Abstract:
A refraction-type LED ceiling lamp, especially a plate-type ceiling lamp which is used on an indoor ceiling, includes primarily a fiber light guide plate, a reflection surface of which is provided with multiple chip-shape reflection elements, distributed in arrays. A chip size of the reflection elements decreases gradually toward an entrance surface by a geometric series; whereas, a gap between the reflection elements increases gradually. A reflection curve of the reflection element allows light to be projected out uniformly and a required illumination angle to be achieved.

Description:
BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     The present invention relates to a refraction-type LED (Light Emitting Diode) ceiling lamp, and more particularly to a plate-type ceiling lamp which is used on an indoor ceiling with a limited projection angle to project brilliance on a limited area on a ground, forming uniform light beams of emission and effectively defining a projection area. In addition, the ceiling lamp can be assembled on the ceiling successfully and can be cooled spontaneously. 
     b) Description of the Prior Art 
     In a wave of saving energy and reducing carbon dioxide emission, energy-saving illumination equipment has become a mainstream in household or office illumination. A fluorescent light and an LED lamp can save energy, yet as an existing LED lamp is deployed as a dot-matrix distribution, the LED lamp is a point source of light in the dot-shape distribution if viewing from outside. In addition, due to an error in a manufacturing process or of a material, each LED lamp will have a different illumination efficiency and wavelength, and a color render index of the LED lamp will be inferior. Whereas, a conventional fluorescent light is provided with uniform brightness, and the color render index and intensity of illumination are uniform and soft by a new three-wavelength technology. Therefore, for an implementation using the LED as an illumination element, light beams should be transformed through an optical mechanism so as to be applied to indoor illumination. 
     In general, a quantity of illumination devices is determined by a floor space size in a room. For example, an office of about 6-8 m 2  (meter) will require 100 W (watt) of illumination equipment for reading and an illumination angle should be less than 180° in principle, whereas the illumination angle is set at 180° for the illumination equipment that is provided with a directionality function so as to define a specific illumination angle for an illumination area. Although utilization of light energy can be satisfied through defining the illumination angle to prevent from unnecessary loading to the light energy, it is difficult to define the illumination angle for an ordinary lamp-set. 
     An LED illumination business has been recognized as one of the promising businesses in recent years, mainly due to a small size and light weight. If the LED can be applied to illumination, a household space will be provided with a more flexible utilization mode and an effect of energy-saving can be expected. The LED is small in size and has a fast response time, and does not have a danger of mercury in the conventional fluorescent light; these are all the advantages of the LED. However, the LED that is applied in the household illumination should operate at a high power; hence, waste heat will be generated correspondingly. In addition, a working temperature of an LED lamp-set system cannot be too high and a total temperature difference should not be higher than 15° to prevent from thermal strain degradation of material by heat or prevent the material from undergoing a vicious cycle by a resistance factor that the efficiency is lost. If the lost of efficiency exceeds 10%, then the brilliance of projection will decrease explicitly, which largely reduces a total lumen of light flux at the projection area. 
     An existing LED illumination design includes U.S. Pat. No. 6,540,373 B2 disclosing a slab on which multiple LED excitation units are arranged in a matrix. The slab is one of the plates forming a ceiling and therefore, light can be emitted downward. However, as the excitation unit is a point source of light, appearance will offend eyes and lumen or a color temperature will be non-uniform due to the manufacturing error. 
     In U.S. Pat. No. 6,355,961 B1, a projection surface of the LEDs, arranged in a matrix, is provided with a photo-rectifier to dissipate light spots, and in another U.S. Pat. No. 7,311,423 B2, a location where a conventional fluorescent light resides is replaced with an LED, having a same issue of an explicit point source of light. 
     In terms of a light beam modulation technology, there is US Publication No. 2001/0046131 A1 wherein a mixing chamber is utilized to reflect a light beam operation part, with the light beam being pre-expanded through a diffuser assembly and then entering into a light guide plate. In addition, a direction of the light beam is changed at a reflection surface to serve as backlit for an LED board. This invention is utilized in a different situation and the methods of pre-mixing and pre-diffusing are employed. Therefore, a light flux has been lost significantly before entering into the light guide plate in spite that when the light beam is used for the LED backlit, the brightness is very uniform. Nevertheless, for the indoor illumination that focuses on the energy saving, the loss from the light beam pre-transformation operation does not facilitate a general implementation. 
     SUMMARY OF THE INVENTION 
     With the principles of light reflection and refraction, the present invention utilizes angle guidance and a reflection design which corresponds with an unequal optical path to allow a ceiling lamp to have an effect of uniform intensity of illumination and lumen, to define a projection area and to effectively utilize a light flux. 
     The present invention utilizes a slab-shape light guide plate, with at least two parallel and opposite entrance surfaces to allow light beams generated from a series of excitation units to enter into the light guide plate oppositely. The light guide plate is formed with a refraction surface to emit the light beam and with another surface which is a reflection surface. The reflection surface is provided with plural reflection elements which are arranged in a matrix. A chip size of the reflection element decreases gradually by a geometric series toward the entrance surface, from a breadth center; whereas a gap between the reflection elements increases gradually by a geometric series. In principle, the chip size of the reflection elements at the breadth center is 2, gradually decreasing to 1 for the chip size of the reflection elements at a periphery of the breadth. On the other hand, the gap between the reflection elements at the center of the reflection breadth is 1, gradually increasing to 2 for the gap between the reflection elements at the periphery of the breadth. To allow the light beams that are emitted from the excitation units to be depleted gradually when the beams reach to the center in progression of the optical path, a density of the reflection elements can be increased at the center to forcefully enhance the reflection operation, enabling the lumen of the light beams emitted from the entire refraction surface to be uniform. The reflection element is in a convex shape and is provided with an inward reflection curve. The reflection element can change a direction of and reflect the light beam emitted by the excitation unit at a fixed angle into a vertical line close to the refraction surface, such that the optical path of the excitation unit is bended by about 90°. Therefore, in terms of the illumination angle, the ceiling lamp can be effectively defined as projecting downward to guide the light flux to illuminate downward in full intensity approximately. 
     The present invention focuses on an effective utilization of directionality of the total light flux, allowing the light beams to be emitted uniformly for the entire refraction surface and effectively dissipating the waste heat of the excitation units. Accordingly, a fiber light guide plate is designed, wherein at least two parallel entrance surfaces provide a corresponding design of the excitation units arranged in a series, with light energy generated by the excitation units entering from the entrance surfaces at two parallel sides, being reflected and traveling forward in the light guide plate. The light beams that enter into the entrance surfaces are divided into multiple orientations and basically, a size of the light guide plate can be chosen according to the emission angle of the excitation unit. For an ordinary LED excitation unit, the emission angle is between 20° and 60°. After the emitted light beam has entered from the entrance surfaces of the light guide plate, a part will operate on the refraction surface, whereas other part will operate on the reflection surface. After reaching the reflection surface, the light beam is reflected according to a normal of the reflection surface to travel toward the refraction surface. On the other hand, the reflection surface is provided with the reflection elements which are provided with the reflection curves. The reflection curve corresponds to the light beam that enters from the entrance surface and is bended effectively, allowing an emission route refracted from the reflection beam to approach to a vertical line of the refraction surface, thereby transforming the light beam generated by the excitation unit by about 90°. Therefore, the illumination angle of the ceiling lamp can be oriented effectively to define a limited angle, the light flux will not be loaded unnecessarily, and a frame of the excitation unit can be utilized directly as a heat conduction mechanism to effectively dissipate the waste heat generated, with an assembly part being formed by utilizing the frame to facilitate installing on the ceiling to illuminate on a ground. In addition, the uniform brightness can be achieved and the illumination angle can be defined, which are the primary object of the present invention, by arranging the reflection elements on the reflection surface in a matrix, with the gap increasing gradually by a geometric series from the center and the chip size of the reflection elements decreasing gradually from the center. 
     Another object of the present invention is that the frame, which is provided with a locking function, provides for the serial arrangement of the excitation units and fixes the light guide plate through an assembly method. 
     A third object of the present invention is that an exterior surface of the reflection surface of the light guide plate is provided with a reflection plate which reflects inward, and the refraction surface can be provided outward more with a light diffuser plate which can be further configured as a brightness enhancing plate (brightness enhancing film). 
     To enable a further understanding of the said objectives and the technological methods of the invention herein, the brief description of the drawings below is followed by the detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of the present invention which is applied to an indoor ceiling. 
         FIG. 2  shows a side cutaway view of structures of the present invention. 
         FIG. 3  shows a side view of a working principle of light beam of the present invention. 
         FIG. 4  shows a schematic view of illumination angles of the present invention. 
         FIG. 5  shows a schematic view of a distribution of reflection elements which are arranged, according to the present invention. 
         FIG. 6  shows a schematic view of a relative optical path of a reflection element, according to the present invention. 
         FIG. 7  shows illuminance curves at 1.6 m of an optical path of the present invention. 
         FIG. 8  shows illuminance curves at 2 m of an optical path of the present invention. 
         FIG. 9  shows curves of illuminance measured along an X-axis on an area at 1.6 m of an optical path, of the present invention and a conventional fluorescent lamp. 
         FIG. 10  shows curves of illuminance measured along a Y-axis on an area at 1.6 m of an optical path, of the present invention and a conventional fluorescent lamp. 
         FIG. 11  shows curves of illuminance measured along an X-axis on an area at 2 m of an optical path, of the present invention and a conventional fluorescent lamp. 
         FIG. 12  shows curves of illuminance measured along a Y-axis on an area at 2 m of an optical path, of the present invention and a conventional fluorescent lamp. 
         FIG. 13  shows a schematic view of frames of the present invention being directly implemented as a heat dissipation mechanism. 
         FIG. 14  shows a schematic view of the present invention, wherein excitation units are implemented on two opposite sides to form projection areas. 
         FIG. 15  shows a schematic view of the present invention, wherein excitation units are implemented on multiple opposite sides to form projection areas. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a ceiling lamp  10  of the present invention is applied to an indoor ceiling, e.g. of a configuration with light-weight steel frames  8 . The ceiling lamp  10  has a same area as a partition panel  80  and therefore can be easily assembled at the light-weight steel frame  8  to form illumination on a ground. 
     Referring to  FIG. 2 , the ceiling lamp  10  of the present invention comprises primarily a light guide plate  1 , wherein two opposite sides are parallel to each other and are formed respectively with an entrance surface  100 , an exterior part of the entrance surface  100  is provided correspondingly with an LED excitation unit  4  which forms a series, and an exterior part of which is a heat conduction unit  5  to expel waste heat, forming a waste heat dissipating path. Lower and upper sides of the light guide plate  1  are formed respectively with a refraction surface  12  and a reflection surface  11 . A light beam generated by the excitation unit  4  enters from the entrance surface  100 , and then is reflected and travels forward inside a space between the refraction surface  12  and the reflection surface  11 . 
     An exterior of the reflection surface  11  can be provided with a reflection plate  2 , and an upper frame  61  and a lower frame  62  of a frame  6  can be used to clamp the heat conduction unit  5 , the LED excitation unit  4 , the light guide plate  1 , a light diffuser plate  3  and the reflection plate  2  which are finally fixed by an assembly element  60 . After dismantling the assembly element  60 , the upper frame  61 , the ceiling lamp  10  and the heat conduction unit  5  can be separated, so as to facilitate repairing the excitation unit  4 . 
     At least one side of the frame  6  is provided with an assembly part  66  for assembling with an exterior part, such as by hanging or crossing-over. 
     Referring to  FIG. 3 , an essential working principle of the light beam of the present invention is that a light beam B 0  emitted by the LED excitation unit  4  enters from the entrance surface  100  of the light guide plate  1 , followed by traveling forward from being reflected on the reflection surface  11  and part of the beam B 0  traveling forward from being reflected inward, between the reflection surface  11  and the refraction surface  12 . The light beam B 0  is set up by a manufacturing specification of an illumination chip  41  of the excitation unit  4 . For example, for an angle of 60°, the light beam emitted will enter from the entrance surface  100  at 60°. In addition, the illumination chip  41  is assembled on a substrate  42 , allowing multiple illumination chips  41  to be arranged in a series. 
     After the light beam B 0  generated by the LED excitation unit  4  has entered from the entrance surface  100 , a light beam B 1  will operate on the reflection surface  11  and a reflection beam B 10  will be resulted according to a normal n of the reflection surface  11 , whereas part of the light beam B 1  will result in a refraction beam B 1t  due to reflection loss of the reflection surface  11 . The refraction beam B 1t  can be reflected again by a reflection surface  20  provided on an interior surface of the reflection plate  2  to reflect a feedback beam B 1r  toward the light guide plate  1 . Therefore, for the light beam B 1  which enters from the light beam B 0 , there will be the aforementioned reflection beam B 10  and feedback B 1r , or a partial beam B 2  which will operate on the refraction surface  12 . As the refraction surface  12  can be further provided with a higher refraction rate, small part of the beam will form an internal reflection beam B 20  as a traveling light; whereas, a light beam which comes out from the light beam B 2  through the operation of the refraction surface  12  is a refraction beam B 2t  which is one of the light beams for illumination. 
     Another light beam B 3  which enters from the entrance surface  100  will operate on a reflection element  13  which is provided with an inward reflection curve  130 . The reflection curve  130  will form an interior reflection and result in a reflection beam B 30  according to a normal n of curvature. The reflection beam B 30  changes a direction significantly to alter a traveling orientation of the light beam B 0  which is transmitted from the excitation unit  4 , allowing the reflection beam B 30  to be close to a vertical line L 0  of the refraction surface  12 , thereby defining an illumination angle θ (as shown in  FIG. 4 ). 
     By the operation of that reflection beam B 30 , the light beams can be largely concentrated to be close to the vertical line L 0  of the refraction surface  12 , defining a light flux as downward emission, such that a total light flux can be used effectively without being depleted horizontally. 
     On the other hand, when the reflection beam B 30  operates on the refraction surface  12 , part will be reflected as a reflection beam B 3r , and part will form a refraction beam B 3t  when passing through a different medium. As the refraction beam B 3t  is formed from a rarefaction-compression process, the beam B 3t  will deviate from the normal n, but this deviation will not explicitly affect the projection angle. 
     The refraction beam B 3t  and the aforementioned refraction beam B 2t  are all the light beams used for illumination. An exterior surface of the refraction surface  12  of the light guide plate  1  can be provided with the light diffuser plate  3  which further diffuses the refraction beams B 3t , B 2t . Accordingly, for illumination beams B n  formed, brightness will be more uniform, and the light diffuser plate  3  can be an optical diffusion material or a brightness enhancing film. 
     The reflection element  13  is convex and protrudes out of the upper surface of the light guide plate  1 . In principle, the light guide plate  1  is an optic fiber to guide light, and the reflection surface  11  and the refraction surface  12  formed are all capable of internal reflection. The reflection element  13 , on the other hand, is assembled on the exterior surface of the reflection surface  11  of the light guide plate  1  by ink printing or being formed integrally. 
     If the reflection element  13  is formed by the optic ink printing method, then an assembly interface  131  will form a pattern to damage structures, allowing the reflection surface  11  within the assembly interface  131  to lose the capability of reflection. Therefore, after the light beam B 0  has entered, and before the traveling beam B 3  has operated on the reflection curve  130 , a scattering effect will be formed and uniformly operate on the entire inner curve of the reflection curve  130  through the assembly interface  131 , with the inner curve reflecting out the reflection beam B 30  directionally. Accordingly, the damage condition of the assembly interface  131  can determine an intensity of the reflection beam B 30  in a single path, and the reflection beam B 30  can be pre-diffused to form more reflection of uniform orientation, with the light beam B 30  being emitted out through the refraction surface  12 . 
     The light diffuser plate  3  is a diffusing device and will carry out secondary diffusion to the light beams that are refracted from the light guide plate  1 ; hence, the light beams that are projected from the entire projection surface of the light guide plate  1  can have a fine and uniform distribution in appearance. 
     According to experiments of the present invention, the brightness of illumination and the uniform intensity of illumination can all satisfy or even exceed a bed side fluorescent lamp, including a fluorescent light, a PL lamp or a T5 light tube. The experiment material used in the present invention is a single LED of 1 W, with the total illuminance measured being 13,460 LUX at a center of the surface, 1,100 LUX at a center of 1.2 m of optical path, and 510 LUX at a center of 1.6 m of optical path. 
     The features that the single LED shows are low power loss, uniform surface brightness and an extremely high efficiency. In addition, the structure is firm and a shape is light-weight and thin, which can be applied indoor, to an office or a special work condition, and can be even used for high brightness advertisement illumination in a public space. 
     The present invention transforms the light beams, with the effect that the light beams generated by the LED can be deflected directly and diffused uniformly. In addition, as the LEDs used are not too many, energy consumption will be reduced correspondingly. Moreover, according to an ordinary circuit application, the present invention can be set as remote controlling, the brightness can be adjusted, a color wave can be changed or a color temperature can be adjusted. As these kinds of adjustments belong to an ordinary circuit modulation technology, further description is not provided. Basically, by fitting with these adjustments and inherent features, the present invention can be more suitably accepted by vision of human. 
     Referring to  FIG. 4 , the ceiling lamp  10  of the present invention employs a power supply  7  to gain electricity. After the LED excitation unit  4  has operated, the light beam generated by the excitation unit  4  will be reflected outward from the refraction surface  12 , through the transformation of the light guide plate  1  and the reflection plate  2  or the light diffuser plate  3 . In addition, due to the operation of the reflection element  13 , the illumination angle of the ceiling lamp  10  can be defined at a certain degree θ, allowing the total light flux to be concentrated in θ and to be projected on the ground. Moreover, when a projection distance is set at 1.6 m or 2.0 m, the intensity of illumination can be better satisfied and compatible with a fluorescent light. 
     Referring to  FIG. 5 , the protruded reflection element  13  (as shown in  FIG. 3 ) that is provided on the reflection surface of the light guide plate  1  can be implemented by printing or integrally formed with the light guide plate  1 . Basically, the reflection element  13  is a round and convex spherical body, assembled at a side of the reflection surface  11 . For the array arrangement of the reflection element  13 , in order to allow a breadth center of the light guide plate  1  to have a higher probability of reflection, a concept of shape expanding and a method of distribution in a narrow gap are employed, such that an equal transformation effect can be available in an optical path L which is resulted from the LED excitation unit  4 . The configuration of the reflection element  13  is based on the breadth center of the light guide plate  1 , where the reflection elements  13  provided in the breadth center are larger, with a chip size decreasing outward gradually by a geometric series, which can further allow the chip size of the reflection elements  13  in the breadth center to be 2 times that the chip size of the reflection elements  13  close to the entrance surface  100 . 
     On the other hand, a distance between neighboring reflection elements  13  is a relative distance on a circumference of each reflection element  13 , with a gap of L 1  at the breadth center increasing gradually outward by a geometric series, to a relative gap of L 2  between the neighboring reflection elements  13  close to a side of the entrance surface  100 . In addition, the gap L 2  can be set as twice the gap L 1 . Therefore, in the optical path L, the light beams generated by the excitation unit  4  can be reflected more toward the center, such that weaker energy close to the center of the optical path can be concentrated in quantity and intensity, while the illumination beams emitted from the refraction surface  12  are equal. 
     Referring to  FIG. 6 , for the aforementioned arrangement of the reflection elements  13  on the breadth of the light guide plate  1 , it is preferred that a linear position of the reflection element  13  faces exactly toward a path of light beam B emitted by the LED excitation unit  4 . 
     Referring to  FIG. 7  and  FIG. 8 , it shows curves of illuminance measured along an X-axis and a Y-axis of a projection area, as well as at projection distances of 1.6 m and 2 m, for an implementation of 48 LEDs of 1 W according to the aforementioned design, under a specification of system power of 110V (volt), 60 Hz (Hertz) and 75 W. 
     Referring to  FIGS. 9 to 12 , it shows curves of illuminance measured along an X-axis and a Y-axis of a projection area under projection distances of 1.6 m and 2 m, for comparing the illumination efficiencies of the present invention with a conventional fluorescent lamp. 
     For specifications of the two aforementioned lamp-sets that are implemented respectively, the ceiling lamp of the present invention operates at 75 W, the conventional fluorescent lamp operates at 90 W, and both operate at a working temperature of 55° C. (Celsius). By comparing the measurement results with the conventional fluorescent lamp, at the projection distance of 1.6 m and 2.0 m respectively, it is found that, within 0 to 1.5 m, the illuminance can satisfy the light flux for reading, and the illuminance is very close to that of the fluorescent lamp and even exceeds the fluorescent lamp at a different axis value. The aforementioned conditions are used for the comparison of the ceiling lamp of the present invention with the conventional fluorescent lamp. 
     The data obtained from the illuminance comparison along the X and Y axes on the projection surface are listed in Table 1 and Table 2. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Z = 1.6 m 
               
             
          
           
               
                   
                 X 
                 LED 
                 Flu. 
                 Y 
                 LED 
                 Flu. 
               
               
                   
                 (cm) 
                 (lux) 
                 (lux) 
                 (cm) 
                 (lux) 
                 (lux) 
               
               
                   
                   
               
             
          
           
               
                   
                 400 
                 14 
                 14 
                 400 
                 14 
                 11 
               
               
                   
                 350 
                 18 
                 19 
                 350 
                 19 
                 16 
               
               
                   
                 300 
                 26 
                 27 
                 300 
                 26 
                 25 
               
               
                   
                 250 
                 38 
                 43 
                 250 
                 39 
                 41 
               
               
                   
                 200 
                 63 
                 77 
                 200 
                 63 
                 71 
               
               
                   
                 150 
                 125 
                 140 
                 150 
                 118 
                 125 
               
               
                   
                 100 
                 255 
                 249 
                 100 
                 253 
                 241 
               
               
                   
                 50 
                 430 
                 413 
                 50 
                 416 
                 397 
               
               
                   
                 0 
                 513 
                 506 
                 0 
                 511 
                 506 
               
               
                   
                 −50 
                 435 
                 416 
                 −50 
                 426 
                 417 
               
               
                   
                 −100 
                 269 
                 248 
                 −100 
                 255 
                 233 
               
               
                   
                 −150 
                 134 
                 130 
                 −150 
                 121 
                 117 
               
               
                   
                 −200 
                 69 
                 68 
                 −200 
                 62 
                 64 
               
               
                   
                 −250 
                 42 
                 42 
                 −250 
                 39 
                 41 
               
               
                   
                 −300 
                 30 
                 27 
                 −300 
                 27 
                 25 
               
               
                   
                 −350 
                 21 
                 19 
                 −350 
                 20 
                 17 
               
               
                   
                 −400 
                 16 
                 14 
                 −400 
                 15 
                 11 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Z = 2 m 
               
             
          
           
               
                   
                 X 
                 LED 
                 Flu. 
                 Y 
                 LED 
                 Flu. 
               
               
                   
                 (cm) 
                 (lux) 
                 (lux) 
                 (cm) 
                 (lux) 
                 (lux) 
               
               
                   
                   
               
             
          
           
               
                   
                 400 
                 17 
                 16 
                 400 
                 16 
                 14 
               
               
                   
                 350 
                 22 
                 22 
                 350 
                 21 
                 20 
               
               
                   
                 300 
                 31 
                 32 
                 300 
                 29 
                 31 
               
               
                   
                 250 
                 47 
                 50 
                 250 
                 44 
                 47 
               
               
                   
                 200 
                 77 
                 81 
                 200 
                 72 
                 73 
               
               
                   
                 150 
                 132 
                 130 
                 150 
                 121 
                 122 
               
               
                   
                 100 
                 214 
                 208 
                 100 
                 207 
                 195 
               
               
                   
                 50 
                 296 
                 296 
                 50 
                 292 
                 281 
               
               
                   
                 0 
                 330 
                 340 
                 0 
                 329 
                 339 
               
               
                   
                 −50 
                 295 
                 294 
                 −50 
                 293 
                 302 
               
               
                   
                 −100 
                 215 
                 209 
                 −100 
                 209 
                 200 
               
               
                   
                 −150 
                 125 
                 127 
                 −150 
                 124 
                 118 
               
               
                   
                 −200 
                 72 
                 77 
                 −200 
                 72 
                 68 
               
               
                   
                 −250 
                 46 
                 50 
                 −250 
                 44 
                 47 
               
               
                   
                 −300 
                 31 
                 33 
                 −300 
                 30 
                 32 
               
               
                   
                 −350 
                 22 
                 22 
                 −350 
                 22 
                 21 
               
               
                   
                 −400 
                 17 
                 16 
                 −400 
                 16 
                 14 
               
               
                   
                   
               
             
          
         
       
     
     Referring to  FIG. 13 , as the side of the ceiling lamp  10  of the present invention is provided with the LED excitation unit  4 , a structural position and an issue of thermal strain degradation resulted from waste heat generated by the excitation unit  4  should be taken into account. Therefore, a single-unit frame  6  is used, wherein an interior of the frame  6  is formed with a slot  67  for installing the excitation unit  4 . The frame  6  is further provided with a fastening lip  64  and a support plate  65  between which the light guide plate  1 , the reflection plate  2  and the light diffuser plate  3  are clamped. In addition, the assembly element  60  can be used for locking, and there are four frames  6  at four sides of the light guide plate  1 , with the frames  6  being assembled with the light guide plate  1  by any corner joint method. On the other hand, the assembly element  60  can assemble and fix with the light guide plate  1 , the reflection plate  2  and the light diffuser plate  3 , wherein a pad  63  can be provided between the assembly element  60  and the reflection plate  2  for buffering, such that the assembly element  60  will not directly press on the reflection plate  2  or the light guide plate  1 . 
     An upper end of the frame  6  is extended with a cooling fin  68 , wherein the cooling fin  68  is set at an upward position to prevent from occupying a horizontal space of the light-weight steel frame  8 . If the horizontal space is sufficient, then the cooling fin  68  can be set as a horizontal shape. To not affect appearance of the light-weight steel frame  8 , the cooling fin  68  can be even set as downward to contact indoor air, so as to acquire a better heat exchange rate. 
     The frame  6  can be made by a metallic material of higher thermal conductivity, such as aluminum alloy. Thermal conductive adhesive can be provided between the slot  67  and the excitation unit  4  for fixing and obtaining a fast directed heat transfer effect. 
     The light-weight steel frame  8  is hooked on an indoor roof with hooks  81 , forming a space in a length of the hook  81 . That space can satisfy the emplacement of the cooling fin  68  and the requirement of the cooling space. 
     The cooling fin  68  which is extended upward above the frame  6  is provided with a height, and a concaved hole is formed above an interior of the ceiling lamp  10 . The concaved hole can provide for the emplacement of the power supply  7 . The electricity provided by the power supply  7  is connected to the LED excitation unit  4  through a circuit, providing a source of operation to the excitation unit  4 . The power supply  7  can be locked by the assembly element  60  at a same time, and can be assembled at the pad  63  through a slab connection method. Therefore, at a same time when locking the assembly element  60 , the installation position of the power supply  7  can be fixed as well. 
     Referring to  FIG. 14  and  FIG. 15 , the light beams is guided by the LED excitation unit  4  into the entrance surface  100  on the side of the light guide plate  1 , followed by filling, traveling and being transformed in the light guide plate  1 . One entrance surface  100  is parallel and symmetric to the opposite entrance surface  100 . Therefore, the excitation unit  4  is also symmetric (as shown in  FIG. 2 ), and the entrance surface  100  of the light guide plate  1  should be at least parallel at two sides or there can be as many as four entrance surfaces  100  at four sides of the light guide plate  1 , with the corresponding excitation units  4 . Basically, for the implementation of the present invention, the entrance surfaces  100  are set as parallel and symmetric that the requirement of illumination on the projection area can be satisfied. 
     Two sets of opposite LED excitation units  4  are implemented on two opposite sides of the light guide plate  1 ; hence, the two light beams B generated are emitted toward each other in a straight line. When the light guide plate  1  is in a rectangular shape and the illumination angle is defined at θ, the illumination beams that are projected will basically form a rectangular frame  91  and a projection area  9  will be driven by the rectangular frame  91  to form an elliptical shape, after being added by the scattering effect. 
     To obtain a more uniform edge shape for the projection area  9 , each side of the light guide plate  1  is implemented with the entrance surface  100  (as shown in  FIG. 15 ), and the multiple light beams B, which emit toward one another, are formed after assembling the corresponding LED excitation units  4 . In addition, according to the defined illumination angle θ, two interleaved rectangular frames  91 ,  92  are formed, resulting in the projection area  9  which is closer to a circle, after being added by the scattering effect. 
     The arrangement of the entrance surface  100  depends upon a number of symmetric sides of the light guide plate  1 . If the light guide plate  1  is a symmetric polygon, then each side is implemented with the entrance surface  100  and the LED excitation unit  4 , and the projection area  9  will be even closer to a circle. 
     It is of course to be understood that the embodiments described herein is merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.