Surface illumination method using point light source, linear light source device, and surface illumination device using linear light source device

A surface illumination device includes: a point light source I having high directionality; a linear light conversion unit II that converts light from the point light source into linear light; a linear light diffusion unit III that diffuses the linear light; and a surface lighting unit IV that is irradiated with diffused light and outputs surface light. The light from the point light source I is converted into the linear light by the linear light conversion unit II. The linear light thus converted is diffused in a predetermined direction by the linear light diffusion unit III. The diffused light is radiated on the surface lighting unit IV to be converted into surface light and radiated.

RELATED APPLICATIONS

This application is a nationalization under 35 U.S.C. 371 of PCT/JP2010/065630, filed Sep. 10, 2010, and published as WO 2011/030856 A1 on Mar. 17, 2011, which claims priority to Japanese Patent Application Serial No. 2009-211131, filed Sep. 11, 2009, which applications and publication are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a surface illumination method using a point light source, a light source device, and a surface illumination device using the light source device. More particularly, the invention relates to a surface illumination method of converting light from a point light source into linear light, then converting the linear light into surface light, and radiating the surface light, to a light source device that converts the light from the point light source into the linear light and radiates the linear light, and to a surface illumination device using the light source device.

BACKGROUND ART

In recent years, instead of a conventionally used fluorescent light and the like, a light emitting diode (hereinafter referred to as LED) and a laser diode (hereinafter referred to as LD) consuming less electricity and having a longer service life and smaller size compared with the fluorescent light and the like have begun to be used as a light source for a surface illumination device such as a liquid crystal display backlight device.

For example, Patent Document 1 listed below describes an edge light type lighting device using an LED. The lighting device includes the LED, a light guide plate comparable in size to a post card and having a light guide portion for light from the LED formed as a flat surface, and a reflecting mirror that reflects light from the LED, and is configured in such a manner that the LED is mounted on the flat surface of the light guide plate and covered by the reflecting mirror. Patent Document 2 listed below describes a lighting device in which light from an LED is guided to a light guide plate through a light source rod including a prism array. Patent Document 3 listed below describes a cash register guide lamp in which a plurality of LEDs are disposed at equal intervals on a light input surface of a light guide body, light from the LEDs is irregularly reflected by a reflector body, and the diffused light makes a light output surface of the light guide body emit surface light to illuminate a display body opposed to the light output surface of the light guide body.

While the lighting devices described above are of the edge light type, a direct type lighting device is also known. For example, Patent Document 4 listed below describes a surface light emitting device in which an LED is provided with a light controller that controls light from the LED so that surface light can be obtained. Patent Document 5 listed below describes a surface lighting light source device and a surface illumination device using the surface lighting light source device. The surface lighting light source device includes: an LED; a box-shaped casing including a bottom surface portion in which the LED is mounted at the center portion and side surface portions standing from a periphery of the bottom surface portion, and being provided with an opening formed on a side opposite to the bottom surface portion; and an optical reflector plate that covers the opening and substantially uniformizes the light from the LED. The surface illumination device uses the plurality of surface lighting light source devices that are connected to each other.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In all of the edge light type lighting devices in Patent Documents 1 to 3 described above, one of or a plurality of LEDs is disposed on one or all sides of the rectangular light guide plate. Thus, uniform illumination light can be obtained from a light guide surface. These lighting devices, however, require the light guide plate that is relatively expensive and has a predetermined thickness and size and thus are difficult to be formed with a larger size. For example, the lighting device in Patent Document 1 described above uses a glass or acrylic plate comparative in size to a post card and thus is difficult to be formed with a size larger than that. Providing the larger size by all means requires a large light guide plate. In addition, a plurality of light emitting diodes are required as in the lighting device in Patent Document 3 described above and the plurality of light emitting diodes need to be disposed on light receiving surfaces on all sides of the light guide plate. Thus, the weight of the lighting device is increased, the number of parts is increased to make the assembling cumbersome, and further a cost is increased. Furthermore, when such a large light guide plate is used, a light path between the light source and a light emitting surface is long and thus, light is largely attenuated. Therefore, uniform illumination light is difficult to obtain and illumination light with high intensity is also difficult to obtain. These edge light type lighting devices each use the light guide plate and light sources are disposed around the light guide plate. Thus, the edge light type lighting device is suitable as a small lighting device but the size thereof is hard to increase. In contrast, the direct type surface illumination devices in Patent Documents 4 and 5 use no light guide plate and thus can have a light weight. Still, a plurality of light source devices need to be arranged in matrix to obtain illumination light with a large area and thus has a problem with the high cost.

Thus, the present invention is made to solve the problems of the conventional techniques, and an object of the present invention is to provide a surface illumination method of converting light from a point light source into surface light with a large area and radiating the surface light.

Another object of the resent invention is to provide a surface illumination device that can obtain uniform surface illumination light with a large area without using a light guide plate that is an essential element in the conventional techniques even when a point light source having high directionality is used as a light source.

Means for Solving the Problems

The object is achievable with the following structures.

A surface illumination method using a point light source that uses the point light source having high directionality, a linear light conversion unit that converts light from the point light source into linear light, a linear light diffusion unit that diffuses the linear light, and a surface lighting unit that is irradiated with diffused light and outputs surface illumination light, the method includes: converting the light from the point light source into the linear light by the linear light conversion unit; diffusing the linear light obtained by the conversion in a predetermined direction by the linear light diffusion unit; and radiating the diffused light on the surface lighting unit to be converted into surface light and radiating the surface light.

In the surface illumination method of the present invention, the point light source may be a light emitting diode or a laser diode.

A linear light source device of the present invention for achieving the object includes a point light source having high directionality and a casing that accommodates therein the point light source. The casing is formed of a box-shaped body having a thin and long bottom plate in which the point light source is provided at a substantially center portion, side plates standing to a predetermined height from a periphery of the bottom plate, a side defining an opening provided facing the bottom plate, and an inner wall surface that includes a reflective surface, the opening being covered by an optical reflector plate provided with a radiation pattern through which the light from the point light source is output as linear light.

In the linear light source device of the present invention, it is preferable that the casing be formed of a long cylindrical body having a predetermined diameter and an inner wall surface formed of a reflective surface, the point light source be fixed at a substantially center portion of the cylindrical body, and a slit be formed, on a ceiling portion substantially right above the point light source, through which the linear light is emitted and extending in a longitudinal direction passing through the right above ceiling point.

In the linear light source device of the present invention, the point light source may be a light emitting diode or a laser diode.

In the linear light source device of the present invention, it is preferable that the casing include any one of a reflective material made of a laminated body of ultrafinely foamed light reflector agent and aluminum metal, a reflective material having a reflective layer including polytetrafluoroethylene on a surface, and a reflective material having a reflective layer including barium sulfate on a surface.

A surface illumination device of the present invention for achieving the object includes: a point light source having high directionality; a linear light conversion device that converts light from the point light source into linear light; a linear light diffusion device that diffuses the linear light from the linear light conversion device; and a surface illumination light emitting member that is irradiated with diffused light from the linear light diffusion device and outputs surface light.

In the surface illumination device of the present invention, the point light source may be a light emitting diode or a laser diode.

In the surface illumination device of the present invention, it is preferable that the linear light conversion device include a casing that accommodates therein the point light source, the casing be formed of a box-shaped body having a thin and long bottom plate in which the point light source is mounted at a substantially center portion, side plates standing to a predetermined height from a periphery of the bottom plate, a side defining an opening provided facing the bottom plate, and an inner wall surface that includes a reflective surface, the opening being covered by an optical reflector plate provided with a radiation pattern through which light from the point light source is output as linear light, the linear light diffusion device include a space having a size large enough to accommodate the linear light conversion device and a diffusion member on an outer wall surface diffusing the linear light from the linear light conversion device in a predetermined direction, the surface illumination light emitting member be formed of a diffusion plate that is irradiated with the diffused light from the linear light diffusion device and outputs surface light.

In the surface illumination device of the present invention, it is preferable that the diffusion member be provided with a linear light diffusion pattern with which a portion irradiated with radiated light radiated with an angle θ of 60 degrees between a center light axis of the linear light and the center light axis has a high light reflectance and low light transmittance and a portion farther from the 60-degree angle has a lower light reflectance and higher light transmittance.

Effect of the Invention

By the surface illumination method of the present invention, the point light from the point light source having high directionality can be converted into the surface light with a large area to be illuminated.

With the linear light source device according to the present invention, the linear light source device that converts the point light from the point light source into the linear light can be obtained.

The linear light source device according to the present invention can be used for a germicidal lamp for water, curing an adhesive resin, a backlight of a light emitting liquid crustal display, and the like.

In the surface illumination device according to the present invention, the point light from the point light source is converted into the linear light, the linear light obtained by the conversion is diffused in a predetermined direction, and thus surface illumination light with a large area can be obtained from the surface illumination light emitting member.

In the surface illumination device according to the present invention, the diffusion plate is irradiated with the linear light output from the linear light conversion device by uniform light intensity through the predetermined linear light diffusion pattern.

The surface illumination method, the linear light source device, and the surface illumination device according to the present invention do not form a bright spot at the center portion nor conversely make a portion right above the point light source having high directionality dark even when the point light source having high directionality such as the LED or the LD is used, and thus uniform illumination light can be obtained.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below. It should be noted that the embodiments described below exemplify a surface illumination method using a point light source, a light source device, and a surface illumination device using the light source device for embodying the technical idea of the present invention and thus are not intended to limit the present invention to the embodiments. The present invention can be equally applied to other embodiments included in a scope of claims. In the embodiments, a linear light conversion device, a linear light diffusion device, and a surface illumination device include a single linear light conversion device (light source device). Alternatively, the linear light conversion device, the linear light diffusion device, and the surface illumination device may include a plurality of linear conversion devices connected in tandem in a longitudinal direction.

A surface illumination method using a point light source according to a first embodiment of the present invention will be described with reference toFIG. 1.FIG. 1is a schematic explanatory diagram for explaining the surface illumination method using the point light source according to the first embodiment of the present invention.

This surface illumination method is a method of converting light from the point light source into linear light, converting the linear light obtained by the conversion into surface light, and radiating the surface light. Specifically, as illustrated inFIG. 1, the surface illumination method uses a point light source I having high directionality, a linear light conversion unit II that converts the light from the point light source into the linear light, a linear light diffusion unit III that diffuses the linear light, and a surface lighting unit IV that is irradiated with the diffused light and outputs the surface illumination light to convert the light from the point light source I, i.e., point light, into the linear light by the linear light conversion unit II, diffuse the linear light obtained by the conversion in a predetermined direction by the linear light diffusion unit III, and radiate the diffused light on the surface lighting unit IV and illuminate the surface light. Concrete examples of the linear light conversion unit, the linear light diffusion unit, and the surface lighting unit used in the surface illumination method will be described below.

A point light source1uses a single LED or an LED including a group of a plurality of LED elements (hereinafter, these are collectively referred to as LED) or an LD. The LED is not limited to those emitting light's three primary colors of R, G, and B. An LED emitting other colors may be used. In addition, an LED or an LD provided with a lens may be used. In the embodiments, an example where the LED is used will be described.

As depicted inFIG. 1, the LED1has substantially spherical light distribution characteristics that light is radiated in 360 degrees from a light emission point or a light emission surface of the LED1and converges at a point apart from the light emission point or the light emission surface. Specifically, as depicted in I-1inFIG. 1, light from the LED1has a light distribution curve denoted by a reference symbol A in a range that is defined by: the light emitting center point (surface)0of the LED1; a predetermined distance apart from the light emitting point (surface)0in a horizontal direction; a vertical line of 0 degree (0°) passing through the center point; and space specified with angle of 0° to 90° for the perpendicular line. While the light distribution curve A will be drawn as a ball shaped curve extending in a radiation direction, i.e., 360 degrees, around the light emission center point (surface)0, the light passing through a light axis Ax at a directivity angle of 0 degree has the highest intensity.

The LED1is point light having the light distribution characteristics as depicted in I-1inFIG. 1. Thus, when the LED1is directly used for illumination light, a range that can be illuminated is extremely narrow and surface illumination light with a large area cannot be obtained. Thus, before obtaining the surface illumination light with a large area, the point light from the LED1is converted into narrow and long linear light. The conversion into the linear light is performed by using the liner light conversion unit II, specifically a linear light conversion device2as illustrated inFIG. 2.

The linear light conversion device will be described with reference toFIG. 2.FIG. 2Ais an external perspective view of the linear light conversion device andFIG. 2Bis an exploded perspective view of the linear light conversion device inFIG. 2A.

The linear light conversion device2includes: the LED1; a box-shaped casing3including a thin bottom plate3ain which the LED1is fixed at a substantially center portion and side plates3bstanding to a predetermined height from a periphery of the bottom plate3a, and being provided with an opening3odefined by top portions of the side plates3b; and an optical reflector plate4covering the opening3o. The LED1is fixed at the substantially center portion of the bottom plate3aand the optical reflector plate4covers the opening3o.

The bottom plate3aof the casing3has a pair of opposing long sides and a pair of opposing short sides. For example, a length L1of the long side and a length L2of the short side are 200 mm and 10 mm, respectively. A height H of the side plate is 10 mm for example. An inner wall surface of the box-shaped casing3is formed of a reflective surface having a high reflectance. A mounting hole in which the LED1is mounted is formed at the substantially center portion of the bottom plate3a. The LED1is fixed on a substrate having a predetermined size. The substrate is disposed on a back surface of the bottom plate in such a manner that a light emitting portion of the LED is exposed through the mounting hole. The casing3is formed of a reflector plate material, e.g., an ultrafinely foamed light reflector plate, with a high light reflectance, a low light transmittance, and a low light absorptivity. As the ultrafinely foamed light reflector plate, one having a reflectance of 98%, a light transmittance of 1%, and a light absorptivity of 1% is available and is preferably used. It is a matter of course that the casing is not limited to this material and a transparent substrate on which a reflective material is applied or printed may be used. For example, this may be formed by applying or screen printing a substance obtained by emulsifying particulates of titanium white, a substance obtained by emulsifying particulates of polytetrafluoroethylene, or the like.

As illustrated inFIG. 2, the optical reflector plate4is formed of a thin plate body having a sufficient size for covering the opening3oof the casing3and is formed of a reflector plate having a high light reflectance, a low light transmittance, and a low light absorptivity. The material used therefor is preferably the same with that used for the casing. The optical reflector plate includes a pair of long sides4aand4band a pair of short sides4cand4d. Lengths of the long side and the short side are the same with the lengths of the sides of the bottom plate3aof the casing3. On the optical reflector plate4, a center reflection portion5is formed at the center portion and outer reflection portions6are formed respectively toward the short sides4cand4don both ends from the center reflection portion. The center reflection portion5and the outer reflection portions6form a predetermined radiation pattern. The center reflection portion5is right above the LED1when the optical reflector plate4is mounted on the opening3oof the casing3and includes a center reflection area5afacing a portion vertically right above the light emitting portion of the LED and having a small area and center periphery reflection areas5bapart from the center reflection area5afor a predetermined distance and having a slightly larger area. Due to its light distribution characteristics, the LED1radiates light with the highest intensity to the center reflection area5aand light with second highest intensity to the center periphery reflection areas5b. Thus, such an adjustment is performed that the center reflection area5ahas the highest light reflectance and the lowest light transmittance and the center periphery reflection areas5bhave a slightly lower light reflectance and a slightly higher light transmittance. Since the center reflection area5ahas the highest light reflectance and the lowest light transmittance, this area can be prevented from being dark and generation of a bright illumination spot can be prevented as well.

The reflectance and the transmittance are adjusted in the processing of the reflector plate. For example, the thickness of the reflector plate at the center reflection area5ais adjusted while the reflector plate at the center periphery reflection areas5bis adjusted by being provided with a plurality of thin grooves (longitudinal groove, lateral groove, or ring-shaped half-cut groove) and the like.

The outer reflection areas6each include an intermediate outer reflection portion6aand an outermost reflection portion6bprovided toward both short sides4cand4dfrom the center periphery reflection area5b. The intermediate outer reflection portion6aand the outermost reflection portion6binclude a plurality of slits and through holes having different opening areas. Specifically, the intermediate outer reflection portion6aincludes slits61to67in which one disposed farther from the center periphery reflection area5bhas a larger opening area. The outermost reflection portion6bincludes through holes68to619in which one disposed farther from the intermediate outer reflection portion6ahas a larger opening area. In the outer reflection area6, the plurality of slits and openings formed in the intermediate outer reflection portion6aand the outermost reflection portion6bhave different opening areas. Specifically, the opening area becomes larger toward the outermost reflection portion6bfrom the intermediate outer reflection portion6a. Thus, the point light from the LED1can be substantially uniformly output as substantially linear light.

In the linear light conversion device2, the LED1is mounted on the bottom plate3aof the casing3and the opening3ois covered by the optical reflector plate4. Thus, the point light from the LED1is reflected once or multiply reflected between the inner wall surface of the casing3and the back surface of the optical reflector plate4(rear surface of the light output surface). As a result, the linear light with a predetermined width and length is radiated through the center reflection portion5and the outer reflection portions6of the optical reflector plate4(see II-1inFIG. 1). For example, the width and the length of the linear light radiated from the surface of the optical reflector plate4are 0.1 to 10 mm and 200 mm, respectively.

As depicted in II-2inFIG. 1, the light distribution characteristics of the linear light from the linear light conversion device2have a shape as if the ball shaped light distribution characteristics curve (see I-1inFIG. 1) of the LED1is cut in near-vertical directions. Thus, the linear light conversion device2can convert the point light from the LED1into the linear light having a predetermined width and length.

The linear light conversion device2, which is used as the linear light conversion unit that converts the point light from the LED1into the linear light in the description above, can radiate the linear light having a predetermined width and length and thus can also be used as a light source device. For example, the linear light conversion device2can be used as the light source device for a scanner.

While an ultrafinely foamed reflector plate material is used as a material for the optical reflector plate, the material is not limited thereto and a transparent substrate on which a reflective material is applied or printed at a portion excluding the opening may also be used. For example, this is formed by applying or screen printing a substance obtained by emulsifying particulates of titanium white, or a substance obtained by emulsifying particulates of polytetrafluoroethylene.

In the optical reflector plate4, the radiation pattern is formed by providing the center reflection portion5including the center reflection area5aand the center periphery reflection areas5bas well as the outer reflection potions6. The structure is not limited to this and may be changed.

Modifications of the optical reflector plate having different radiation patterns will be described with reference toFIG. 3andFIG. 4.FIG. 3AtoFIG. 3Care plan views of the modifications of the optical reflector plates.

An optical reflector plate4A includes a center reflection portion5A at its center portion and outer reflection portions6A respectively extending towards the short sides4cand4dat both ends from the center reflection portion (seeFIG. 3A). The center reflection portion5A includes a plurality of micro-pores so as to reflect the LED light with a high reflectance and have a low light transmittance. The outer reflection portion6A includes through holes having openings with which the outer reflection portion6A has reflectance gradually reduced and transmittance gradually increased, as it gets farther from the side center reflection portion.

An optical reflector4B includes a center reflection portion5B and outer reflection portions6B each having slits. The slits have different areas to have a predetermined aperture ratio (seeFIG. 3B). In an optical reflector4C, a center reflection portion5C includes no slit while outer reflection portions6C each includes a relatively long slit with an opening area increased as it extends in a longitudinal direction (seeFIG. 3C).

Other linear light conversion devices will be described with reference toFIG. 4andFIG. 5.FIG. 4A,FIG. 4B,FIG. 5A, andFIG. 5Bare perspective views of modifications of the linear light conversion device.

The shape of the casing3in the linear light conversion device2is not limited to a cuboid and may be shapes illustrated inFIG. 4. Specifically, in a linear light conversion device2A, side plates3Ab of a casing3A form a polygonal columnar shape, and in a linear light conversion device2B, a side plate3Bb of a casing3B forms a cylindrical shape. The shape of the casing is not limited those illustrated in the figures and may be of any shape as long as it is square columnar or cylindrical shape.

In a linear light conversion device2C, a pair of light convergence reflector plates a and b inclined by a predetermined angle α and opposed to each other with a predetermined distance provided between top portions stand from upper edges of opposing side plates3b. The distance is 0.1 to 2 mm for example. The light convergence reflector plates are preferably made of a material same as that of the optical reflector plate.

Even when relatively thick linear light having a width of about 5 mm to 10 mm is emitted from the optical reflector plate4, the linear light conversion device2C can convert the linear light into thin linear light having a width of about 0.1 to 2 mm.

In a linear light conversion device2D, a casing denoted by reference numerals7aand7bforming a long cylindrical body having a predetermined inner diameter and having an inner wall surface formed of a reflective surface stand on a bottom portion7con the casing. Thus, in this casing, the side surface portions and the optical reflector are integrally formed. The point light source1is fixed in a substantially center portion of the bottom portion7c. Slits8through which linear light is output is formed in a longitudinal direction passing through the ceiling point substantially right above the point light source1. A center portion8aof the slits is narrow, and outer potions8bof the slits are widened as it gets farther from the center portion8a.

The linear light diffusion device will be described with reference toFIG. 6andFIG. 7.FIG. 6is an external perspective view of the linear light diffusion device, andFIG. 7is an exploded perspective view of the linear light diffusion device inFIG. 6. As illustrated in III-1inFIG. 1andFIG. 6, the linear light diffusion unit III is formed of a linear light diffusion device9that covers the linear light conversion device2and diffuses the linear light from the linear conversion device in a predetermined direction.

The linear light diffusion device9exerts an effect of controlling light distribution of light emitted from the linear light conversion device2so as to uniformly light both surfaces or one of the surfaces of an edge type surface illumination device incorporating the linear light diffusion device9. The structure thereof will be described below. The linear light diffusion device9includes the thin rectangular fixing plate10on which the linear light conversion device2is fixed and a linear light diffusion member11curved into a semicircular shape or an arch shape from one of opposing side edges of the fixing plate10to the other side edge so as to have an inner space large enough to accommodate the linear light conversion device2. The fixing plate10is formed of a plate body having a sufficient size to allow the linear light conversion device2to be placed and fixed thereon. Specifically, the fixing plate10is formed of a plate body having a length substantially the same as the length of the bottom plate of the linear light conversion device2and a width slightly larger than the width of the bottom plate of the linear light conversion device2and is formed of a reflector plate having a high light reflectance, a low light transmittance, and a low light absorptivity. A material to form the fixing plate10is preferably the same as that of the casing of the linear light conversion device.

The linear light diffusion member11is formed of a reflector plate having a predetermined thickness, a length substantially the same as the length of the fixing plate10, and a width slightly larger than the width of the fixing plate10. Specifically, as illustrated inFIG. 7andFIG. 8, the linear light diffusion member11has a rectangular shape including a pair of opposing long sides11aand lib having a length substantially the same as the length of the fixing plate10and a pair of opposing short sides11cand lid having a length longer than the width of the fixing plate. The linear light diffusion member11is fixed on the fixing plate10while being curved and thus is preferably formed of a flexible material. The linear light diffusion member11is fixed on the fixing plate10while being curved, accommodates the linear light conversion device2in an internal space11o, and includes a plurality of through holes arranged in a predetermined pattern and having a predetermined opening areas for diffusing the linear light from the linear light conversion device in a predetermined direction.

The arrangement of the through holes provided in the linear light diffusion member11will be described with reference toFIG. 8.FIG. 8is a plan view of the linear light diffusion member forming the linear light diffusion device inFIG. 6illustrated in a flattened state.

The through holes are each formed of a hole having a rectangular opening and are formed at intersecting portions between virtual vertical lines X1, X2, X3. . . Xm-2, Xm-1, and Xm vertically extending from one of short sides, i.e. the short side11cto the other short side, i.e. the short side11dand drawn at substantially equal intervals and virtual horizontal lines Y1, Y2, Y3. . . Yk-2, Yk-1, and Yk horizontally extending from one of long sides, i.e. the long side11ato the other long side, i.e. the long side11band drawn at substantially equal intervals. For example, the through holes1211,1212. . .121n-1, and121nare formed at intersecting portions between the virtual vertical line X1and odd number lines, e.g., Y1, Y3. . . , of the virtual horizontal lines, and the through holes1221,1222. . .122n-2, and122n-1are formed at intersecting portions between the next virtual vertical line X2and even number lines, e.g., Y2, Y4. . . Yk-1, of the virtual horizontal lines. The through holes12m1to12mnare arranged in a similar manner. By being thus arranged, the through holes are arranged in a predetermined pattern to form a predetermined linear light diffusion pattern. The through holes are formed as holes having rectangular openings but the shape of the through holes is not limited to this and may be of any shape such as a circular shape and an elliptical shape.

The through holes arranged on each of the virtual horizontal lines Y1, Y2, Y3. . . Yk-2, Yk-1, and Yk have the same opening area while the through holes arranged on each of the virtual vertical lines X1, X2, X3. . . Xm-2, Xm-1, and Xm have different opening areas. The arrangement and the opening areas are for providing a function of irradiating a diffusion plate with the linear light radiated from the linear light conversion device2diffused uniformly as much as possible in consideration of the light distribution characteristics thereof so as to obtain uniform illumination light from the surface of the diffusion plate. Thus, the sizes and the pattern of the arrangement of the through holes are important. The sizes and the pattern of the arrangement of the through holes are determined with regard to the diffusion plate standing at a portion apart from the linear light conversion device2for a predetermined distance.

The sizes and the arrangement of the through holes will be described with reference toFIG. 8toFIG. 10.FIG. 9is a partial cross-sectional view of the surface illumination device incorporating the linear light diffusion device inFIG. 6.FIG. 10is an illumination curve in a case where the linear light diffusion device is removed from the surface illumination device inFIG. 9. The surface lighting unit IV is formed of a surface illumination device13including a pair of diffusion plates14A and14B irradiated with the diffusion light from the linear light diffusion device and illuminates with the diffusion light as surface light.

The diffusion plates14A and14B stand in parallel with each other from both sides of the linear light conversion device2with a predetermined distance provided therebetween. The diffusion plates14A and14B are each formed of a rectangular plate having substantially the same length as the long side of the linear light conversion device2and a predetermined height (e.g., 200 mm). The linear light conversion device2is positioned substantially in the middle of the pair of opposing diffusion plates14A and14B. Thus, if an angle subtended by the optical reflector plate4of the linear light conversion device2to a predetermined position Pθon one diffusion plate14B is θp, a distance from a center line Cx of the optical reflector plate4to the diffusion plate14B is d, a distance from the center line of the optical reflector plate4to the predetermined position Pθis r, a height from the optical reflector plate4to the predetermined position Pθis x, the following relationship holds true therebetween. Specifically,
cos θp=d/r
cos(90°−θp)=x/r
r=√(x2+d2).
An illuminance Eθat the point Pθis
Eθ=cos θp·cos(90°−θp)·K/r2.
Thus, from the formulae above, Eθcan be represented as
Eθ=K·d·x/r4.
Here, K is a proportional constant.
When Eθis differentiated by x as a function of x,

FIG. 10illustrates a curve drawn based on the formulae. As illustrated inFIG. 10and the formulae above, Eθis largest when θp=30°, i.e., when an angle between the center light axis of the linear light and the center light axis is 60°.

Specifically, the sizes of the through holes formed on the linear light diffusion member11should be set in such a manner that a through hole at a position where the angle subtended by the optical reflector plate4to the predetermined position Pθis 30° is the smallest. Uniform surface light can be obtained on the diffusion plate14B by setting the sizes of the through holes formed on the linear light conversion device2based on the formulae above for other angles. The same applies to the diffusion plate14A.

This relationship will be described with regard to the linear light diffusion member11illustrated inFIG. 8. The through holes disposed on the virtual horizontal lines Y3and Yk-2have the smallest opening area. The opening area of the through holes on a virtual horizontal line gradually increases as it gets farther from these virtual horizontal lines and the through holes on the center virtual vertical line Yc have the largest opening area.

In this surface illumination device, the point light from the LED1is converted into the linear light by the linear light conversion device, the linear light obtained by the conversion is diffused in a predetermined direction by the linear light diffusion device, and the diffused light is radiated on the diffusion plates and can be illuminated as the surface light.

In the linear light diffusion device9, the through holes are also formed near the virtual horizontal line Yc of the linear light diffusion member11. These through holes near the virtual horizontal line Yc may be omitted. A linear light diffusion member11A inFIG. 11has the through holes near the virtual horizontal line Yc omitted but other structure is the same as the linear light diffusion member11. By omitting the through holes near the virtual horizontal line Yc, the light emitted in the direction of the center axis of the linear light is efficiently reflected and a larger amount of light passes through the through holes to be emitted to the diffusion plates14A and14B.

A surface illumination device according to another embodiment of the present invention will be described with reference toFIG. 12andFIG. 13.FIG. 12is an external perspective view of a surface illumination device according to another embodiment of the present invention.FIG. 13is a cross-sectional view of the surface illumination device inFIG. 12taken along the line XIII-XIII.

As illustrated inFIG. 12andFIG. 13, a surface illumination device13has a structure in which a frame member15accommodates therein, an LED1, a linear light conversion device2in which the LED1is mounted, a linear light diffusion device9by which the linear light from the linear light conversion device2is diffused and output in a predetermined direction, and a pair of diffusion plates14A and14B. The frame member15is formed of a frame body of a frame shape including a bottom frame15ahaving a sufficient size for allowing the linear light diffusion device9and the pair of diffusion plates14A and14B to be accommodated, side frames15cand15dstanding from both ends of the bottom frame and having a sufficient height for allowing the pair of diffusion plates14A and14B to be accommodated, and an upper frame15bconnecting between top portions of the side frames, and being provided with a space15oinside. The frame member15is formed of a molded resin body.

In this surface illumination device13, the point light from the LED1is converted into the linear light by the linear light conversion device2, the linear light obtained by the conversion is diffused in a predetermined direction by the linear light diffusion device9, and the diffused light is radiated on the pair of diffusion plates14A and14B and can be illuminated as the surface light. In this surface illumination device13, the pair of diffusion plates14A and14B are used so that the illumination light can be output from both surfaces. Instead, while one of the diffusion plates remains unchanged, the other one may be replaced with a reflector plate so that the illumination light can be output from one of the surfaces.

The material for the casing of the linear light conversion device2is a material having a high light reflectance such as a reflective material formed of a laminated body of ultrafinely foamed light reflective material and aluminum metal, a reflective material having a reflective layer including polytetrafluoroethylene on a surface, and a reflective material having a reflective layer including barium sulfate on a surface. Thus, not only visible light but also near ultraviolet-light and infrared light can be uniformly reflected. The linear light conversion device2using this casing and an LED emitting near ultraviolet light can be used for a germicidal lamp for water, illumination for curing an adhesive resin, and the like. By incorporating the linear light conversion device2, the surface illumination device13can be used for a backlight of a light emitting liquid crystal display in which a fluorescent material layer is used instead of a color filter layer as well.

EXPLANATION OF REFERENCE NUMERALS

I point light sourceII linear light conversion unitIII linear light diffusion unitIV surface light lighting unita, b light convergence reflector plate1point light source (LED)2,2A,2B linear light conversion unit3,3A to3D casing3oopening4,4A to4C optical reflector plate5center reflection portion6outer reflection portion8linear light diffusion device10fixing plate11linear light diffusion member12through hole13surface illumination device14A,14B diffusion plate15frame member