Abstract:
Provided is an illumination appliance ( 1 ) that illuminates in a direction opposite a direction towards a mounting face (C) thereof, with radiation light of light sources ( 5 ) installed on a main-body housing ( 2 ) mounted on the mounting face (C), wherein the illumination appliance ( 1 ) is equipped with a light-guiding plate ( 11 ) that surrounds the outer circumference of the main-body housing ( 2 ) and protrudes out in the diameter direction thereof, has a light incident face ( 11   a ), and guides light in the diameter direction. Light radiated from the light sources ( 5 ) enters the light-guiding plate ( 11 ) from the light incident face ( 11   a ) thereof, and light radiated from the light-guiding plate ( 11 ) illuminates the mounting face (C).

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to an illumination appliance that is installed on a ceiling surface or the like. 
       BACKGROUND ART  
       [0002]    Patent Document 1 discloses a conventional illumination appliance. This illumination appliance is a ceiling light whose main body housing including a light source provided therein is directly fixed to an installation surface, which is an indoor ceiling surface. The light source is composed of a plurality of LEDs arranged with emission surfaces thereof facing downward. The main body housing is covered on its lower side opposite to the installation surface with a transmissive cover that diffusely transmits therethrough emission light from the light source. The transmissive cover is formed to be so curved that an outer peripheral portion thereof descends with respect to a center portion thereof and to have a peripheral surface that is a cylindrical surface perpendicular to the installation surface. 
         [0003]    Light emitted from the light source, which has become incident on an inner surface of the transmissive cover at a small incidence angle, is diffusely transmitted through the transmissive cover. As a result, uniform illumination light is emitted downward through the transmissive cover, and thus an indoor environment or the like is illuminated. Furthermore, light emitted from the light source, which has become incident on the inner surface of the transmissive cover at a large incidence angle, is reflected off the transmissive cover and then is emitted upward through the peripheral surface of the transmissive cover. 
         [0004]    Illumination appliances of the type directly fixed to an installation surface are configured so that, by illuminating the installation surface to make it bright, they are capable of lessening an impression that a room as a whole is dark. To this end, illumination light is emitted upward through the peripheral surface of the transmissive cover so that the installation surface on which the illumination appliance is installed can be illuminated therewith. 
       LIST OF CITATIONS  
     Patent Literature 
       [0005]    Patent Document 1: JP-A-2010-140797 (pages 5 to 9, FIG. 1) 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0006]    According to the above-described conventional illumination appliance, however, in order to illuminate a wider area of the installation surface, it is required that the transmissive cover be formed to have an increased length in a direction perpendicular to the installation surface. That is, it is required that light emitted to a side opposite to the installation surface be reflected off the transmissive cover to the installation surface side to illuminate the installation surface. This has led to a problem that, while the amount of light reflected off the transmissive cover to be emitted through the peripheral surface is increased, the amount of illumination light in a direction opposite to the installation surface is decreased, which results in a contrary effect that a room as a whole becomes even darker. 
         [0007]    It is an object of the present invention to provide an illumination appliance that is capable of illuminating a wide area of an installation surface without decrease in amount of illumination light in a direction opposite to the installation surface. 
       Solution to the Problem 
       [0008]    In order to achieve the above-described object, the present invention provides an illumination appliance that, by using emission light from a light source provided in a main body housing thereof that is fixed to an installation surface, provides illumination in a direction opposite to the installation surface. The illumination appliance includes a light guide plate that surrounds an outer periphery of the main body housing so as to protrude in a radial direction, has an incidence surface, and guides light. Light emitted from the light source becomes incident on the light guide plate through the incidence surface, and light emitted from the light guide plate is used to illuminate the installation surface. 
         [0009]    According to this configuration, the main body housing is fixed to the installation surface in an indoor environment or the like, and the indoor environment or the like is illuminated with light that is emitted from the light source and travels in the direction opposite to the installation surface. Furthermore, the outer periphery of the main body housing is surrounded by the light guide plate that protrudes in the radial direction, and light emitted from the light source becomes incident on the light guide plate through the incidence surface. The light that has become incident on the light guide plate is guided by the light guide plate and then is emitted, toward the installation surface, from between an inner peripheral side and an outer peripheral side of the light guide plate or from an outer peripheral end of the light guide plate. As a result, the installation surface is illuminated in an area thereof around an area covered by the illumination appliance. 
         [0010]    Furthermore, in the present invention, in the illumination appliance configured as above, the light guide plate is made of a transparent member. 
         [0011]    Furthermore, in the present invention, the illumination appliance configured as above further includes a transmissive cover that covers a side of the main body housing opposite to the installation surface and diffusely transmits therethrough emission light from the light source. Further, the incidence surface is opposed to a peripheral surface of the transmissive cover and is inclined with respect to the installation surface. 
         [0012]    According to this configuration, light that is emitted from the light source and travels in the direction opposite to the installation surface is diffusely transmitted through the transmissive cover and illuminates the indoor environment or the like. Furthermore, part of emission light from the light source is reflected off an inner surface of the transmissive cover and becomes incident on the light guide plate through the inclined incidence surface. 
         [0013]    Furthermore, in the present invention, in the illumination appliance configured as above, the light guide plate has thickness that is larger in the vicinity of the incidence surface than at a position distant from the incidence surface. 
         [0014]    Furthermore, in the present invention, in the illumination appliance configured as above, the light guide plate has a bent portion that is bent from an outer peripheral edge of the light guide plate toward the installation surface. According to this configuration, light guided in the radial direction of the illumination appliance by the light guide plate is bent at the bent portion in a direction to the installation surface and is emitted from the bent portion toward the installation surface. 
         [0015]    Furthermore, in the present invention, in the illumination appliance configured as above, the light guide plate is provided with an annular or dot-shaped concave portion. According to this configuration, light guided by the light guide plate is diffused at the concave portion and is emitted in the direction to the installation surface. 
         [0016]    Furthermore, in the present invention, in the illumination appliance configured as above, the light source emits light having a plurality of wavelengths, and a prism that disperses and emits guided light is provided at a peripheral portion of the light guide plate. According to this configuration, by the prism, light guided by the light guide plate is dispersed in accordance with wavelengths, and thus illumination light having different colors is shone onto the installation surface. 
       Advantageous Effects of the Invention 
       [0017]    According to the present invention, by a light guide plate surrounding an outer periphery of a main body housing, light is guided in a radial direction and used to illuminate an installation surface, and thus a wide area of the installation surface can be illuminated without decrease in amount of illumination light in a direction opposite to the installation surface. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]    [ FIG. 1 ] is a bottom view showing an illumination appliance of a first embodiment of the present invention. 
           [0019]    [ FIG. 2 ] is a top view showing the illumination appliance of the first embodiment of the present invention. 
           [0020]    [ FIG. 3 ] is a front sectional view showing the illumination appliance of the first embodiment of the present invention. 
           [0021]    [ FIG. 4 ] is a detailed view of a region A in  FIG. 3 . 
           [0022]    [ FIG. 5 ] is front sectional view showing a relevant portion of an illumination appliance of a second embodiment of the present invention. 
           [0023]    [ FIG. 6 ] is a front sectional view showing a relevant portion of an illumination appliance of a third embodiment of the present invention. 
           [0024]    [ FIG. 7 ] is a front sectional view showing a relevant portion of an illumination appliance of a fourth embodiment of the present invention. 
           [0025]    [ FIG. 8 ] is a front sectional view showing a relevant portion of an illumination appliance of a fifth embodiment of the present invention. 
           [0026]    [ FIG. 9 ] is a front sectional view showing a relevant portion of an illumination appliance of a sixth embodiment of the present invention. 
           [0027]    [ FIG. 10 ] is a front sectional view showing a relevant portion of an illumination appliance of a seventh embodiment of the present invention. 
           [0028]    [ FIG. 11 ] is a front sectional view showing a relevant portion of an illumination appliance of an eighth embodiment of the present invention. 
           [0029]    [ FIG. 12 ] is a front sectional view showing a light guide plate of an illumination appliance of a ninth embodiment of the present invention. 
           [0030]    [ FIG. 13 ] is a top view showing an illumination appliance of a tenth embodiment of the present invention. 
           [0031]    [ FIG. 14 ] is a front sectional view showing a relevant portion of the illumination appliance of the tenth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0032]    The following describes embodiments of the present invention with reference to the appended drawings.  FIGS. 1 to 3  show a bottom view, a top view, and a side sectional view of an illumination appliance of a first embodiment, respectively. An illumination appliance  1  is formed to be thin and in a circular shape in planar view and includes a main body housing  2  that is directly fixed to an installation surface C such as an indoor ceiling surface. While the following description assumes that the installation surface C is a ceiling surface, the installation surface C may be an indoor side wall or an indoor floor surface. 
         [0033]    The main body housing  2  has an electrical part  3  and a reflection cover  7 . 
         [0034]    The electrical part  3  is arranged at a center portion of the main body housing  2  and formed in a circular shape in planar view, and is covered with an upper cover  3   a  provided on the installation surface C side and with a lower cover  3   b  provided on a side opposite to the installation surface C. Via a fixing portion  3   c  provided on the upper cover  3   a,  the main body housing  2  is fixed to the installation surface C and is connected to a commercial power source. 
         [0035]    In the electrical part  3 , a plurality of substrates (circuit boards)  4  each having a light source  5  such as an LED mounted thereon are arranged in a polygonal shape in planar view. An emission surface of each of the light sources  5  is disposed to be oriented toward a radial direction of the main body housing  2 . Thus, from the light sources  5 , light is radially emitted toward an outer peripheral side of the illumination appliance  1 . 
         [0036]    An optical member  6  that covers the light source  5  is mounted to each of the substrates  4 . The optical member  6  transmits therethrough light from the light source  5  that has become incident thereon from an inner peripheral side thereof, and emits the light to the outer peripheral side thereof. At this time, the optical member  6  refracts the light being transmitted therethrough in a desired direction and causes the light to be reflected off a reflection surface formed on its lower surface or the like. Thus, a desired amount of light is guided to each of the reflection cover  7 , a transmissive cover  8 , and a light guide plate  11 , which will be described later, so that uniform illumination is performed. 
         [0037]    On an outer peripheral side of the upper cover  3   a , the reflection cover  7  of a disk shape is provided. The reflection cover  7  reflects downward emission light from the light sources  5 . Furthermore, an outer peripheral portion of the reflection cover  7  is curved downward (to the side opposite to the installation surface C). 
         [0038]    On an outer peripheral side of the lower cover  3   b , the transmissive cover  8  that is mountable to and demountable from the main body housing  2  is provided. The transmissive cover  8  has a bottom portion  8   a  that is provided so as to be opposed to the reflection cover  7  and a peripheral surface  8   b  (see  FIG. 4 ) that is a cylindrical surface substantially perpendicular to the installation surface C, and diffusely transmits therethrough emission light from the light sources  5 . Furthermore, the bottom portion  8   a  of the transmissive cover  8  is so curved that an outer peripheral portion thereof ascends with respect to a center portion thereof. The illumination appliance  1 , therefore, is formed to be thin at the outer peripheral portion thereof, thus reducing a user&#39;s feeling of being oppressed. 
         [0039]    On the outer peripheral side of the reflection cover  7 , the light guide plate  11  of an annular shape is mounted with a screw  7   a.    FIG. 4  shows a detailed view of a region A in  FIG. 3 . The light guide plate  11  is made of a transparent member of acrylic resin or the like and surrounds an outer periphery of the main body housing  2  so as to protrude in the radial direction. The light guide plate  11  has an incidence portion  11   b,  an extended portion  11   c,  and a bent portion  11   d.    
         [0040]    The incidence portion  11   b  extends in a vertical direction and has an incidence surface  11   a  that faces a center direction of the main body housing  2  and is opposed to the peripheral surface  8   b  of the transmissive cover  8 . The incidence surface  11   a  is formed as an inclined surface that is inclined outward on a lower side thereof with respect to the installation surface C. The extended portion  11   c  extends in the radial direction from a lower end of the incidence portion  11   b  and is so curved as to be convex downward. At an outer peripheral portion of the light guide plate  11 , the bent portion  11   d  is bent from an end portion of the extended portion  11   c  toward the installation surface C and has a curved surface at a tip end thereof. The incidence portion  11   b,  the extended portion  11   c,  and the bent portion  11   d  are formed to be substantially equal in thickness. 
         [0041]    In the illumination appliance  1  configured as above, light emitted from the light sources  5  is guided via the optical members  6  to the reflection cover  7 , the bottom portion  8   a  of the transmissive cover  8 , and the incidence surface  11   a  of the light guide plate  11 . Light that has travelled from the optical members  6  in a direction to the installation surface C is reflected off the reflection cover  7  in a direction to the bottom portion  8   a  of the transmissive cover  8  on a down side of the reflection cover  7 . 
         [0042]    Light that has travelled from the optical members  6  and from the reflection cover  7  in a direction opposite to the installation surface C and become incident on an inner surface of the bottom portion  8   a  of the transmissive cover  8  at an incidence angle smaller than a critical angle is diffusely transmitted through the transmissive cover  8 . As a result, illumination light is emitted downward through the transmissive cover  8 , and thus a down side of the illumination appliance  1  is uniformly illuminated. 
         [0043]    Light that has travelled from the optical members  6  and from the reflection cover  7  in the direction opposite to the installation surface C and become incident on the inner surface of the bottom portion  8   a  of the transmissive cover  8  at an incidence angle larger than the critical angle is reflected off the transmissive cover  8 . The light reflected off the transmissive cover  8  in a direction to the reflection cover  7  is reflected again off the reflection cover  7  and then is emitted as illumination light through the bottom portion  8   a  of the transmissive cover  8 . 
         [0044]    Light (arrow D 1 ) travelling from the optical members  6  in the radial direction of the illumination appliance  1  and light (arrow D 2 ) travelling in the radial direction of the illumination appliance  1  after being reflected off the transmissive cover  8  are transmitted though the peripheral surface  8   b  of the transmissive cover  8 . The light transmitted through the peripheral surface  8   b  of the transmissive cover  8  becomes incident on the light guide plate  11  through the incidence surface  11   a.    
         [0045]    At this time, since the incidence surface  11   a  is inclined, as shown by the arrow D 2 , light reflected off the bottom portion  8   a  of the transmissive cover  8  to be inclined in the direction to the installation surface C becomes incident thereon at a decreased incidence angle. This suppresses reflection of said light off the incidence surface  11   a.  Thus, light guided to a rear side of the reflection cover  7  as a result of being reflected off the incidence surface  11   a  can be decreased to increase light that becomes incident on the incidence surface  11   a,  so that light use efficiency can be improved. 
         [0046]    The light that has become incident on the light guide plate  11  through the incidence surface  11   a  is guided by the light guide plate  11  to an outer peripheral side thereof. Then, as shown by an arrow D 3 , the light is emitted from the tip end of the bent portion  11   d  toward the installation surface C over a predetermined area. As a result, the installation surface C is illuminated in an area thereof around an area covered by the main body housing  2 . 
         [0047]    Furthermore, from between an inner peripheral side and the outer peripheral side of the light guide plate  11 , part of the light being guided by the light guide plate  11  is emitted toward the installation surface C. At this time, with light emitted from the incidence portion  11   b  as shown by an arrow D 4 , the installation surface C is illuminated in an area thereof above the light guide plate  11 . 
         [0048]    As a result, the installation surface C is illuminated in a wide area thereof on an outer side of an area covered by the main body housing  2 , which includes the area thereof above the light guide plate  11 , and thus an impression that a room as a whole is dark can be lessened. Furthermore, from an outer peripheral surface of the bent portion  11   d  bent from the extended portion  11   c,  light is emitted to an outer peripheral side as shown by an arrow D 5 , and thus a wider area on an outer side beyond the light guide plate  11  can be illuminated. 
         [0049]    According to this embodiment, by the light guide plate  11  surrounding the outer periphery of the main body housing  2 , light emitted in the radial direction of the illumination appliance  1 , namely, light emitted from the outer periphery of the main body housing, is guided and used to illuminate the installation surface C. That is, emission light from the peripheral surface  8   b  of the transmissive cover  8  is guided to an outer side of the main body housing  2  and used to illuminate the installation surface C, and thus, unlike the conventional example, it is not required that light emitted to the side opposite to the installation surface C be used to illuminate the installation surface C. Thus, a wide area of the installation surface C can be illuminated without decrease in amount of illumination light in the direction opposite to the installation surface C. 
         [0050]    Furthermore, unlike the conventional example, in order to illuminate a wide area of the installation surface C, it is not required that the peripheral surface  8   b  of the transmissive cover  8  be formed to have an increased length in a direction perpendicular to the installation surface C. That is, the light guide plate  11  is provided to extend in a direction (the radial direction of the main body housing  2 ) parallel to the installation surface C so as to surround the outer periphery of the main body housing  2 , and thus the illumination appliance  1  is not required to have, at the outer peripheral portion thereof, increased thickness in the direction perpendicular to the installation surface C. The illumination appliance  1 , therefore, can be formed to be thin, thus being capable of reducing a user&#39;s feeling of being oppressed. 
         [0051]    Furthermore, since the light guide plate  11  is made of a transparent member, a user can visually recognize that an area of the installation surface C which is covered by the light guide plate  11 , has become bright. This makes the user realize that a wide area of the installation surface C is illuminated, helping create an impression that a room as a whole is bright. 
         [0052]    Furthermore, since the transmissive cover  8  is provided that covers the main body housing  2  on a side thereof opposite to the installation surface C, and the incidence surface  11   a  is inclined with respect to the installation surface C, light that is reflected off the bottom portion  8   a  of the transmissive cover  8  to become incident on the incidence surface  11   a  can be made incident thereon at a decreased incidence angle. Thus, reflection light reflected off the incidence surface  11   a  is decreased, so that light use efficiency can be improved. 
         [0053]    In this case, more preferably, the incidence surface  11   a  is so formed that a lower end thereof is disposed immediately below a boundary B on the installation surface C side between the incidence portion  11   b  and the extended portion  11   c.  With this configuration, when the illumination appliance  1  is seen from below, the boundary B and a ridge line of the lower end of the incidence surface  11   a  coincide with each other, and thus an aesthetic impression with reduced occurrence of stripes can be achieved. 
         [0054]    Furthermore, since the light guide plate  11  has the bent portion  11   d  bent from an outer peripheral edge thereof toward the installation surface C, the installation surface C is illuminated with light emitted from the tip end of the bent portion  11   d  as shown by the arrow D 3 , and from the outer peripheral surface of the bent portion  11   d  that is bent, light is emitted to the outer peripheral side as shown by the arrow D 5 . With this configuration, guided light can be emitted in separate directions that are toward above the light guide plate  11  and toward the outer side beyond the light guide plate  11 , respectively. This allows a wider area of the installation surface C to be illuminated. 
         [0055]    Furthermore, with light emitted from the incidence portion  11   b  as shown by the arrow D 4 , the installation surface C is illuminated in the area thereof above the light guide plate  11 , and light is emitted from the bent portion  11   d  as shown by the arrows D 3  and D 5  also to the area of the installation surface C on an outer side of the area covered by the light guide plate  11 . With this configuration, a wide area of the installation surface C can be illuminated in such a manner that illuminance at the installation surface C gradually decreases with increasing distance from an outer periphery of the illumination appliance  1 , and there can be obtained an illumination state where variation in illuminance level at the installation surface C are unlikely to be perceived, and thus user discomfort is reduced. 
         [0056]    Next,  FIG. 5  is a front sectional view showing a relevant portion of an illumination appliance of a second embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing first embodiment shown in  FIGS. 1 to 4  are denoted by the same reference symbols. In this embodiment, a light guide plate  12  shaped differently from the light guide plate  11  of the first embodiment is provided. Parts other than that are the same as those in the first embodiment. 
         [0057]    Similarly to the foregoing light guide plate  11  shown in  FIG. 4 , the light guide plate  12  is made of a transparent member of acrylic resin or the like and has an incidence portion  12   b,  an extended portion  12   c,  and a bent portion  12   d . An incidence surface  12   a  of the incidence portion  12   b  faces the center direction of the main body housing  2 , is opposed to the peripheral surface  8   b  of the transmissive cover  8 , and is formed to be substantially perpendicular to the installation surface C. The extended portion  12   c  extends in the radial direction from a lower end of the incidence portion  12   b  and is so curved as to be convex downward. At an outer peripheral portion of the light guide plate  12 , the bent portion  12   d  is bent from an end portion of the extended portion  12   c  toward the installation surface C. The incidence portion  12   b,  the extended portion  12   c,  and the bent portion  12   d  are formed to be substantially equal in thickness. 
         [0058]    According to this embodiment, similar effect to that provided by the first embodiment can be obtained. In this case, since the incidence surface  12   a  is formed to be substantially perpendicular to the installation surface C, a larger amount of light than in the first embodiment is reflected off the incidence surface  12   a  in the direction to the installation surface C. In a case, however, where the peripheral surface  8   b  has a reduced length and the illumination appliance  1  thus is formed to be thin, light that becomes incident on the incidence surface  12   a , in a state of being inclined in the direction to the installation surface C, is decreased, and thus decrease in light use efficiency can be suppressed. 
         [0059]    Furthermore, light travelling from the optical members  6  in the radial direction of the illumination appliance  1  without being reflected off the bottom portion  8   a,  which is shown by the arrow D 1  (see  FIG. 4 ), becomes incident on the incidence surface  12   a  substantially perpendicularly thereto. With this configuration, incidence light that becomes incident on the incidence surface  12   a  can be made incident thereon at a decreased incidence angle, and thus light reflected off the incidence surface  12   a  can be decreased to increase light that becomes incident on the incidence surface  12   a.    
         [0060]    Next,  FIG. 6  is a front sectional view showing a relevant portion of an illumination appliance of a third embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing second embodiment shown in  FIG. 5  are denoted by the same reference symbols. In this embodiment, a light guide plate  13  shaped differently from the light guide plate  12  of the second embodiment is provided. Parts other than that are the same as those in the second embodiment. 
         [0061]    Similarly to the foregoing light guide plate  12  shown in  FIG. 5 , the light guide plate  13  is made of a transparent member of acrylic resin or the like and has an incidence portion  13   b , an extended portion  13   c,  and a bent portion  13   d.  An incidence surface  13   a  of the incidence portion  13   b  faces the center direction of the main body housing  2 , is opposed to the peripheral surface  8   b  of the transmissive cover  8 , and is formed to be substantially perpendicular to the installation surface C. The extended portion  13   c  extends in the radial direction from a lower end of the incidence portion  13   b  and is so curved as to be convex downward. At an outer peripheral portion of the light guide plate  13 , the bent portion  13   d  is bent from an end portion of the extended portion  13   c  toward the installation surface C. 
         [0062]    The extended portion  13   c  and the bent portion  13   d  are formed to be substantially equal in thickness. Furthermore, the incidence portion  13   b  of the light guide plate  13  is formed to have thickness that is larger in the vicinity of the incidence surface  13   a  than at a position distant from the incidence surface  13   a.  That is, the incidence portion  13   b  is formed so that light that has become incident through the incidence surface  13   a  becomes incident on a surface of the incidence portion  13   b  on the installation surface C side at an angle not less than the critical angle (on the order of about 45 degrees). With this configuration, light emitted from the incidence portion  13   b  as shown by an arrow D 4  is decreased, and light that becomes incident through the incidence surface  13   a  and is guided is increased. Thus, in addition to obtaining similar effect to that provided by the second embodiment, it is possible to illuminate an outer side of the light guide plate  13  with increased brightness. 
         [0063]    In this case, since a lower end of the incidence surface  13   a  does not coincide with a boundary B on the installation surface C side between the incidence portion  11   b  and the extended portion  11   c,  and thus when the illumination appliance  1  is seen from below, an aesthetic impression with increased occurrence of stripes can be achieved. 
         [0064]    Next,  FIG. 7  is a front sectional view showing a relevant portion of an illumination appliance of a fourth embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing third embodiment shown in  FIG. 6  are denoted by the same reference symbols. In this embodiment, a light guide plate  13  configured similarly to that in the third embodiment is provided with a concave portion  13   e.  Parts other than that are the same as those in the third embodiment. 
         [0065]    On an installation surface C side of the light guide plate  13 , the concave portion  13   e  is formed to be annularly concave, and a plurality of the concave portions  13   e  are concentrically provided. Part of light guided by the light guide plate  13  is diffusely emitted to the installation surface C side via the concave portions  13   e  as shown by an arrow D 6 . Thus, in addition to obtaining similar effect to that provided by the third embodiment, it is possible to uniformly illuminate the installation surface C in an area thereof above the light guide plate  13 . In this case, when the illumination appliance  1  is seen from below, stripes attributable to the concave portions  13   e  are visually recognized, and thus an aesthetic impression with increased occurrence of stripes can be achieved. 
         [0066]    A multitude of annular concave portions  13   e  may be provided, or alternatively, a multitude of dot-shaped concave portions  13   e  may be formed. By appropriately changing the shape and number of concave portions  13   e  used, the installation surface C can be more uniformly illuminated. Furthermore, a concave portion configured similarly to the concave portion  13   e  may be provided also in the other embodiments. 
         [0067]    Next,  FIG. 8  is a front sectional view showing a relevant portion of an illumination appliance of a fifth embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing third embodiment shown in  FIG. 6  are denoted by the same reference symbols. In this embodiment, a light guide plate  14  shaped differently from the light guide plate  13  of the third embodiment is provided. Parts other than that are the same as those in the third embodiment. 
         [0068]    Similarly to the foregoing light guide plate  13  shown in  FIG. 6 , the light guide plate  14  is made of a transparent member of acrylic resin or the like and has an incidence portion  14   b,  an extended portion  14   c,  and a bent portion  14   d.  An incidence surface  14   a  of the incidence portion  14   b  faces the center direction of the main body housing  2 , is opposed to the peripheral surface  8   b  of the transmissive cover  8 , and is formed to be substantially perpendicular to the installation surface C. The extended portion  14   c  extends in the radial direction from a lower end of the incidence portion  14   b  and is so curved as to be convex downward. Furthermore, the extended portion  14   c  is so inclined as to descend on an outer peripheral side thereof 
         [0069]    At an outer peripheral portion of the light guide plate  14 , the bent portion  14   d  is bent from an end portion of the extended portion  14   c  toward the installation surface C. In this case, the bent portion  14   d  is inclined with respect to the installation surface C. Furthermore, the incidence portion  14   b,  the extended portion  14   c,  and the bent portion  14   d  are formed to be substantially equal in thickness. 
         [0070]    According to this embodiment, similar effect to that provided by the third embodiment can be obtained. Furthermore, since the extended portion  14   c  of the light guide plate  14  is so inclined as to descend on the outer peripheral side thereof, the bent portion  14   d  is disposed at a position lower in level compared with the bent portion  13   d  (see  FIG. 6 ) of the third embodiment. Thus, light emitted from an outer peripheral surface of the bent portion  14   d  as shown by the arrow D 5  is emitted from a position lower in level, so that a wider area of the installation surface C can be illuminated. 
         [0071]    Next,  FIG. 9  is a front sectional view showing a relevant portion of an illumination appliance of a sixth embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing fifth embodiment shown in  FIG. 8  are denoted by the same reference symbols. In this embodiment, a light guide plate  15  shaped differently from the light guide plate  14  of the fifth embodiment is provided. Parts other than that are the same as those in the fifth embodiment. 
         [0072]    Similarly to the foregoing light guide plate  14  shown in  FIG. 8 , the light guide plate  15  is made of a transparent member of acrylic resin or the like and has an incidence portion  15   b,  an extended portion  15   c,  and a bent portion  15   d.  An incidence surface  15   a  of the incidence portion  15   b  faces the center direction of the main body housing  2 , is opposed to the peripheral surface  8   b  of the transmissive cover  8 , and is formed to be substantially perpendicular to the installation surface C. The extended portion  15   c  extends in the radial direction from a lower end of the incidence portion  15   b  and is so curved as to be convex downward. Furthermore, the extended portion  15   c  is so inclined as to descend on an outer peripheral side thereof. 
         [0073]    At an outer peripheral portion of the light guide plate  15 , the bent portion  15   d  is bent from an end portion of the extended portion  15   c  toward the installation surface C. In this case, the bent portion  15   d  is formed to be substantially perpendicular to the installation surface C. Furthermore, the incidence portion  15   b , the extended portion  15   c,  and the bent portion  15   d  are formed to be substantially equal in thickness. 
         [0074]    According to this embodiment, similar effect to that provided by the fifth embodiment can be obtained. Furthermore, the bent portion  15   d  of the light guide plate  15  is formed to be substantially perpendicular to the installation surface and thus has a larger bending angle with respect to the extended portion  15   c  compared with that of the bent portion  14   d  (see  FIG. 8 ) of the fifth embodiment. Because of this, light guided by the light guide plate  15  to reach an outer peripheral surface of the bent portion  15   d  as shown by an arrow D 7  becomes incident on the outer peripheral surface at an increased incidence angle. With this configuration, the amount of light emitted from the outer peripheral surface of the bent portion  15   d  as shown by the arrow D 5  is increased, and thus an outer side of the light guide plate  15  can be made brighter. 
         [0075]    Next,  FIG. 10  is a front sectional view showing a relevant portion of an illumination appliance of a seventh embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing first embodiment shown in  FIGS. 1 to 4  are denoted by the same reference symbols. In this embodiment, a light guide plate  16  shaped differently from the light guide plate  11  of the first embodiment is provided. Parts other than that are the same as those in the first embodiment. 
         [0076]    Similarly to the foregoing light guide plate  11  shown in  FIG. 4 , the light guide plate  16  is made of a transparent member of acrylic resin or the like and has an incidence portion  16   b  and an extended portion  16   c . An incidence surface  16   a  of the incidence portion  16   b  faces the center direction of the main body housing  2 , is opposed to the peripheral surface  8   b  of the transmissive cover  8 , and is formed to be substantially perpendicular to the installation surface C. Furthermore, similarly to the third embodiment (see  FIG. 6 ), the incidence portion  16   b  is formed to have thickness that is larger in the vicinity of the incidence surface  16   a  than at a position distant from the incidence surface  16   a.    
         [0077]    The extended portion  16   c  extends substantially horizontally in the radial direction from a lower end of the incidence portion  16   b . With this configuration, light is emitted from a tip end of the extended portion  16   c  as shown by the arrow D 3  and illuminates the installation surface C. Here, no counterpart of the bent portion  11   d  (see  FIG. 4 ) bent from an end portion of the extended portion  16   c  is not provided. 
         [0078]    According to this embodiment, similarly to the first embodiment, light is guided in the radial direction by the light guide plate  16  surrounding the outer periphery of the main body housing  2  and used to illuminate the installation surface C. Thus, by guiding emission light from the peripheral surface  8   b  of the transmissive cover  8  to the outer side of the main body housing  2 , a wide area of the installation surface C can be illuminated without decrease in amount of illumination light in the direction opposite to the installation surface C. 
         [0079]    Furthermore, similarly to the third embodiment, light emitted from the incidence portion  16   b  as shown by the arrow D 4  is decreased, and light that becomes incident through the incidence surface  16   a  and is guided is increased. Thus, an outer side of the light guide plate  16  can be illuminated with increased brightness. 
         [0080]    Next,  FIG. 11  is a front sectional view showing a relevant portion of an illumination appliance of an eighth embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing seventh embodiment shown in  FIG. 10  are denoted by the same reference symbols. In this embodiment, a light guide plate  16  configured similarly to that in the seventh embodiment is provided with a concave portion  16   e . Parts other than that are the same as those in the seventh embodiment. 
         [0081]    On a side of the light guide plate  16  opposite to the installation surface C, the concave portion  16   e  is formed to be annularly concave, and a plurality of the concave portions  16   e  are concentrically provided. Part of light guided by the light guide plate  16  is diffusely emitted to the installation surface C side via the concave portions  16   e  as shown by the arrow D 6 . Thus, in addition to obtaining similar effect to that provided by the seventh embodiment, it is possible to uniformly illuminate the installation surface C in an area thereof above the light guide plate  16 . In this case, when the illumination appliance  1  is seen from below, stripes attributable to the concave portions  16   e  are visually recognized, and thus an aesthetic impression with increased occurrence of stripes can be achieved. 
         [0082]    A multitude of annular concave portions  16   e  may be provided, or alternatively, a multitude of dot-shaped concave portions  16   e  may be formed. By appropriately changing the shape and number of the concave portions  16   e  used, the installation surface C can be more uniformly illuminated. Furthermore, a concave portion configured similarly to the concave portion  16   e  may be provided also in the other embodiments. 
         [0083]    Next, description is given of a ninth embodiment. In this embodiment, a light guide plate  11  configured similarly to and having the same shape as that in the foregoing first embodiment shown in  FIGS. 1 to 4  is partly processed for non-glare surface treatment. Parts other than that are the same as those in the first embodiment. 
         [0084]      FIG. 12  is a front sectional view of the light guide plate  11  of this embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing first embodiment shown in  FIGS. 1 to 4  are denoted by the same reference symbols. Through surface texturing or the like, non-glare surface treatments  11   e  and  11   f  are applied to tip ends of an incidence surface  11   a  and a bent portion  11   d  of the light guide plate  11 , respectively. 
         [0085]    By the non-glare surface treatment  11   e,  light that becomes incident on the light guide plate  11  through the incidence surface  11   a  is diffused. Thus, light emitted from an incidence portion  11   b  as shown by the arrow D 4  is diffused. Furthermore, by the non-glare surface treatment  11   f,  light emitted from the tip end of the bent portion  11   d  is diffused. This reduces variation in illuminance level at the installation surface C (see  FIG. 4 ) in an area thereof above the light guide plate  11  and thus can prevent stripes attributable to the shape of the light guide plate  11  from occurring on the installation surface C. 
         [0086]    Next,  FIGS. 13 and 14  are a top view and a front sectional view, respectively, showing an illumination appliance of a tenth embodiment. For the sake of convenience in explanation, like parts corresponding to those in the foregoing first embodiment shown in  FIGS. 1 to 4  are denoted by the same reference symbols. In this embodiment, a main body housing  2  is formed in a substantially rectangular shape in planar view, and the transmissive cover  8  (see  FIG. 3 ) is not provided. Furthermore, a light guide plate  17  shaped differently from the light guide plate  11  of the first embodiment is provided. Parts other than these are the same as those in the first embodiment. 
         [0087]    An electrical part  3  of the main body housing  2  is arranged at a center portion of the main body housing  2  and formed in a rectangular shape in planar view. In the electrical part  3 , a plurality of substrates  4  each having a light source  5  such as an LED mounted thereon are arranged in a polygonal shape in planar view. A reflection cover  7  is formed in a substantially rectangular shape in planar view and is provided on an outer peripheral side of the electrical part  3  on the installation surface C side. 
         [0088]    An optical member  6  that covers the light source  5  is mounted to each of the substrates  4 . The optical member  6  transmits therethrough light from the light source  5  that has become incident thereon from an inner peripheral side thereof, and emits the light to an outer peripheral side thereof At this time, the optical member  6  refracts the light being transmitted therethrough in a desired direction and causes the light to be reflected off a plurality of reflection surfaces  6   a  and  6   b.    
         [0089]    Similarly to the foregoing light guide plate  11  shown in  FIG. 4 , the light guide plate  17  is made of a transparent member of acrylic resin or the like and has an incidence portion  17   b  and an extended portion  17   c . An incidence surface  17   a  of the incidence portion  17   b  is formed to face a center direction of the main body housing  2 . The extended portion  17   c  extends in a radial direction from a lower end of the incidence portion  17   b  and is so curved as to be convex downward. 
         [0090]    At an outer peripheral portion of the light guide plate  17 , a prism  17   f  having a substantially triangular sectional shape is provided so as to be continuous with the extended portion  17   c  and to protrude downward. The incidence portion  17   b  and the extended portion  17   c  are formed to be substantially equal in thickness. Here, no counterpart of the bent portion  11   d  (see  FIG. 4 ) bent from an end portion of the extended portion  17   c  in the direction to the installation surface C is not provided. 
         [0091]    In the illumination appliance  1  configured as above, light emitted from the light sources  5  is transmitted through the optical members  6 . With light guided from the optical members  6  to the side opposite to the installation surface C as shown by arrows E 1  and E 2 , the down side of the illumination appliance  1  is illuminated. Furthermore, light guided from the optical members  6  to the reflection cover  7  as shown by arrows E 3 , E 4 , and E 5  is reflected off the reflection cover  7  and illuminates the down side. Light that has reached a lower surface of the light guide plate  17  from the optical members  6  as shown by an arrow E 6  is reflected off the light guide plate  17  and illuminated the down side. 
         [0092]    Light (arrow D 1 ) travelling from the optical members  6  in the radial direction of the illumination appliance  1  becomes incident on the light guide plate  17  through the incidence surface  17   a.  As shown by the arrow D 3 , light guided by the light guide plate  17  is emitted via the extended portion  17   c  toward the installation surface C over a predetermined area. As a result, the installation surface C is illuminated in an area thereof around an area covered by the main body housing  2 . Furthermore, with light emitted from the incidence portion  17   b  as shown by the arrow D 4 , the installation surface C is illuminated in an area thereof above the light guide plate  17 . 
         [0093]    Furthermore, as shown by an arrow D 8 , light guided from the optical members  6  to the prism  17   f  of the light guide plate  17  is refracted while being transmitted through the prism  17   f  and then is emitted therefrom. As a result, the installation surface C is illuminated in an area thereof on an outer side of an area covered by the light guide plate  17 . At this time, in a case where light having a plurality of wavelengths is emitted from the light sources  5 , emission light from the prism  17   f  is dispersed in accordance with the wavelengths. Thus, illumination light having different colors is shone onto the installation surface C, so that a color-coded pattern such as a rainbow pattern can be formed thereon. 
         [0094]    According to this embodiment, similarly to the first embodiment, light is guided in the radial direction by the light guide plate  17  surrounding the outer periphery of the main body housing  2  and used to illuminate the installation surface C. Thus, by guiding light that has reached the incidence surface  17   a  from the light sources  5  to the outer side of the main body housing  2 , a wide area of the installation surface C can be illuminated without decrease in amount of illumination light in the direction opposite to the installation surface C. 
         [0095]    Furthermore, since the prism  17   f  is provided at a tip end of the light guide plate  17 , a color-coded pattern such as a rainbow pattern can be formed on the installation surface C. The light guide plates of the other embodiments also may be provided with a similarly configured prism. 
         [0096]    In the first to tenth embodiments, the light guide plates  11  to  17  may be formed to be divided in a circumferential direction, as long as they extend in the circumferential direction so as to surround the outer peripheral portion of the main body housing  2 . Furthermore, any of the light guide plates  11  to  17  may be formed integrally with the reflection cover  7  by double molding or the like. 
       INDUSTRIAL APPLICABILITY  
       [0097]    The present invention is applicable to illumination appliances that are installed on a ceiling surface or the like. 
       LIST OF REFERENCE SYMBOLS  
       [0098]      1  illumination appliance 
         [0099]      2  main body housing 
         [0100]      3  electrical part 
         [0101]      4  substrate 
         [0102]      5  light source 
         [0103]      6  optical member 
         [0104]      7  reflection cover 
         [0105]      8  transmissive cover 
         [0106]      11  to  17  light guide plate 
         [0107]      11   a  to  17   a  incidence surface 
         [0108]      11   b  to  17   b  incidence portion 
         [0109]      11   c  to  17   c  extended portion 
         [0110]      11   d  to  15   d  bent portion 
         [0111]      13   e,    16   e  concave portion 
         [0112]      17   f  prism