Abstract:
There is provided a light emitting device in this invention comprises a light source for supplying light, and plural light scattering devices disposed in front of the light source so as to be opposite to the direction of the light. Each of the light scattering devices comprises at least one striated surface forming plural prisms. The light is scattered by means of the prisms of the light scattering devices. 
     This invention enables a light emitting device to achieve the spread of light with comparatively little light clustering. In particular, the light emitted from a local source can be changed from being directional to being non-directional even in case of use of the LED&#39;s source of light which is directional and so on. Therefore, the light emitting device pertaining to this invention is suitably adopted for use in the display of guardrails on the road. Moreover, in the case of using LED elements as the source of light, since LED&#39;s have a long lifetime and low power consumption, the device can be provided using a solar battery as a power source, thereby eliminating the trouble of battery replacement. Moreover, the adoption of the LED makes it easy to obtain the required power from a battery, and to eliminate defects such as broken wires caused by vehicular traffic, because conventional electric wires for supplying power are not required. Therefore, for example, the light emitting device with regard to this invention is suitable for use as an alarm light at construction sites.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a light emitting device. 
     2. Relevant Art 
     There are known technologies for dispersing and spreading light from a light source. For instance, Japanese Patent Laid-open Publication No. (Tokkai-Hei) 11-176220 discloses a technology which obtains the spread of light by reflecting the light and further dispersing the light two times. This technology has, however, a problem in that the amount of light is reduced because the light is reflected and the structure is apt to become complicated and large-sized. 
     Aside therefrom, Japanese Utility ModelLaid-open Publication No. (Jikkai-Hei) 5-15209 discloses the technology for achieving the spread of light by stacking a milky-white board and prism film. This technology has, however, a disadvantage in that the effect of scattering is insufficient, and therefore, the source of light can be seen as a dot shape in case of use of a point source of light such as LED element. 
     Therefore, the inventor has experimented in various ways and observed that he obtained the spread of light even in case of use of a point light source by stacking two or more scattering sheets (two sheets, for example) with striated surfaces forming plural prisms. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a light emitting device capable of achieving the spread of a light source with comparatively little clustering even in the case of use of a local source of light such as a point light source or a linear light source. A light emitting device in this invention comprises a light source for supplying light, and plural light scattering devices disposed in front of the light source so as to be opposite to the direction of the light. Each of the light scattering devices comprises at least one striated surface forming plural prisms. The light is scattered by means of the prisms of the light scattering devices. 
     This invention enables a light emitting device to achieve the spread of light with comparatively little light clustering. In particular, the light emitted from a local source can be changed from being directional to being non-directional even in case of use of the LED&#39;s source of light which is directional and so on (not limited to this type of light source). Therefore, the light emitting device pertaining to this invention is suitably adopted for use in the display of guardrails on the road. Moreover, in the case of using LED elements as the source of light, since LED&#39;s have a long lifetime and low power consumption, the device can be provided using a solar battery as a power source, thereby eliminating the trouble of battery replacement. Moreover, the adoption of the LED which emits light using little power makes it easy to obtain the required power from a battery, and to eliminate defects such as broken wires caused by vehicular traffic, because conventional electric wires for supplying power are not required. Therefore, for example, the light emitting device with regard to this invention is suitable for use as an alarm light at construction sites. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross section of the light emitting device according to the first embodiment of this invention. 
     FIG. 2 is a front view of the light emitting device of FIG.  1 . 
     FIG.  3 ( a ) is a front view of the first light scattering plate used in the first embodiment. 
     FIG.  3 ( b ) is a cross sectional view of a part of the first light scattering plate used in the first embodiment. 
     FIG. 4 is a side cross section of the light emitting device according to the second embodiment of this invention. 
     FIG. 5 is a front view of the light emitting device in FIG.  4 . 
     FIG. 6 is a side cross section of the light emitting device according to the third embodiment. 
     FIG. 7 is a explanatory drawing for the fourth embodiment of this Invention, which refers to the light emitting device including the first and second light scattering plate  60  and  70  and the transparent plate  80  surrounding the main plate  20 , cut along the axial direction thereof. 
     FIG. 8 is an explanatory drawing with the part referred to by the sign A in FIG. 7 enlarged. 
     FIG. 9 is a plain view of the light emitting device according to the fourth embodiment of this invention. 
     FIG. 10 is a plan view of the light emitting device according to the fifth embodiment of this invention. 
     FIG. 11 is a front view of the light emitting device pertaining to the sixth embodiment of this Invention. 
     FIG. 12 is a schematic enlarged cross sectional view of a substantial part of the light emitting device pertaining to the seventh embodiment of this invention. 
     FIG. 13 is an explanatory drawing to explain the arrangement of the electrodes in FIG. 12 as a plan view. 
     FIG. 14 is an explanatory enlarged drawing of part B shown in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The light emitting device of the first embodiment of this invention is explained in detail based on FIGS. 1 to  3 . 
     FIG. 1 is a cross section where the light emitting device is seen from the side thereof. The light emitting device has a main cover  1  with a bowl-like shape opened at one side. A disc shaped main plate (main body)  2  is installed inside the main cover  1 . Two or more LED elements  3  are densely set on one side of the main plate  2 . A battery control box (power unit)  4  is laid at the other side of main plate  2  to blink the LED elements  3 . The battery control box  4  can be freely operated by switch  5  exposed on the outside of the main cover  1  and it is designed to provide LED elements  3  from the battery control box  4  with power by way of the switch  5 . 
     A first light scattering plate  6  (corresponding to the light scattering device) is installed to conceal the opening of the main cover  1 , situated in front of the plural LED elements  3  equipped on the main plate  2 . The light scattering plate  6  has a thin discoid shape, and one side thereof has striated concentric wavy circles forming plural prisms thereon. A second convex light scattering plate  7  (corresponding to the light scattering device) is set in the opening of the main cover  1  placed further outside of the first scattering plate  6 . Concentric wavy circles are made on one side of the second light scattering plate  7  in a manner similar to those on the first light scattering plate  6 . The second light scattering plate  7  is fixed to the marginal rib of the opening of the main cover  1  through a suppression ring  8  and a fastening screw  9 . Symbol  10  shown in the figures denotes an O-ring. 
     FIG.  2  and FIG. 3 show front views of the light scattering plates  6  and  7  respectively. Light scattering plates  6  and  7  are semi-transparent, and the striated ridge lines on the reverse side can be seen through in FIG.  2  and FIG.  3 . As shown in FIG.  3 ( b ), the cross-sectional shape of the striated surface is triangular, and plural slopes are formed inclined against the surface on the side of the light scattering plate  6 . The form of striation of the surface should not be limited. The striations can also be formed on the opposite side of the light scattering plates  6  and  7 , either alternatively or additionally. The striated surface formed in the light scattering plate  7  has a similar shape to that shown in FIG.  3 ( b ). 
     The light scattering plates  6  and  7  are made from a resin which is suitably selected from well-known resins such as polycarbonates, acrylics, and polypropylenes, etc. In addition, dispersion materials by which light is scattered are mixed into the light scattering plates  6  and  7 . Dispersion materials are suitably selected from among those which are well-known. For instance, the mixture of a glass powder with a diameter of 0.5 micrometer and clay can be used as the dispersion material in this embodiment. In this embodiment, the light scattering boards  6  and  7  are made as milky-white half transparent boards. The light scattering plate can be made a colored semi transparency by mixing the resin with pigment, without limiting to a milky-white color. In this case, a preferable color can be obtained. It can be used, for instance, for the signal lights. Light emitted from LED  3  is scattered by two or more concentric circle striations formed on the back of the light scattered board  6  and  7 , functioning as a prism. Such light scattering plates  6  and  7  themselves can be those which are already known. 
     It was observed by the inventor that a single use of a light scattering plate placed in front of an LED light source allowed the point light source of each LED to be seen clearly, through experimentation. On the other hand, the arrangement of two sheets of light scattering plates gave the satisfactory result of spreading the light over the surface because point light sources are difficult to discern as light emitted from separate LED light sources. 
     FIGS.  4  and FIG. 5 have the same reference symbol attached to the same material, and show the light emitting device pertaining to the second embodiment of this invention. Suppression ring  8  which sets the second light scattering plate  7  in the main cover  1  is elongated radially compared to the aforementioned first embodiment. On an elongated portion of the suppression ring  8 , two or more concavities are formed, spaced in the circumferential direction. Solar panels (solar cells)  11  are set in the two or more concavities. Cover  12  covers the front side of solar panel  11 . It is possible to emit light using LED&#39;s at a lower cost over a long period by charging the battery with the solar panel  11 . 
     FIG. 6 has the same reference symbol attached to the same material and shows the light emitting device pertaining to the third embodiment of this invention. As seen in FIG. 6, LED elements  3  are disposed on both the right side and left side. This embodiment is suitably adapted to guard rails on the road facing traffic. As for the main cover  1 , both ends are made to be opened in a short cylindrical shape. Battery control box  4  is installed in the main cover  1 . Two main plates  2  are set in an orthogonal direction with respect to the axis of the main cover  1  with the battery control box  4  in between. Two or more LED elements  3  are installed on the surface of the main plate  2 . Two first light scattering plates  6  are installed to conceal the openings of both the right and left ends of main cover  1 . The second light scattering plates  7  are installed further outside of the first light scattering plates  6  respectively as seen in FIG.  6 . Both first and second light scattering plates extend in an orthogonal direction with respect to the axis of main cover  1 . However, concerning the second scattering plate  7 , the top thereof is positioned orthogonally with respect to the axis of main cover  1 . Moreover, it is possible for the LED elements to be composed of a mixture of LED elements  3  emitting red and blue light. When LED elements  3  with red and blue light which emit the light separately by switch are provided, it can be used as a red and blue signal light. 
     FIGS. 7 to  9  show the light emitting device pertaining to the fourth embodiment of the invention. This embodiment has a cylindrical main plate (hereinafter, the word “plate” includes a cylindrical shape)  20  in place of the main plate  2  described above. Four rows of LED elements  31 - 34  are installed, as shown in FIG.  7  and FIG. 9, on the outside surface of the main plate  20 . LED elements  31 - 34  are spaced along the direction of the axis in each row and at 90 degrees with respect to the circumferential direction. Each row of LED elements  31 - 34  is set to obtain a different color of luminescence in this embodiment. For example, row of LED elements  31  can be set to red, row of LED elements  32  to blue, row of LED elements  33  to green and row of LED elements  34  to orange. The luminescence color, which can be any color besides the abovementioned combinations such as white, can be selected at the discretion. of the user. That is, the colors of the sources of light are different along the circumferential direction of the main plate  20 . As an alternative, LED element(s) with plural luminescence colors from one element can also be used. In this case, the luminescence color of the LED element can be randomly controlled with a control device (not shown in the drawing). Main plate  20  can be rotated in either a clockwise or counterclockwise direction by control motor  101  through shaft  103  and gear  102 . The bearing supports the shaft  103 . The control motor  101  is designed to rotate the main plate  20  at an arbitrary speed and angle. 
     The first light scattering plate  60  (refer to FIG. 8) is arranged on the outside of main plate  20 . The basic structure of the first light scattering plate  60  is similar to that of the said first light scattering plate  6 . However, the striations do not extend in concentric circles but in a mutually parallel direction (the horizontal direction in FIG. 7) in this embodiment. Moreover, the first light scattering plate  60  is, as a whole, formed in a cylindrical shape which is concentric with main plate  20 . 
     The transparent plate  80  having a cylindrical shape and concentric with the first light scattering plate  60  is placed on the outside thereof. Transparent plate  80  is made from transparent materials (for instance, acrylic board) with a hightransmissivity. 
     The second light scattering plate  70  having cylindrical shape and concentric with the transparent plate  80  is placed on the outside thereof. The structure of the second light scattering plate  70  is almost the same as that of the first light scattering plate  60 . However, the inclination of the striations of the second light scattering plate  70  and those of the first light scattering plate  60  are oriented in mutually inverse directions. In other words, the shape of the striations formed on the surface of the first light scattering plate are the inverse of those formed on the surface of the second light scattering plate. This results in improving the effect of light scattering. 
     The explanation concerning the other structures are omitted for being similar to those of the first embodiment. 
     Next, the operation of the light emitting device pertaining to this embodiment is explained here. In this embodiment, the arrangement of the first and second light scattering plate  60  and  70  achieve a satisfactory result of spreading the light on the surface because points of light are difficult to discern in the case of using separate light distribution emitted from individual LED elements  31  to  34 . 
     Moreover, the distance from the inside diameter of the first scattering plate  60  to the outside diameter of the second scattering plate  70  is set to about 2 mm in this embodiment. However, the provision of the transparent board  80  between the first scattering plate  60  and second scattering plate  70 , to separate the plate  60  from the plate  70 , leads to the good effect of light scattering and spreading with better quality although the first and the second scattering plate  60  and  70  are thin. 
     In addition, in this embodiment, since the color of each of the LED element  31 - 34  is made different, a device can be obtained which emits an arbitrary color by means of turning the LED elements having the preferred color to the front or to the desired direction. 
     Next, the light emitting device pertaining to the fifth embodiment of this invention is explained in accordance with FIG.  10 . In this embodiment, the first and the second light scattering plates  160  and  170 , and the transparent plate wedged between them is placed at the outside of the second light scattering plate  170 . The structure of the first and the second light scattering plates  160  and  170 , and the transparent board wedged between them is similar to that of the fourth embodiment except for the diameter thereof. Moreover, eight rows of LED elements  131 - 138  are installed in this embodiment. The detailed explanation is omitted because the structure other than these is substantially the same as the fourth embodiment described the above. 
     According to the light emitting device of the fifth embodiment, it is possible to obtain the spread of light with a stronger effect of light scattering than that of the fourth embodiment. Moreover, the structure in the fifth embodiment can obtain strong effects of light scattering in spite of the fact that the first and the second light scattering plates and the transparent board are considerably thin. This has resulted in obtaining a spread of light with still better quality because both of a sufficient amount of light and a strong scattering effect can be obtained. Experiments showed that the lower the height and the smaller the pitch, the more effective the scattering is in the striated prisms in the first and the second light scattering plates. 
     Next, the light emitting device pertaining to the sixth embodiment of this invention will be explained in accordance with FIG. 11. A transparent outer cylinder  200  covering the outside of the second light scattering plate  170  is equipped in this embodiment. Moreover, a base  300  storing a motor  101  is equipped and two or more suction cups  301  are attached under it. In addition, in this embodiment, the motor  101  directly drives the shaft  103 . 
     According to the light emitting device of the sixth embodiment, the suction cups are capable of attaching the light emitting device to appropriate fixtures or vehicles on the outside and elsewhere. Moreover, the outer cylinder  200  prevents the inside of the light emitting device from the invasion of insects and rainwater or the like. The detailed explanation is omitted because the structures other than these is practically identical to the fifth embodiment described above. 
     Next, the light emitting device pertaining to the seventh embodiment of this invention is explained in accordance with FIG.  12  and FIG.  13 . In this embodiment, a flexible substrate (also called a flexible printed circuit board)  420  is used as a main plate (main body). Two or more pairs of electrodes  461  and  462  are regularly arranged in the substrate  420 . A film of aluminum (not shown in the figure) is fixed by deposition (CVD, PVD, or the like) on the substrate  420  (the side from which the light is emitted), and the film is designed to reflect the light which goes to the opposite side. Moreover, an uncovered LED element  430  is used as an LED element or source of light in this embodiment. In the each of the above embodiments, the LED elements were one of the usual type, which are sealed with transparent resin covering the outside of the diode. In the seventh embodiment, LED elements in which the ordinary sealing materials are removed are used. One side of the PN junction of LED element  430  is electrically connected to the electrode  461  of the substrate  420  through proper conductive materials such as solder. The other side of the LED element is electrically connected to the electrode  462  through bonding wire  464 . Optional conductive materials can be used as the bonding wire  464 . Here, the direction of the light emitted from the LED elements is adjusted to be in the upper direction shown on FIG. 12 (the direction towards the scattering plate). In addition, in this embodiment, the first light scattering plate  460  sealing the LED element  430  from outside is used. More concretely, the first light scattering plate  460  is designed to completely enclose the LED element  430 . Striations forming prisms as explained in the above embodiments are made on the upper side of the first light scattering plate  460  (as shown on FIG.  12 ). The first light scattering plate is molded and hardened by pouring the resin into a suitable mold after the completion of fixation and wiring of LED element  430 . The second light scattering plate  470  is arranged above the upper side of the first light scattering plate  460  (as shown on FIG.  12 ). The structure of this second light scattering plate  470  is basically the same as that of the above-described embodiments. However, it is preferable to use flexible materials for the first and second light scattering plate. 
     As shown in FIG. 14, the striations forming prisms on the bottom, surface of the second light scattering plate  470  are shaped such that the top of the bottom side  470   a  has a sectional arc shape and the top of the upper side of  470   b  has a sectional acute angle (here, acute angle does not mean that this is not an obtuse angle but does mean that a clear peak exists.) Similarly, the shape of the striations forming prisms on the top surface of the first light scattering plate  460  is the inverse of that of FIG.  14 . In other words, the tops of the upper side are sectional arcs and those of the bottom side are sectional acute angles. 
     The light emitting device in the seventh embodiment has the advantage of enabling the shape to be changed to that of the part of application as required because the main plate  420  is composed of a flexible substrate. 
     Moreover, the total thickness of the light emitting device can be reduced in this embodiment, because of the structure wherein the LED element  430  does not have a cover (refer to FIG.  12 ). 
     In addition, in the light emitting device of this embodiment, the LED elements  430  are protected by the first light scattering plate  460  because it seals the LED elements with respect to the outside. Moreover, the first light scattering plate which serves both for sealing the LED elements and scattering light results in thinning the total thickness of the device furthermore. 
     The detailed explanation is omitted because the structure other than these is practically the same as the fourth embodiment described above. 
     Each previous embodiment has been an example of using two scattering plates. However, more than two plates can be also used. Moreover, plate-shaped scattering device have been given as examples. However, sheet-shaped scattering devices are also acceptable. In this case, this invention also can be applied to lighting of display boards for indicator panels, and to use as backlights for liquid crystal displays in the case of a sheet shape. 
     While preferred embodiments of the present invention have been set forth in detail above, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. Therefore, the present invention should be construed as being limited only by the appended claims.