit 1 has been suggested by the inventor of the present invention (for example, see Japanese Unexamined Patent Application Publication No. 2007-207752), as shown in a plan view in Fig. HA and in a cross-sectional view in Fig. HB illustrating a direction in which light propagates. In the surface light source unit 1, LEDs 7 are arranged at least at two corner portions of a bottom surface of a tray- shaped box body 11 in a rota^'tionally symmetric manner. A light-reflecting member is provided on an inner surface of the box body 11 to increase an irregular reflection characteristic. Side walls lie of the box body 11 are inclined. Light of the LEDs 7 is mixed to equalize the brightness and chromaticity of the light in the box body 11. The inclination angle of the side walls lie of the box body 11 is adjusted, so that the in-plane brightness on the front surface of the box body 11 is equalized.

[0008] In order to equalize the brightness in the plane of opening of the tray-shaped box body 11, the light source in which the LEDs 7 are arranged at the bottom surface of the box body 11, the light from the LEDs 7 is reflected by the bottom surface and the side surfaces of the box body 11, and the brightness of the light is equalized while the light is reflected and mixed in the box body 11. It is necessary that a major portion of the light from the LEDs 7 is emitted onto the side walls lie, the side walls lie having a height of about 14 mm. Hence, the LEDs 7 with a directivity ranging from 45° to 60° (22° to 30° with respect to the center axis) are arranged at the bottom surface of the box body 11 so as to emit the light toward the bottom surface and in a horizontal direction. As a result, the light emitted from the LEDs 7 and diverging downward is reflected by the bottom surface of the box body 11, and the light does not diverge upward at a wide angle. Thus, a major portion of the light diverging upward is reflected by the side walls, is mixed in the box body 11 while being reflected, and is emitted from the plane of opening, thereby equalizing the brightness. To obtain such LEDs with a directivity ranging from 45° to 60°, however, the LED should be a dome LED, or a condensing lens portion should be provided on the surface of an LED when the LED is a chip LED. The dome of the dome LED or the lens portion of the LED is formed of epoxy resin or the like. Epoxy resin is likely to be deteriorated by light, and if the epoxy resin is deteriorated and discolored, the brightness is decreased, and a cost is incurred. [0009] In contrast, when an LED with a large angle of divergence (which represents an angle of divergence of light emitted from an LED, the same will apply hereinafter) is used, light with a large angle of divergence mainly propagates directly upward. Hence, referring to portions with a high brightness (portions indicated by oblique lines) of a light-diffusing member 13 provided on the surface light source unit 1 in Fig. HC, it is difficult to equalize the in-plane brightness. This is because, in the known configuration, the light propagating upward with the angle of divergence of 60° (30° with respect to the bottom surface of the box body 11) is not incident on the side walls Hc, but is directly emitted to the outside as shown in Fig. HD for an illustration showing a direction in which light propagates like Fig. HB. However, the light enters the light-diffusing member 13 together with light with a high intensity (because the light path from the LED 7 as the light source is short) with the angle of divergence of 120° (60° with respect to the bottom surface of the box body 11) of the LED 7, the brightness is increased. As a result, when the angle of divergence of the LED 7 is large, it is difficult to equalize the in-plane brightness of the surface light source unit 1. Also, the mixing is insufficient. Thus, it is also difficult to obtain a uniform chromaticity .

SUMMARY OF THE INVENTION

[0010] In light of the above situations, an object of the present invention is to provide a surface light source with a uniform brightness, the surface light source having surface light source units arrayed by a desired number, and being applicable to a thin-large-screen liquid crystal television and to an illuminated signboard. The surface light source units use semiconductor light-emitting devices (LED) , which have no lens portion, which are inexpensive, and which hardly cause a brightness to be decreased as a result of discoloring. The LEDs are arranged at a bottom surface of a tray-shaped box body, thereby providing a uniform in-plane brightness. [0011] Another object of the present invention is to provide a thin, illuminated signboard driven with low electric power and being capable of uniform display even when the illuminated signboard is applied to one having a large display panel.

[0012] A surface light source unit according to an aspect of the present invention includes a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light- reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward; and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body. Also, protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls.

[0013] Herein, the semiconductor light-emitting device may be a typical semiconductor light-emitting device (LED) having any of various structures. The semiconductor light- emitting device may be a dome LED, a chip LED, or an LED with a lens. In particular, an advantage of the aspect of the present invention is efficiently attained when an LED does not have a lens, and has a large angle of divergence. The LED is not limited to an LED emitting white light, and may include LEDs emitting light of red (R) , green (G) , and blue (B) , and the light of the colors of R, G, and B may be mixed.

[0014] Each of the protruding portions may have a length at a center portion thereof so that the protruding portion shields light emitted from an upper edge of a light-emitting surface of the corresponding light-emitting device at an angle of 40° or larger with respect to a horizontal plane, and so that the protruding portion does not shield light emitted at an angle of 20° or smaller. Light directly emitted upward is reflected by the protruding portion, is directed to the bottom surface of the box body, and then, is reflected by the bottom surface. Accordingly, this configuration is preferable because the reflection of the light is repeated in the box body, and the brightness of the light is equalized.

[0015] The protruding portions may be formed such that cut portions for forming the holes at the side walls of the box body are partly bent. Accordingly, the protruding portion can be easily formed without any additional material. [0016] The box body may have a rectangular shape in plan view. Also, the light-emitting devices may be provided at four corners of the box body, or at center portions of four side walls of the box body. Alternatively, two or more LEDs may be provided at each corner portion. [0017] A surface light source according to another aspect of the present invention includes a surface light source unit; and a case made of a light transmissive material. The surface light source unit includes a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light- reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward; and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body. In the surface light source unit, protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls. In the surface light source, at least a plane- of-opening side of the box body is covered with the case. Also, power connection means is led to the outside from the case. Alternatively, a surface light source according to still another aspect of the present invention includes a plurality of arrayed surface light source units; and a light-diffusing member provided to cover the plurality of surface light source units.

[0018] When the plurality of surface light source units are arrayed without a gap, the brightness of light is more likely to be equalized in the entire plane of opening, and the distance between the box body and the light-diffusing member can be decreased, thereby providing a thin surface light source. However, if the surface light source does not have to be thin or bright, the surface light source units may be arrayed with a gap. The light-diffusing member may be a typical light-diffusing plate formed of a translucent plate member of so-called translucent acryl, such as opaque white acrylic resin (PMMA), polyethylene terephthalate (PET), polycarbonate, or glass. Alternatively or additionally, a condensing prism, a display panel, or a liquid crystal panel may be directly arranged.

[0019] An illuminated signboard according to yet another aspect of the present invention includes a surface light source; and a light-diffusing member and a display panel provided on a front surface side of a surface light source at a predetermined distance from a front surface of the surface light source. The surface light source includes a plurality of arrayed surface light source units. Each of the surface light source units has a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light- reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward; and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body. In each surface light source unit, protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls.

[0020] With any of the aspects of the present invention, the protruding portion is formed at the side wall of the tray-shaped box body at the position where the light from the LED provided near the bottom surface of the box body is incident. Accordingly, the light is not directly emitted from the upper plane of opening of the box body even when the LED has a large angle of divergence. Light directed upward is reflected downward by the protruding portion. Thus, unevenness of the brightness, such as being noticeably bright in an area above the LED, does not appear. Also, the light reflected by the protruding portion is repeatedly reflected in the box. Accordingly, the light is irregularly reflected by the bottom surface and the side walls of the box body, and is mutually mixed with each other in the box body. Thus, the brightnesses, chromaticities, and luminescent colors of the light-emitting devices provided at least at the two positions are equalized, and the light is emitted from the upper plane of opening of the box body with a uniform brightness. As a result, an LED with a narrow directivity with an angle of divergence ranging from 45° to 60° does not have to be used, and an LED with a wide directivity may be used. Also, an LED with no lens portion may be used. Accordingly, resin for forming a lens is not necessary, deterioration of the resin over time can be avoided, and the LED can be manufactured inexpensively. [0021] In addition, when the LED with the wide directivity is used, LEDs do not have to be respectively arranged at corner portions in a rotationally symmetric manner so that an irradiation region of a single LED is mainly allocated to a half of the entire area of the box body unlike the known configuration. For example, an LED with an angle of divergence of about 120° is used, the LED may be arranged to emit light to the entire inner space of the box body from a corner portion of the bottom surface, or may be arranged at a center portion of a side near the bottom surface. With either arrangement, a single LED can irradiate the substantially entire inner space of the box body with light, while the protruding portion prevents upward directed light from being directly emitted to the outside of the box body. Although the irradiation of the light may be reduced in an area near the LED because the LED shades the light, the shaded area can be irradiated with light with high intensity by providing another LED at a center portion of an opposite side. Hence, the brightness can be substantially equalized in the entire area. That is, since the two LEDs are oppositely provided, the shaded portions may be compensated as the LEDs mutually emit light to the shaded portions, and the light from the LEDs may be mixed in residual portions. Accordingly, even when the LEDs exhibit variations in brightness and chromaticity, the brightness and chromaticity can be equalized. Also, by increasing the number of LEDs, the brightness and chromaticity can be further efficiently equalized.

[0022] While two LEDs may be arranged at least at opposite two corner portions of the tray-shaped box body, if the angle of divergence is large, an LED is preferably arranged such that a light-emitting surface thereof is directed to emit the entire area of the box body. Since the LED is provided outside the bottom surface of the tray-shaped box body so as to emit light to the inner space of the box body from the hole formed at the side wall of the box body, a gap is formed near the bottom surface when a plurality of box bodies are arrayed to define a large surface light source. LEDs and connection portions of leads may be provided in the gap without a portion protruding outward at the front surface of the box body. By arraying the box bodies in a matrix form by a desired number, a surface light source with a desired size without a gap can be obtained. As a result, a large illuminated signboard driven with low electric power, with a long life, and without necessity of maintenance can be provided by using LEDs. Depending on the purpose of use, an illuminated signboard may be defined by arraying the box bodies with a predetermined gap.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figs. IA to 1C are a plan view, a side view, and a cross-sectional view each showing a surface light source unit according to an embodiment of the present invention; [0024] Figs. 2A and 2B are a schematic illustration showing a length of a protruding portion in Figs. IA and IB, and an expansion plan showing a box body in Figs. IA to 1C; [0025] Figs. 3A to 3F are illustrations showing examples of a chip light-emitting device according to the embodiment of the present invention;

[0026] Figs. 4A and 4B are illustrations each showing another example of a surface light source unit according to the embodiment of the present invention;

[0027] Figs. 5A and 5B are explanatory illustrations, Fig. 5A schematically showing irradiation regions of LEDs when the present invention is applied to the surface light source unit in Figs. IA to 1C to make a large surface light source, Fig. 5B schematically showing a state in which light of the LEDs is irregularly reflected in a box body;

[0028] Figs. 6A and 6B are a plan view and a cross- sectional view each showing an illuminated signboard using the surface light source units in Figs. IA to 1C according to an embodiment of the present invention;

[0029] Fig. 7 is a fragmentary enlarged view of Fig. 6B;

[0030] Figs. 8A and 8B are illustrations showing a relationship between a pitch (gap) and a distance to a light-diffusing member provided at an upper side when the surface light source units are arrayed with a gap;

[0031] Fig. 9 is an illustration showing an arrangement example of a surface light source when the surface light source is applied to an illuminated signboard which does not illuminate the entire area of the signboard, but illuminates only a region of a character or the like;

[0032] Fig. 1OA and 1OB are illustrations each showing an example in which a surface light source includes a single surface light source unit;

[0033] Figs. HA to HD are illustrations each showing a problem in angles of divergence of LEDs in a surface light source unit using a known tray-shaped box body;

[0034] Fig. 12 is an illustration showing an example of a backlight using a known light-guiding plate; and

[0035] Figs. 13A and 13B are illustrations each showing an example of a known direct-type backlight in which LEDs are arrayed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] A surface light source and an illuminated signboard according to embodiments of the present invention are described below with reference to the attached drawings. Fig. IA is a plan view, Fig. IB is a cross-sectional view taken along line B-B in Fig. IA, and Fig. 1C is a cross- sectional view of a box body according to an embodiment of the present invention. Referring to Figs. IA to 1C, a surface light source unit according to the embodiment of the present invention includes a tray-shaped box body 11. The box body 11 is open at an upper surface thereof, and has a bottom surface of a polygon with three or more corners (for example, square as shown in Fig. IA) . The box body 11 includes a light-reflecting member lib on an inner surface thereof, side walls lie inclined outward, and holes Hd formed at least at two of the side walls Hc near the bottom surface. Semiconductor light-emitting devices (LEDs) 7 are respectively provided outside the holes Hd so as to emit light to an inner space of the box body 11. In this embodiment, protruding portions Hh are formed at upper sides of the holes Hd formed at the side walls Hc of the box body 11, so as to extend from the side walls Hc. [0037] Referring to the cross-sectional view in Fig. 1C, for example, the box body 11 is formed such that the light- reflecting member Hb made of E60, which is a product name of polyester expanded sheet with a thickness of about 180 μm, produced by Toray Industries, Inc., is bonded onto a surface of an aluminum plate 11a with a thickness of about 0.35 mm, the aluminum plate 11a is punched as shown in Fig. 2B

(described later), and edges are bent to obtain a tray shape. In this embodiment, the aluminum plate 11a is punched not only to obtain a tray-shaped box body, but also to form the holes Hd to introduce light to an inner space of the box body 11 from the LEDs 7 provided outside the bottom surface of the box body 11 as well as to leave the protruding portions Hh formed at the upper sides of the holes Hd.

[0038] Referring to Fig. IB, which is the cross-sectional view taken along line B-B in Fig. IA (the light-reflecting member Hb being omitted) , the holes Hd are formed in bottom portions of the side walls Hc of the box body 11 so that the light emitted from the LEDs 7 is emitted to the inner space of the box body 11. In the embodiment in Figs. IA to 1C, the LEDs 7 are arranged at the corner portions of the box body 11 to emit light to the entire area in the box body 11. Hence, referring to an expansion plan in Fig. 2B, the holes Hd are formed such that each hole Hd across the two adjacent side walls Hc. Also, in this embodiment, the protruding portions Hh are formed at the upper sides of the holes Hd. The protruding portions Hh are formed such that portions of a plate member to be punched and eliminated are partly left as shown in Fig. 2B, and the left portions are bent . [0039] Referring to Fig. 2A, which is a fragmentary enlarged view of Fig. IB, a length S of a center portion (with a maximum length) of the protruding portion Hh is determined such that light emitted from a top portion of a light-emitting surface (light radiation surface) of an LED 7 (71) is shielded (reflected) when being emitted at an angle of 40° or larger with respect to the bottom surface, and is directly emitted when being emitted at an angle of at least 20° or smaller. (Through described later, a light-emitting region of an LED 71 is located at a slightly inner side of an outer peripheral portion of the LED 71.) Since the LED 7 is provided so as to maximally introduce the emitted light into the box body 11, the light-emitting surface of the LED 7 is provided substantially at a position facing the hole Hd. The lower limit of the length S at the center portion is determined such that light emitted from the top portion of the light-emitting surface of the LED 7 with an angle of divergence of 80°, that is, light emitted from the top portion of the light-emitting surface of the LED 7 at an angle of 40° or larger with respect to the bottom surface of the box body 11 is reflected and restored to the inner space of the box body 11 so as not to be emitted to the outside of the box body 11. Also, the upper limit of the length S at the center portion of the protruding portion Hh is determined such that light with an angle of divergence of 40°, that is light emitted from the top portion of the light-emitting surface at an angle of 20° or smaller with respect to the bottom surface of the box body 11 is not shielded, and is directly emitted.

[0040] As a result, an advantage similar to that obtained when an LED 7 having an irradiation characteristic with an angle of divergence ranging from 40° to 80° can be attained. Light with a large angle of divergence is reflected by the protruding portion Hh toward the bottom surface of the box body 11, and then is reflected by the bottom surface. The light is emitted to the outside of the box body 11 while the light is reflected by the side wall Hc of the box body 11, is directly emitted to the outside, and is mixed. Thus, when an LED 7 even with a large angle of divergence is used, a portion with a noticeably large brightness is not produced in the area above the LED 7, and hence, an uneven brightness does not appear. The protruding portion Hh shields the light emitted at the angle of 40° or larger with respect to a horizontal plane (bottom surface of the box body 11) . Hence, the protruding portion Hh may be directed upward at an angle of about 30° with respect to the horizontal plane without any problem. With the angle, the light reflected by the protruding portion Hh easily diverges toward the entire inner space of the box body H. [0041] Referring to Fig. IA, the protruding portion Hh has a shape whose length is long at the center portion and is decreased toward the periphery, because the brightness of the light-emitting surface is uneven. The light-emitting surface has a high brightness at a center portion provided with an LED chip, whereas the light-emitting surface has a low brightness at a peripheral portion and emits a small quantity of light to the outside.

[0042] The side wall lie, which is bent as described above, has a height and a bending angle determined so that light is efficiently reflected in the box body 11, and so that the light is effectively emitted from the plane of opening. For example, when a side A of the outer periphery is 80 mm (square, the same will apply hereinafter) , a side B of the bottom surface is about 54.4 mm, and a height C is about 14.2 mm. When the side A of the outer periphery is 100 mm, the side B of the bottom surface is about 74.4 mm, and the height C is about 19.2 mm. The light-reflecting member lib is an expanded sheet, and hence, has irregularities on a surface thereof, thereby serving as an irregularly reflecting surface for reflection in various directions. In particular, the height C of the box body 11 ranges from about 10 to 20 mm depending on the size of the bottom surface of the box body 11, and the brightness can be almost (substantially) equalized in the upper surface. [0043] Alternatively, the light-reflecting member lib may be made of, for example, MCPET, which is a product name of an extra-fine expanded light-reflecting plate, produced by Furukawa Electric Co., Ltd., with a thickness of about 1 to 2 mm.

[0044] The side walls lie of the box body 11 may have a uniform height when a single surface light source unit is used. Though described later, when a plurality of surface light source units 1 are arrayed to define a large surface light source, a height of two of the side walls may be larger than a height of the residual walls so as to prevent the thickness of the side walls to be doubled at a joint. In Fig. IA, the height of the upper and right side walls lie is larger than the height of the residual side walls lie. Hence, steps are formed at portions D.

[0045] The surface of the light-reflecting member lib of the box body 11 is coated with titanium oxide powder or the like. Hence, when ultraviolet rays are generated from LEDs, the powder functions as a photocatalyst to dissolve organic substances adhering to the surface of the light-reflecting member lib, thereby making dirt less noticeable, and preventing contamination with dust or the like while the reflectivity is substantially prevented from deteriorating. As a result, a semiconductor light-emitting device with a markedly long life can be used as a light source, and can be used for a long period without maintenance while the brightness is not decreased.

[0046] To fabricate such a box body 11, for example, the above-described aluminum plate is bonded onto the light- reflecting member, thereby forming the plate body; the plate body is punched to have the through holes Hd for introducing the light of the LEDs 71, the protruding portions Hh, and the side walls Hc; the side walls Hc are bent and secured; and the protruding portions Hh are raised to be parallel to the bottom surface or to be directed slightly upward, thereby fabricating the desired protruding portions Hh and the side walls Hc having a desired inclination. Herein, reference numeral He denotes a rivet hole for fixing the box body H to a housing (not shown) by using a rivet or the like.

[0047] In the embodiment illustrated in Figs. IA to 1C, the LED 7 is a side-view LED 71 as shown in Fig. 3A. The LED 7 may be any type. With such a side-view LED 71, a pair of leads 711 and 712 are provided on side surfaces of the LED 71. Merely by mounting the pair of leads 711 and 712 directly on a wiring board, for example, by soldering, the LED 71 can be configured to emit light in a horizontal direction. The light can be thus emitted in a direction parallel to the bottom surface of the box body H upon automated mounting. [0048] The side-view LED 71 has a configuration whose top view is illustrated in Fig. 3A and whose side view is illustrated in Fig. 3B. Fig. 3B shows angles of divergence. In particular, referring to Fig. 3A, the pair of leads 711 and 712 formed of lead frames or the like are secured, for example, by light-shielding resin 715 such that first ends thereof are exposed to an inner recess, and second ends thereof are led to the outside. An LED chip 713 is bonded to, and a wire 714 is connected to the first ends of the pair of leads 711 and 712 exposed to the inner recess. The periphery of the LED chip 713 and the wire 714 is secured by light transmissive resin 716 containing a luminescent color converter. The LED chip 713 is formed to emit blue light or ultraviolet light. The luminescent color converter contained in the light transmissive resin 716 converts the blue light or ultraviolet light into red and green (complementary color) light, or red, green, and blue light, and mixes the converted light to emit white light. Although the LED 7 that emits white light is likely to be varied in chromaticity due to the influence of resin or the like, though described later in detail, the embodiment of the present invention has a configuration in which light of at least two LEDs 7 are mixed instead of a configuration in which a single LED 7 irradiates a given portion with light. Thus, with this embodiment, the variation in chromaticity and brightness can be equalized. The second ends of the leads 711 and 712 exposed to the outside are directly connected and fixed to the wiring board by soldering or the like, so that the LED 7 emits light in the direction parallel to the wiring board, as described above. [0049] As described above, in the side-view LED 71, the LED chip 713 is covered with the light transmissive resin 716 containing the luminescent color converter. The side- view LED 71 has no lens portion, and is merely surrounded by the light-shielding resin 715 that secures the leads 711 and 712 for holding the LED chip 713. Hence, referring to Fig. 3B, the angle of divergence of the LED 71 is wide as in a range of from about 120° to 150°. When the light from the LED 71 is introduced into the box body 11 from the corner portions of the box body 11, the light can be emitted to the substantially entire area in the box body 11 as shown in Fig. 3B. Also, as described above, the side-view LED 71 is surrounded by the light-shielding resin 715. Hence, the light-emitting surface at the front surface is a portion of the light transmissive resin 716 containing the luminescent color converter, the portion which is indicated by oblique lines in Fig. 3A. Thus, the light is not emitted from the side surfaces of the LED 71.

[0050] The LED 7 is not limited to the side-view LED 71. Referring to Fig. 3C, the LED 7 may be an LED in which an LED chip 723 is mounted on a lead 721 and the periphery of the LED chip 723 is covered with light transmissive resin 725. Alternatively, referring to Figs. 3D to 3E, the LED 7 may be an LED in which an LED chip 743 is mounted on an insulating substrate 745, and the periphery of the LED chip 743 is covered with light transmissive resin 746. Still alternatively, though not shown, the LED 7 may be a dome (shell) LED in which an LED chip is mounted in a recess located at a first end of a lead, and the periphery of the LED chip is covered with resin to be formed into a dorm shape, or may be an LED having a lens portion at an end. When an LED 7 is configured to emit light in a direction perpendicular to the mounting surface of the LED 7, referring to Fig. 3F, leads 721 and 722 of an LED 72 are inserted into and fixed to a mounting substrate 76, and the mounting substrate 76 is fixed to a wiring board 24. When the dorm LED or the LED having the lens portion is employed and when the LED has a narrow angle of divergence, this embodiment may be applied to such an LED although the advantage of the protruding portion Hh of this embodiment is reduced. However, when the LED having a narrow angle of divergence is used, it is difficult to irradiate the entire area in the box body 11 with light. Hence, LEDs 7 may be desirably fixed after irradiation directions are adjusted such that each of the LEDs 7 mainly irradiates a half of the entire area of the box body 11 with light when the entire area is divided at a diagonal line.

[0051] The LED 72 shown in Fig. 3C, referring to a cross- sectional view and a perspective view of lead portions, is formed such that the two leads 721 and 722 formed of lead frames or the like are bent into angular C shapes, the LED chip 723 is mounted on a flat portion of one of the leads 721 and 722, a pair of electrodes of the LED chip 723 are electrically connected to the two leads 721 and 722 by a wire 724 or the like, and the vicinity of these portions is molded with the light transmissive resin 725. The periphery of the LED chip 723 that emits blue light or ultraviolet light may be covered with resin containing a luminescent color converter so as to convert the blue light or ultraviolet light into white light, in a manner similar to the example described above.

[0052] Chip LEDs 74 and 75 shown in Figs. 3D and 3E have a configuration in which a pair of terminal electrodes 741 and

742 are formed at both ends of an insulating substrate 745, an LED chip 743 is electrically connected to the pair of terminal electrodes 741 and 742 by a wire 744, a conductive adhesive, and the like. Also, the periphery of the LED chip

743 is covered with light transmissive resin 746. The example shown in Fig. 3E is the LED 75 having a reflective structure in which a reflection wall 747 is provided to surround the light transmissive resin 746. With such a configuration, the angle of divergence of light can be reduced to a certain degree (about 120°) . It is noted that, regarding Figs. 3D and 3E, like numerals refer like portions, and the description of the similar portions is omitted. [0053] In the example shown in Figs. IA to 1C, while a single LED 71 is provided at each of the four corners of the box body 11, two LEDs 71 may be preferably provided at each of the four corners. Accordingly, the brightness can be further increased. Also, when the LEDs 71 are varied in luminescent color and brightness, the unevenness of the luminescent colors and brightnesses can be efficiently equalized. To attain this, the holes Hd are formed separately at adjacent side walls Hc near the corner portions, instead of being provided to extend across the two adjacent side walls Hc at the corner portions as shown in Fig. IA. The LEDs 7 are respectively arranged outside the holes Hd and are fixed in directions to irradiate the entire inner space of the box body H with light. Hence, the light of the LEDs 7 can be mixed in the box body 11. When the directivity of each LED 7 is narrow, two LEDs 7 may respectively irradiate different half areas of the box body H with light, in a manner similar to the example described above .

[0054] When the directivity of each LED 7 is wide, the LED 7 does not have to irradiate the entire inner space of the box body 11 with light from the corner portion of the box body 11. The LED 7 may be provided at the bottom surface at a center portion of a side of a rectangle. This example is shown in Figs. 4A and 4B, which are a plan view and a side view similar to Fig. IA. This example is different from the example shown in Fig. IA only for the positions of the LEDs 7, and are similar for other portions such as the protruding portions Hh. Like numerals refer like portions and the description of the similar portions is omitted. [0055] When the configuration shown in Figs. IA to 1C is used and an 80-mm-square surface light source unit 1 is formed by using four LEDs 71 whose input is, for example, 0.057 W, the brightness thereof is about 500 cd at the front surface while the surface light source unit 1 is provided with the light-diffusing member 13. When a 100-mm-square surface light source unit 1 is formed with the same LEDs 71, the brightness is about 400 cd. When a 100-mm-square surface light source unit 1 is formed by using LEDs 71 whose input is 1 W, the brightness is 2000 cd. As described above, the size of the box body 11 can be determined depending on a desired brightness or the output of the LED. When the LED is operated by pulse driving or alternate-current driving, the LED seems to emit light as a result of an accidental image even when the LED does not actually emit light. The life of the LED can be increased irrespective of the brightness, and hence, the electric power can be saved. [0056] To manufacture such a surface light source unit 1, for example, an LED 7 is mounted on and connected to a wiring board 24, and a box body 11 which is formed by bending a punched plate as shown in Fig. 2B is mounted thereon and is fixed to the wiring board 24. Merely with this process, the surface light source unit 1 in which the box body 11 is combined with the LED 7 can be formed. The shape of the surface light source unit 1 in plan view (the shape of the box body 11 in plan view) does not have to be a rectangle. For example, a large surface light source can be provided when the shape is a polygon in plan view, such as a triangle or a hexagon.

[0057] When a plurality of surface light source units 1 shown in Figs. IA to 1C are arrayed in a matrix form to provide a large surface light source, irradiation regions shown in a side view become regions shown in Fig. 5A. Light of the LED 7 having a large angle of divergence and propagating directly upward is shielded by the protruding portion Hh, is reflected toward the bottom surface of the box body 11, is irregularly reflected in the inner space of the box body 11, and then is emitted to the outside. Hence, the light with the angle of divergence of about 60° (30° with respect to the bottom surface) directly diverges to an area above the side walls Hc. Accordingly, the light from the surface light source unit 1 is mixed with light from an adjacent surface light source unit 1. The area above the side walls lie tends to exhibit a low brightness, however, the area can exhibit a high brightness because the light from the surface light source unit 1 is mixed with the light from the adjacent surface light source unit 1, and the light reflected by a top portion of the side wall lie is closest to the front surface, that is, the light-diffusing member 13. (The brightness is inversely proportional to a square of a distance from the light source (irregularly reflecting portion) .) Thus, the in-plane brightness can be easily equalized upon adjustment of the height and inclination angle of the side walls lie. In an area located above the upper surface of the box body 11 by a distance of 5 mm or larger, light from the LED 7, reflection light from the inner surfaces of the box body 11, and light from the adjacent surface light source unit 1 are mixed. Hence, the brightness substantially equivalent to the brightness in a center portion can be obtained. In an area located above the upper surface of the box body 11 by a distance (E) of 5 to 30 mm, the area as well as a joint area can exhibit a substantially equalized brightness. To reduce a difference between brightnesses at the joint portion, the side walls of the box body 11 may have different heights, and a higher wall may be attached to a lower wall at the joint portion of these walls. Thus, the width of the side walls at the joint portion can be reduced.

[0058] The distance, at which the brightness is substantially equalized, from the upper surface of the box body corresponds to a secondary diffusion region located above the box body 11 where the light is diffused. The distance is preferably small to achieve a thin surface light source. The distance may be adjusted in accordance with the angle and height of the side walls lie of the box body 11, the directivity of the LED 7, and the like. When the brightness is equalized at a distance ranging from 5 to 30 mm, since the height of the box body 11 ranges from 10 to 20 mm as mentioned before, the entire height may become 50 mm or smaller, thereby being markedly thin. Regarding the adjustment of the side walls, the height of the side walls may be in a range of from about 5 to 25 mm, more particularly, about 5 to 20 mm (the entire thickness (C + E) including a height C of the box body 11 (primary diffusion reflection) is in a range of from 15 to 50 mm) . Fig. 5B schematically illustrates a state where light is irregularly reflected by a light-irregularly-reflecting member in the box body 11 (primary diffusion state) . In particular, as described above, since the surface of the light-irregularly- reflecting member has irregularities, light toward the bottom surface propagates while being irregularly reflected by the bottom surface in various directions. Hence, the light is mixed with light from other LEDs 7. When the light-diffusing member 13 (for example, a light-diffusing plate, a prism sheet, which is a material for condensing light to increase the brightness, or a liquid crystal panel or a sign display panel which is directly provided) is arranged at the position at a distance E corresponding to the secondary diffusion region, a display device such as a liquid crystal display device or an illuminated signboard can be provided. An image can be displayed with a uniform brightness .

[0059] An embodiment of an illuminated signboard is described as an example of a large surface light source using a plurality of arrayed surface light source units. Figs. 6A and 6B are a plan view and a cross-sectional view showing the illuminated signboard while a display panel, a light-diffusing plate, and the like, are omitted. [0060] Referring to Figs. 6A and 6B, a light source of the illuminated signboard employs a surface light source arranged such that a plurality of surface light source units 1 shown in Figs. IA to 1C are arrayed in a matrix form in a case 2 formed of, for example, an aluminum frame. For example, as shown in Fig. 7 in a fragmentary enlarged manner, the surface light source units 1 and a wiring board 24 are collectively fixed by a resin rivet 25, in which a detent is formed in a through hole at a bottom plate 23 formed of a composite plate and fixed to the bottom of the case 2. For the fixing, the rivet hole lie shown in Figs. IA and 2B is used. With this configuration, as long as a necessary resistance and wiring are formed at the wiring board 24, the LED 7 can be easily connected to a power source merely by fixing the surface light source unit 1 with the use of the resin rivet 25, and by connecting the leads of the LED 7. [0061] With the fixing using the resin rivet 25 or the like, the surface light source unit 1 can be fixed so as not to move, and also, the surface light source unit 1 may be easily detached if the LED 7 or the like fails and the LED 7 has to be replaced. Thus, the LED 7 can be easily replaced. [0062] To obtain an illuminated signboard with such a surface light source, although the configuration is similar to a typical signboard, a light-diffusing plate 3, a display panel 4 with an image, and a transparent cover 5 are placed on a supporting member 21 of the aluminum case 2 at a distance E (see Fig. 7) of about 5 to 30 mm from the upper surface of the surface light source unit. Then, a pressing member 22, which is rotatably attached to the aluminum case 2, fixes the light-diffusing plate 3, the display panel 4, and the transparent cover 5 to the aluminum case 2. With this configuration, the display panel 4 or the like can be easily replaced, and the surface light source unit 1 or the like can be easily repaired.

[0063] The light-diffusing plate 3 has a thickness of about 3 mm, and is a translucent plate member formed of so- called translucent acryl, such as opaque white acrylic resin (PMMA), polyethylene terephthalate (PET), polycarbonate, or glass. Even when light is obliquely incident on the light- diffusing plate 3, the light-diffusing plate 3 emits light in various directions in an equalized manner at the front surface. The thickness of the light-diffusing plate 3 is preferably increased, so that the light-diffusing plate 3 more effectively eliminates the directivity of light which is obliquely incident on the light-diffusing plate 3 from the lower surface. However, a light-diffusing sheet such as a thin vinyl sheet (FF sheet), or a translucent sheet may be used as long as the unevenness of the light from the lower surface of the light-diffusing member 13 can be almost eliminated. Alternatively or additionally, a prism may be provided instead of the light-diffusing plate 3, or onto the light-diffusing plate 3. Accordingly, the surface brightness can be substantially doubled.

[0064] The display panel 4 has an image to be displayed, such as a character or a figure. The image is provided on a transparent film sheet with colors by printing. When the display panel 4 is illuminated from a back surface thereof by lighting, the display panel 4 vividly displays the image. A transparent cover 5 is superposed on a front surface of the display panel 4 to protect the display panel 4. The transparent cover 5 is formed of a acrylic plate or a glass plate in a film-like form or with a thickness of several millimeters .

[0065] With this configuration, to fabricate an A2-size illuminated signboard with dimensions of 57 cm (length) x 41 cm (width) , when an illuminated signboard includes 10-cm- square surface light source units 1 with a single LED provided at each corner portion, and a surface light source includes LEDs by the number of 6x4 = 24 (power consumption of 5.5 W for the whole LEDs), the illuminated signboard with the brightness of about 400 cd is obtained. When an illuminated signboard includes 8-cm-square surface light source units 1, and a surface light source includes LEDs by the number of 7x5 = 35 (power consumption of 8 W for the whole LEDs), the illuminated signboard with the brightness of about 500 cd is obtained. When an illuminated signboard includes 10-cm-square surface light source units 1 with two LEDs provided at each corner portion to form a A2-size illuminated signboard with a high brightness, the power consumption is 11 W and the brightness is about 700 cd. When an illuminated signboard includes 8-cm-square surface light source units 1 (extra-high brightness), the power consumption is 16 W and the brightness is about 900 cd. The brightnesses of these examples each have unevenness of 10% or less in the entire area. A known illuminated signboard requires two 20-W fluorescent lamps to form an A2-size signboard with a brightness of about 800 cd. Therefore, the embodiment can provide the brightness similar to the known configuration with the power about one-fourth the power of the known configuration.

[0066] The LED with the directivity is used, and the light of the LED is evenly dispersed by reflection in the box body, so that light with a high intensity is irregularly reflected by the box body with a small height. Accordingly, the distance between the light source and the display panel can be markedly small. The light is not wasted, and is efficiently utilized. Also, since the distance between the light source and the display panel can be markedly small, the display panel can be configured with the entire thickness (distance from the bottom surface to the upper surface of the case 2) of about 45 mm.

[0067] In the above examples, the surface light source units shown in Figs . IA to 1C are arrayed without a gap to form the surface light source, and the surface light source is applied to the illuminated signboard. Depending on the purposes of use, a signboard may be used to vividly provide a simple display by lighting for advertisement in the street at night, or to display simple, large, spaced apart characters such as Japanese Katakana characters. In such a case, the thickness is not necessarily reduced, and the display effect is not changed even when the brightness is slightly reduced in a dark environment. Hence, the brightness can be substantially equalized at the position of the light-diffusing member 13 by increasing the distance between the plane of opening of the surface light source unit 1 to the light-diffusing member 13, even though the surface light source units 1 are arrayed with a gap. [0068] In particular, the inventor of the present invention searched for a distance between the surface light source unit 1 and the light-diffusing member (plate) 13, to achieve substantially equalized in-plane brightness, by changing the distance between the surface light source unit 1 and the light-diffusing member 13. An 80-mm-square surface light source unit 1 (the upper surface A or the plane of opening shown in Fig. 1C is a square with a side of 80 mm) with two LEDs provided at each of four corner portions, or eight LEDs in total (the output per LED is 0.057 W), was used. It is assumed that b is a distance between the planes of opening (upper surfaces) of the surface light source units 1, a is a distance between the surface light source unit 1 and the case 2, p is a pitch of an array of the surface light source units 1, and h is a distance between the bottom surface of the surface light source unit 1 and the light-diffusing member 13 (the height C of the surface light source unit 1 is 15 mm) . In relation to the change in the value b, Table 1 shows the value h when the brightness is substantially equalized at the front surface of the light-diffusing member 13, which is formed of a light-diffusing plate of translucent acryl with a thickness of 3 mm, and shows the brightness at the front surface of the light-diffusing member 13. The inner surface of the case 2 is coated with white painting with high reflectivity. As shown in Fig. 9, when the array is rounded, the relationship between the distance b and the distance to the light-diffusing member 13 becomes similar to that in Table 1.

Table 1: Relationship between distance b of light source units and distance h to light-diffusing member

[0069] As shown in Table 1, when the same surface light source units 1 are used, the pitch thereof is increased, and a space is provided between the surface light source units 1, the brightness can be substantially equalized as long as the distance between the surface light source unit 1 and the light-diffusing member 13 is increased although the brightness at the front surface of the light-diffusing member 13 is decreased. For example, when the occupied area of the signboard is not particularly limited, or when the display does not have to be particularly bright, such as when the surface light source unit 1 is used for the advertisement in the street at night, the surface light source units 1 may be arrayed with a gap depending on the purpose of use.

[0070] Also, as for the purpose of advertisement in the street, for example, simple characters are arranged at a predetermined gap and only the shapes of the characters are lit and displayed, unlike a generally used illuminated signboard in which a fine image is displayed by a backlight. In such a case, for example, as partly shown in a plan view of Fig. 9A, the plurality of surface light source units 1 are arrayed at a predetermined gap along the shapes of characters or the like, and the light-diffusing member 13 (e.g., a translucent acrylic plate with a thickness of 3 mm) is provided at a height shown in Table 1 depending on the distance b. Accordingly, desired characters or the like can be displayed with a substantially uniform brightness. In particular, the light-diffusing plate or the like is provided in a display region of the characters or the like, and the surface light source units 1 are provided on the side of the bottom surface of the light-diffusing plate. [0071] When the surface light source unit 1 shown in Fig. 9 is installed at an advertising tower or the like in the street, referring to Figs. 1OA and 1OB, the surface light source unit 1, together with the wiring board 24 and the LED 7, are covered and sealed with a case 81. The case 81 is, for example, a plastic case formed of an acrylic plate, or a light transmissive material, and is provided at least on the side of the plane of opening of the surface light source unit 1. Power connection means such as a cord 83 is led to the outside from the surface light source unit 1. With this configuration, a surface light source 8 may be merely attached in a display region where a desired character or the like is displayed. Accordingly, the signboard does not have to be entirely sealed even when the signboard is installed at a location in the street, where rain may be expected, and the attachment is very simple. Referring to Fig. 1OA, reference numeral 82 is an attachment tag for the attachment of the surface light source 8 to the display region or the like.

[0072] The present invention is applicable to a backlight for a liquid crystal display device such as a large-screen liquid crystal television, or is applicable to an illuminated signboard, for example, in a station, a public square, or an exhibition hall.

[0073] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.

Claims

1. A surface light source unit, comprising: a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light-reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward; and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body, wherein protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls.

2. The surface light source unit according to claim 1, wherein each of the protruding portions has a length at a center portion thereof so that the protruding portion shields light emitted from an upper edge of a light-emitting surface of the corresponding light-emitting device at an angle of 40° or larger with respect to a horizontal plane, and so that the protruding portion does not shield light emitted at an angle of 20° or smaller.

3. The surface light source unit according to claim 1 or 2, wherein the protruding portions are formed such that cut portions for forming the holes at the side walls of the box body are partly bent.

4. The surface light source unit according to any of claims 1 to 3, wherein the box body has a rectangular shape in plan view, and wherein the light-emitting devices are provided at four corners of the box body, or at center portions of four side walls of the box body.

5. A surface light source, comprising: a surface light source unit including a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light-reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward, and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body, wherein protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls; and a case made of a light transmissive material, wherein at least a plane-of-opening side of the box body is covered with the case, and wherein power connection means is led to the outside from the case.

6. A surface light source, comprising: a plurality of arrayed surface light source units, each of the surface light source units including a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light-reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward, and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body, wherein protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls; and a light-diffusing member provided to cover the plurality of surface light source units.

7. An illuminated signboard, comprising: a surface light source including a plurality of arrayed surface light source units, each of the surface light source units having a tray-shaped box body, a bottom surface thereof being a polygon with three or more corners, an upper surface thereof being open, a light-reflecting member being provided on an inner surface thereof, side walls thereof being inclined outward, and semiconductor light-emitting devices arranged at positions outside holes formed at least at two positions of the side walls near the bottom surface of the box body, so as to emit light toward an inner space of the box body, wherein protruding portions are formed at upper sides of the holes formed at the side walls, so as to extend from the side walls; and a light-diffusing member and a display panel provided on a front surface side of the surface light source at a predetermined distance from the front surface of the surface light source.