The present disclosure relates to an illumination device, and specifically, to an illumination device capable of obtaining a smooth emergent light intensity distribution.

Background Art Recently, point light sources such as an LED are more and more frequently applied to illumination devices. Fig. 1A and Fig. IB show a downlight 1 as one example of the illumination devices using a point light source, wherein Fig. 1A is a sec ^¬ tional view of the downlight 1, and Fig. IB is a top view of the downlight 1. Referring to Fig. 1A and Fig. IB, the downlight 1 comprises a housing 11 comprising a bottom portion and a side wall portion, and a plurality of LEDs 12 ar ^¬ ranged on the bottom portion of the housing 11 and emitting light of different colors, wherein the plurality of LEDs 12 are arranged on the bottom portion of the housing 11 in such a manner that they form a circle.

In the example shown in Fig. 1A and Fig. IB, the plurality of LEDs 12 are separately disposed at different positions on the bottom portion of the housing 11. Each LED 12 forms light spots at different positions on an illuminated surface, in accordance with its location and the luminous intensity dis ^¬ tribution. These light spots partially overlap, and as a re ^¬ sult, the light intensity distribution curve on the illumi ^¬ nated surface S is not smooth, and the user may observe glare, chromatic aberration or bright-dark change on the il- luminated surface S .

Moreover, when a barrier B exists between the downlight 1 and the illuminated surface S, the plurality of LEDs 12 emitting light of different color illuminate the barrier B, and pro- duce shadows on the illuminated surface S. Since the plural ^¬ ity of LEDs 12 are separately disposed at different positions on the bottom portion of the housing 11, the different LEDs 12 will produce shadows at different positions on the illumi ^¬ nated surface S. These shadows partially overlap, and as a result, as shown in Fig. 1A, multiple shadows are formed on the illuminated surface S, which deteriorates the illumina ^¬ tion effects of the downlight 1.

As a solution for solving this problem, an illumination device using a diffuser has been proposed. Fig. 2 shows a downlight 2 as one example of illumination devices comprising a point light source and a diffuser. Referring to Fig. 2, the downlight 2 comprises a housing 21 comprising a bottom portion and a side wall portion, and a plurality of LEDs 22 disposed on the bottom portion of the housing 21 and emitting light of different colors, wherein the plurality of LEDs 22 are arranged on a PCB board 23 on the bottom portion of the housing 21 in such a manner that they form a circle. The downlight 2 further comprises a diffuser 24 located on the light emergent side. By providing the diffuser 24, the light emitted from the plurality of LEDs 22 are mixed, which en ^¬ hances the smoothness of light intensity distribution curve of the light emerging from the downlight 2.

However, in the case of using the diffuser 24, a portion of the light emitted from the plurality of LEDs 22 is lost due to the diffuser 24. Moreover, since the diffuser 24 has a small thickness, the light mixing effect thereof is limited. Further, it is also difficult for the downlight 2 to obtain a narrow beam angle.

Therefore, it is desirable to provide an illumination device having high luminous efficiency and capable of obtaining a smooth emergent light intensity distribution (without produc ^¬ ing multiple shadows) .

Summary of the invention

An illumination device according to an embodiment of the pre ^¬ sent technique comprises: a housing comprising a bottom por- tion and a side wall portion; a light guide plate provided on the bottom portion of the housing and comprising a side surface, a first surface, and a second surface facing the first surface, the second surface being closer to the bottom por ^¬ tion of the housing than the first surface; and a plurality of light sources provided on the side surface of the light guide plate and emitting light to the side surface, the light emerging from the first surface of the light guide plate to the outside, after travelling in the light guide plate.

By providing the light guide plate, the illumination device according to an embodiment of the present technique can mix the light from the plurality of light sources with a very small light loss. Thus, the illumination device can maintain high luminous efficiency, and obtain a smooth emergent light intensity distribution, without producing multiple shadows. Preferably, a plurality of convex-concave structures are formed on the second surface of the light guide plate.

In the case where a plurality of convex-concave structures are formed on the second surface of the light guide plate, the light mixing effect of the light guide plate can be ad ^¬ justed by setting the size, density, arrangement, etc. of the plurality of convex-concave structures, so as to obtain the desired emergent light intensity distribution. For example, preferably, the plurality of convex-concave structures can be designed such that the first surface of the light guide plate has a Gaussian emergent light intensity distribution .

In such case, the illumination device has a smooth emergent light intensity distribution (Gaussian emergent light inten ^¬ sity distribution) , and thereby, the occurrence of multiple shadows can be avoided despite the use of the plurality of light sources for illumination. Thus, excellent illumination effects are achieved. Preferably, the size of the convex-concave structure de ^¬ creases as a distance between the convex-concave structure and the center of the light guide plate increases, or the density of the plurality of convex-concave structures de ^¬ creases as the distance between the convex-concave structures and the center of the light guide plate increases.

Thus, the desired emergent light intensity distribution can be obtained by adjusting the size and density of the convex- concave structures.

Preferably, the convex-concave structure can be a dot-like convex structure or a dot-like concave structure.

In such case, it is possible to form the convex-concave structure in a simple manner, for example, the convex-concave structure can be formed on the second surface of the light guide plate by an inkjet printing method or a mechanical en ^¬ graving method, or the convex-concave structure can be formed integrally with the light guide plate by an injection molding method or a press molding method. Similarly, the convex-concave structures can be designed such that the first surface of the light guide plate has a smooth curved emergent light intensity distribution in which the center is higher than the circumference or the center is lower than the circumference. Further, according to the needs of design, the convex-concave structure can be designed such that the first surface of the light guide plate has an emergent light intensity distribu ^¬ tion of other type.

According to the needs of design, the light guide plate can have, in a top view, a circular shape, an elliptical shape, a rectangular shape, or a regular hexagonal shape.

Preferably, the plurality of light sources are uniformly dis ^¬ tributed around the light guide plate. Preferably, the plu ^¬ rality of light sources include red light sources, blue light sources and green light sources. Preferably, the plurality of light sources are point light sources such as LEDs and la ^¬ ser diodes.

Preferably, the bottom portion and/or the side wall portion of the housing have a function of specular reflection or dif- fuse reflection.

In such case, the luminous efficiency of the illumination de ^¬ vice can be further enhanced. Brief Description of the Drawings

Fig. 1A and Fig. IB are respectively a sectional view and a top view of an example of the illumination devices according to relevant techniques; Fig. 2 is a diagram showing another example of the illumina ^¬ tion devices according to relevant techniques;

Fig. 3A and Fig. 3B are respectively a sectional view and an oblique view of an example of the illumination device accord ^¬ ing to the implementation of the present technique; Fig. 4A and Fig. 4B are respectively an oblique view and a top view of an example of the light guide plate according to the implementation of the present technique;

Fig. 5A is a schematic diagram of an optical path example of the illumination device according to the implementation of the present technique; and Fig. 5B is a schematic diagram of an optical path of the illumination device according to relevant techniques;

Fig. 6 is an optical simulation diagram of the optical path example of the illumination device according to the implemen- tation of the present technique;

Fig. 7 is an optical simulation diagram of an illumination distribution example of the illumination device according to the implementation of the present technique; and

Fig. 8 is a diagram of examples of emergent light intensity distribution of the illumination device according to the implementation of the present technique. Detailed Description of the Embodiments

In the following detailed description, some exemplary embodiments of the present technique are described with reference to the accompanying drawings which form a part hereof. It is to be understood that other embodiments may be utilized and various changes may be made without departing from the scope of the present technique. The following detailed descrip ^¬ tion, therefore, is not to be taken in a limiting sense, and the present technique is defined by the appended claims. Fig. 3A and Fig. 3B schematically illustrate an illumination device 3 according to the implementation of the present technique, wherein Fig. 3A is a sectional view of the illumina ^¬ tion device 3, and Fig. 3B is an oblique view of the illumi ^¬ nation device 3. Referring to Fig. 3A and Fig. 3B, the illu- mination device 3 comprises a housing 31, a plurality of LEDs 32 and a light guide plate 33.

The housing 31 comprises a bottom portion 311 and a side wall portion 312 extending from the circumference of the bottom portion 311 towards the outside. Preferably, the surface of the bottom portion 311 and/or the surface of the side wall portion 312 have a function of specular reflection or diffuse reflection, so as to enhance light extraction efficiency.

The plurality of LEDs 32 are disposed on the bottom portion 311 of the housing 31. The plurality of LEDs 32 can be ei- ther supported by a single support member such as a PCB board, or supported by respective support members. The plu ^¬ rality of LEDs 32 include LEDs emitting light having differ ^¬ ent colors, e.g., including LEDs emitting red light, green light and blue light. The light guide plate 33 is disposed on the bottom portion 311 of the housing 31. In the present embodiment, the light guide plate 33 has a circular shape in the top view, and the plurality of LEDs 32 are uniformly disposed around the light guide plate 33. In the case where the plurality of LEDs 32 include LEDs emitting light having different colors, the LEDs emitting light having different colors can be arranged around the light guide plate 33 in a predetermined sequence, for ex ^¬ ample, in a sequence of red LED, green LED, blue LED, red LED

Referring to Fig. 4A and Fig. 4B, a plurality of dot-like convex structures 331 are provided on the lower surface (the surface of the light guide plate 33 on the side of the bottom portion 311 of the housing 31) of the light guide plate 33. The plurality of dot-like convex structures 331 are arranged on the lower surface of the light guide plate 33 in a manner of central symmetry, and the symmetry center is the center of the lower surface of the light guide plate 33. In the pre ^¬ sent embodiment, the size and density of the plurality of dot-like convex structures 331 decrease as the distance be ^¬ tween the dot-like convex structures 331 and the center of the lower surface of the light guide plate 33 increases.

The plurality of dot-like convex structures 331 can be formed on the lower surface of the light guide plate 33 by an inkjet printing method or a mechanical engraving method, or the plu ^¬ rality of dot-like convex structures 331 can be formed inte ^¬ grally with the light guide plate 33 by an injection molding method or a press molding method.

Fig. 5A shows an optical path example of the illumination de- vice 3 according to the implementation of the present technique, and as a contrast, Fig. 5B shows an optical path of the illumination device 1 according to relevant techniques as shown in Fig . 1.

Referring to Fig. 5A, in the illumination device 3 according to the present embodiment, the light emitted by the plurality of LEDs 32 is incident upon the light guide plate 33 via the side surface of the light guide plate 33, and emerges from the upper surface of the light guide plate 33 after being to ^¬ tally reflected for many times via the upper surface and the lower surface of the light guide plate 33 and sufficiently mixed. A portion of the emergent light directly emerges to the outside of the illumination device 3, and the other por ^¬ tion of the emergent light emerges to the outside after being reflected by the inner surface of the side wall portion 312 of the housing 31. Since the plurality of dot-like convex structures 331 are provided on the lower surface of the light guide plate 33, the light inside the light guide plate 33 is totally re ^¬ flected at the plurality of dot-like convex structures 331. Further, since the plurality of dot-like convex structures 331 are arranged in a predetermined manner, the light inside the light guide plate 33 undergoes different total reflec ^¬ tions at different positions on the lower surface of the light guide plate 33, and thereby, the desired light inten ^¬ sity distribution is obtained on the upper surface of the light guide plate 33.

In the present embodiment, since the size and density of the plurality of dot-like convex structures 331 decrease as the distance between the dot-like convex structures 331 and the center of the lower surface of the light guide plate 33 in- creases, the maximum light intensity is obtained at the cen ^¬ ter of the upper surface of the light guide plate 33, and the minimum light intensity is obtained in the vicinity of the edge of the upper surface of the light guide plate 33. Fur ^¬ ther, since the size and density of the plurality of dot-like convex structures 331 gradually decrease, a light intensity distribution curve with smooth transition is obtained between the center and the vicinity of the edge of the upper surface of the light guide plate 33.

However, in the illumination device 1 of relevant techniques, referring to Fig. 5B, a plurality of LEDs 12 separately emit light to the outside of the illumination device 1, each LED 12 form light spots at different positions on an illuminated surface, and these light spots partially overlap each other. As a result, the light intensity distribution on the illumi ^¬ nated surface does not have a curve with smooth transition. Fig. 6 is an optical simulation diagram of the optical path example of the illumination device according to the implementation of the present technique. Fig. 7 is an optical simu ^¬ lation diagram of an illumination distribution example of the illumination device according to the implementation of the present technique.

Referring to Fig. 6 and Fig. 7, in the present embodiment, Gaussian emergent light intensity distribution is obtained on the upper surface of the light guide plate 33. Specifically, as shown in Fig. 7, the maximum illumination of about 2000 Lux is obtained at the center of the upper surface of the light guide plate 33, as the distance from the center in ^¬ creases, the illumination gradually (smoothly) decreases, and the minimum illumination of about 200 Lux is obtained in the vicinity of the edge of the upper surface of the light guide plate 33. Thus, the illumination device 3 according to the present em ^¬ bodiment can obtain smooth emergent light intensity distribu ^¬ tion while maintaining high luminous efficiency, which avoids the occurrence of multiple shadows. Moreover, due to the light mixing effect of the light guide plate 33, the occur ^¬ rence of glare is reduced.

In the illumination device 3 according to the present embodi ^¬ ment, when the plurality of LEDs 32 include LEDs emitting light having different colors, by means of the light mixing effect of the light guide plate 33, superior color mixing ef ^¬ fect can be achieved.

The example in which a plurality of LEDs 32 are used as the light source is described as above. However, the present technique is not limited to this. The illumination device according to the present technique can include light sources in other forms, for example, point light sources, linear light sources or area light sources such as laser diodes, as long as the light emitted therefrom can be effectively guided into the side surface of the light guide plate 33. The plurality of LEDs 32 are side-emission type LEDs. How ^¬ ever, the present technique is not limited to this. In the illumination device according to the present technique, a light source of top-emission type can also be used, as long as light guide means such as a mirror or a prism is provided on its light emitting surface to effectively guide the light emitted therefrom into the light guide plate.

The example in which a plurality of dot-like convex struc ^¬ tures 331 are used as the plurality of convex-concave struc ^¬ tures on the lower surface of the light guide plate 33 is de- scribed as above. However, the present technique is not lim- ited to this. In the illumination device according to the present technique, a plurality of dot-like concave structures can be provided on the lower surface of the light guide plate, and the same effect can be achieved. The plurality of convex-concave structures do not necessarily have a circular bottom surface as the dot-like convex structures 331 shown in Fig. 4B, and optionally, they can have an elliptical bottom surface, a triangular bottom surface, or a rhombic bottom surface. In addition, in the illumination device according to the present technique, the plurality of convex-concave structures are not necessarily formed as dot-like structures as shown in Fig. 4B, and they can have a shape such as a stelliform or helical linear shape, and a concentric wave shape .

In the above embodiment, the size, density, and arrangement of the plurality of dot-like convex structures 331 on the lower surface of the light guide plate 33 are designed such that the first surface of the light guide plate 33 has a Gaussian emergent light intensity distribution. However, the present technique is not limited to this. For example, in the illumination device according to the present technique, the plurality of convex-concave structures on the lower sur ^¬ face of the light guide plate can be designed such that the upper surface of the light guide plate has a smooth curved emergent light intensity distribution in which the center is higher than the circumference or the center is lower than the circumference, or has other desired emergent light intensity distribution .

Fig. 8 shows three examples of emergent light intensity dis- tribution of the illumination device according to the implementation of the present technique. As shown in Fig. 8, in Fig. (a), the emergent light intensity distribution in which the center is higher than the circumference is obtained; and in Fig. (b) , the emergent light intensity distribution in which the center is lower than the circumference is obtained. Moreover, in Fig. (a) and Fig. (b) , the emergent light inten- sity distribution is in a smooth transition from the center to the circumference. In Fig. (c) , the emergent light inten ^¬ sity distribution which is completely uniform is obtained. In addition, according to the needs of design, various parameters of the plurality of convex-concave structures such as size, density, and arrangement can be appropriately set, in order to obtain the desired emergent light intensity dis ^¬ tribution .

Description is made as above by taking the case in which the light guide plate 33 has a circular shape in the top view as an example. However, the present technique is not limited to this. For example, the light guide plate can also has, in the top view, an elliptical shape, a rectangular shape, or a regular hexagonal shape, which can be appropriately set in accordance with the needs of design. It is to be understood that the features of the various exem ^¬ plary embodiments described herein may be combined with each other, unless specifically noted otherwise.

In addition, while a particular feature or aspect of an embodiment of the present invention may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other fea ^¬ tures or aspects of the other implementations as may be de ^¬ sired and advantageous for any given or particular applica ^¬ tion. Although specific embodiments have been illustrated and de- scribed herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equiva ^¬ lent implementations may be substituted for the specific em ^¬ bodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific em ^¬ bodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equiva ^¬ lents thereof.

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List of reference signs

I, 2, 3 illumination device

II, 21, 31 housing

12, 22, 32 LED

311 bottom portion

312 side wall portion

33 light guide plate

331 dot-like convex structure