# Patent

## Title
Light guide element for controlling light shape

## Abstract

A light guide element for controlling light shape includes a light-incident surface, a light-emitting surface, a first reflecting surface, and a second reflecting surface. The light-incident surface includes a first outer peripheral edge and a first inner peripheral edge. The light-emitting surface includes a second outer peripheral edge and a second inner peripheral edge. The first reflecting surface is constructed by a first profile curve, and connects the first and the second outer peripheral edge. The first profile curve is a connecting line of two points respectively on the first outer peripheral edge and the second outer peripheral edge. The second reflecting surface is constructed by a second profile curve, and connects the first and the second inner peripheral edge. The second profile curve is a connecting line of two points respectively on the first inner peripheral edge and the second inner peripheral edge.

## Background
RELATED APPLICATIONS
This application claims priority to Taiwan Application Serial Number 102115900, filed May 3, 2013, which is herein incorporated by reference.
BACKGROUND
1. Field of the Invention
The present invention relates to a light guide element, and more particularly to a light guide element for controlling a light shape.
2. Description of Related Art
A conventional lamp consists essentially of a bulb and a reflecting mask. The reflecting mask mainly functions to guide light generated from the bulb to a required direction and to change light shapes generated while the bulb irradiates. However, the light shapes varied through the reflecting mask have limited diversities, and are usually a light-concentrating type, thus having limited applicability of the lamp.
Another conventional lamp can change a light shape generated from a light source by collaborating with a secondary optical element. However, in this structure, a recess has to be disposed in a center of the optical element to receive the light source for achieving the object of light shape adjustment. Thus, the secondary optical element has to match with different types or quantities of light sources to change the whole structure design, thus resulting in cost increase.
Hence, a light guide element is needed to overcome the foregoing problems.
SUMMARY
One aspect of the present invention is to provide a light guide element for controlling a light shape by using a total reflection characteristic of a light beam to change a travel direction of the light beam, thus achieving an object of adjusting the light form emitted from the light guide element. Therefore, applications of the light guide element may meet irradiation requirements of various light beam angles, and also reduce power consumption.
Another aspect of the present invention is to provide a light guide element for controlling a light shape by using profile curves to change curved surface shapes of a first reflecting surface, a second reflecting surface and a light-emitting surface, thereby adjusting a travel direction of a light beam in the light guide element to achieve an object of adjusting the light form emitted from the light guide element.
Another aspect of the present invention is to provide a light guide element for controlling a light shape by using a Bezier curve function to define respective profile curves, thus not only simplifying definition rules of respective curved surfaces but also controlling an overall profile shape of the light guide element in an intuitive manner.
According to the aforementioned objects, the present invention provides a light guide element for controlling a light shape. The light guide element is suitable for guiding at least one light beam, in which the at least one light beam is totally reflected in the light guide element to generate a predetermined light beam angle. The light guide element is an annular frustum and includes a light-incident surface, a light-emitting surface, a first reflecting surface and a second reflecting surface. The light-incident surface has a first outer peripheral edge and a first inner peripheral edge. The light-emitting surface is opposite to the light-incident surface and has a second outer peripheral edge and a second inner peripheral edge. The first reflecting surface connects the first outer peripheral edge and the second outer peripheral edge, in which the first reflecting surface is a curved surface constructed by a first profile curve. The first profile curve is a connecting line from a first initial point on the first outer peripheral edge to a first terminating point on the second outer peripheral edge. The second reflecting surface connects the first inner peripheral edge and the second inner peripheral edge, in which the second reflecting surface is a curved surface constructed by a second profile curve. The second profile curve is a connecting line from a second initial point on the first inner peripheral edge to a second terminating point on the second inner peripheral edge.
According to an embodiment of the present invention, the first profile curve is defined by a Bezier curve function,




  
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There is at least one first control point between the first initial point and the first terminating point. “Pi” represents a position coordinate of an ith point in the Bezier curve function, in which when a total number of at least one first control point is one, a position coordinate of the first initial point is (X0,Y0), a position coordinate of the first control point is (X1,Y1) and a position coordinate of the first terminating point is (X2,Y2). “n” represents the total number of the at least one first control point plus 1. “Wi” represents a weight of the ith point. “t” represents a ratio of a length between a predetermined point and the first initial point to a total length of the first profile curve. Constraints of the first profile curve are:



  
    
      
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α1 represents an angle included between a horizontal line and a connecting line from the first initial point to the at least one first control point α2 represents an angle included between a horizontal line and a connecting line from the first initial point to the first terminating point. θ1 represents a refracting angle of the at least one light beam entering from outside of the light guide element. θ2 represents an incident angle of the at least one light beam which is incident toward the first reflecting surface after entering the light guide element. nmaterial represents a refractive index of the light guide element.
According to another embodiment of the present invention, the second profile curve is defined by a Bezier curve function,




  
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There is at least one second control point between the second initial point and the second terminating point. “Pi” represents a position coordinate of an ith point in the Bezier curve function, in which when a total number of at least one second control point is one, a position coordinate of the second initial point is (X′0,Y′0), a position coordinate of the second control point is (X′1,Y′1) and a position coordinate of the second terminating point is (X′2,Y′2). “n” represents the total number of the at least one second control point plus 1. “Wi” represents a weight of the ith point. “t” represents a ratio of a length between a predetermined point and the second initial point to a total length of the second profile curve. Constraints of the second profile curve are:



  
    
      
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α1′ represents an angle included between a horizontal line and a connecting line from the second initial point to the at least one second control point. α2′ represents an angle included between a horizontal line and a connecting line from the second initial point to the second terminating point. θ1′ represents a refracting angle of the at least one light beam entering from outside of the light guide element. θ2′ represents an incident angle of the at least one light beam which is incident toward the second reflecting surface after entering the light guide element. nmaterial represents a refractive index of the light guide element.
According to another embodiment of the present invention, the first profile curve and the second profile curve have the same profile or different profiles.
According to another embodiment of the present invention, the light-emitting surface is defined by a third profile curve, in which the third profile curve is a connecting line from a third initial point on the second outer peripheral edge to a third terminating point on the second inner peripheral edge.
According to another embodiment of the present invention, the third profile curve is defined by a Bezier curve function,




  
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There is at least one third control point between the third initial point and the third terminating point. “Pi” represents a position coordinate of an ith point in the Bezier curve function, in which when a total number of at least one third control point is one, a position coordinate of the third initial point is (X3,Y3), a position coordinate of the third control point is (X4,Y4) and a position coordinate of the third terminating point is (X5,Y5). “n” represents the total number of the at least one third control point plus 1. “Wi” represents a weight of the ith point. “t” represents a ratio of a length between a predetermined point and the third initial point to a total length of the third profile curve. Constraints of the second profile curve are: X3=X5; Y3≧Y4≧Y5; and 0≦Wi≦1.
According to another embodiment of the present invention, the first reflecting surface is formed from a plurality of first reflecting curved surfaces, in which each of the first reflecting curved surfaces is constructed by the first profile curve.
According to another embodiment of the present invention, the second reflecting surface is formed from a plurality of second reflecting curved surfaces, in which each of the second reflecting curved surfaces is constructed by the second profile curve.
According to the aforementioned objects, the present invention provides a lamp. The lamp includes a light guide element and a light source. The light guide element is an annular frustum and includes a light-incident surface, a light-emitting, a first reflecting surface and a second reflecting surface. The light-incident surface has a first outer peripheral edge and a first inner peripheral edge. The light-emitting surface is opposite to the light-incident surface and has a second outer peripheral edge and a second inner peripheral edge. The first reflecting surface connects the first outer peripheral edge and the second outer peripheral edge, in which the first reflecting surface is a curved surface constructed by a first profile curve. The first profile curve is a connecting line from a first initial point on the first outer peripheral edge to a first terminating point on the second outer peripheral edge. The second reflecting surface connects the first inner peripheral edge and the second inner peripheral edge, in which the second reflecting surface is a curved surface constructed by a second profile curve. The second profile curve is a connecting line from a second initial point on the first inner peripheral edge to a second terminating point on the second inner peripheral edge. A light generated from the light source enters the light guide element from the light-incident surface and emits out of the light-emitting surface to generate a predetermined light beam angle of the light.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:
FIG. 1A is a schematic structural diagram showing a light guide element in accordance with a first embodiment of the present invention;
FIG. 1B is a schematic cross-sectional view of the light guide element viewed along a line A-A in FIG. 1A;
FIG. 2A is a schematic structural diagram showing a light guide element in accordance with a second embodiment of the present invention;
FIG. 2B is a schematic cross-sectional view of the light guide element viewed along a line B-B in FIG. 2A;
FIG. 2C is a schematic diagram of a first profile curve in accordance with the second embodiment of the present invention;
FIG. 2D is a candlepower distribution curve generated from the light guide element in accordance with the second embodiment of the present invention;
FIG. 3A is a schematic structural diagram showing a light guide element in accordance with a third embodiment of the present invention;
FIG. 3B is a schematic cross-sectional view of the light guide element viewed along a line C-C in FIG. 3A;
FIG. 3C is a schematic diagram of a first profile curve in accordance with the third embodiment of the present invention;
FIG. 3D is a candlepower distribution curve generated from the light guide element in accordance with the third embodiment of the present invention;
FIG. 4A is a schematic structural diagram showing a light guide element in accordance with a fourth embodiment of the present invention;
FIG. 4B is a schematic cross-sectional view of the light guide element viewed along a line D-D in FIG. 4A;
FIG. 4C is a schematic diagram of a first profile curve in accordance with the fourth embodiment of the present invention;
FIG. 4D is a candlepower distribution curve generated from the light guide element in accordance with the fourth embodiment of the present invention;
FIG. 5A is a schematic structural diagram showing a light guide element in accordance with a fifth embodiment of the present invention;
FIG. 5B is a schematic cross-sectional view of the light guide element viewed along a line E-E of FIG. 5A;
FIG. 5C is a schematic diagram of a first profile curve in accordance with the fifth embodiment of the present invention;
FIG. 5D is a candlepower distribution curve generated from the light guide element in accordance with the fifth embodiment of the present invention;
FIG. 6A is a schematic structural diagram showing a light guide element in accordance with a first example of a sixth embodiment of the present invention;
FIG. 6B is a candlepower distribution curve generated from the light guide element in accordance with the first example of the sixth embodiment of the present invention;
FIG. 7A is a schematic structural diagram showing a light guide element in accordance with a second example of the sixth embodiment of the present invention;
FIG. 7B is a candlepower distribution curve generated from the light guide element in accordance with the second example of the sixth embodiment of the present invention;
FIG. 8A is a schematic structural diagram showing a light guide element in accordance with a third example of the sixth embodiment of the present invention;
FIG. 8B is a candlepower distribution curve generated from the light guide element in accordance with the third example of the sixth embodiment of the present invention;
FIG. 9A is a schematic structural diagram showing a light guide element in accordance with a fourth example of the sixth embodiment of the present invention;
FIG. 9B is a candlepower distribution curve generated from the light guide element in accordance with the fourth example of the sixth embodiment of the present invention;
FIG. 10A is a schematic structural diagram showing a light guide element in accordance with a fifth example of the sixth embodiment of the present invention; and
FIG. 10B is a candlepower distribution curve generated from the light guide element in accordance with the fifth example of the sixth embodiment of the present invention.



DETAILED DESCRIPTION
Referring to FIGS. 1A and 1B, FIG. 1A is a schematic structural diagram of a light guide element 100 in accordance with a first embodiment, and FIG. 1B is a schematic cross-sectional view of the light guide element 100 viewed along a line A-A in FIG. 1A. In the present embodiment, the light guide element 100 is suitable for use in guiding a light beam and enabling the light beam to be totally reflected in the light guide element 100, so as to generate different light beam angles. In the present embodiment, the light beam may come from a light source, such as a light emitting diode (LED). The light guide element 100 is an annular frustum having a through hole 110. The light guide element 100 includes a light-incident surface 112, a light-emitting surface 114, a first reflecting surface 116 and a second reflecting surface 118. The through hole 110 forms a first opening 110a on the light-incident surface 112, and the light-incident surface 112 has a first outer peripheral edge 112a and a first inner peripheral edge 112b. The light-emitting surface 114 is opposite to the light-incident surface 112. The through hole 110 forms a second opening 110b on the light-emitting surface 114, and the light-emitting surface 114 has a second outer peripheral edge 114a and a second inner peripheral edge 114b. 
The first reflecting surface 116 connects the first outer peripheral edge 112a and the second outer peripheral edge 114a, and the first reflecting surface 116 is a curved surface constructed by a first profile curve B1. The first profile curve B1 is a connecting line from a first initial point on the first outer peripheral edge 112a to a first terminating point on the second outer peripheral edge 114a. It is noted that the first profile curve B1 in the present embodiment is a curve of intersection between the first reflecting surface 116 and any cut plane which is perpendicular to the light-incident surface 112 and passes through a center of the light guide element 100. The second reflecting surface 118 connects the first inner peripheral edge 112b and the second inner peripheral edge 114b, and the second reflecting surface 118 is a curved surface constructed by a second profile curve B2. The second profile curve B2 is a connecting line from a second initial point on the first inner peripheral edge 112b to a second terminating point on the second inner peripheral edge 114b. Similarly, the second profile curve B2 in the present embodiment is a curve of intersection between the second reflecting surface 118 and any cut plane which is perpendicular to the light-incident surface 112 and passes through the center of the light guide element 100.
In one embodiment, the first profile curve B1 is defined by a Bezier curve function. Bezier curves are various curves illustrated mainly by using three or more points of position coordinates with different weights according to the Bezier curve function. The Bezier curve function is shown as




  
    
      
        
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where “Pi” represents a position coordinate of an ith point in the Bezier curve function. In the present embodiment, there is at least one first control point between the first initial point and the first terminating point. For example, when a total number of the at least one first control point is one, the first control point P1 is located between the first initial point P0 and the first terminating point P2. The position of the first control point is mainly used for determining a radian of the first profile curve B1. For example, when a total number of the at least one first control point is one, a position coordinate of the first initial point P0 is (X0,Y0), a position coordinate of the first control point P1 is (X1,Y1), and a position coordinate of the first terminating point P2 is (X2,Y2). In the Bezier curve function, “n” represents the total number of the at least one first control point plus 1, and “Wi” represents a weight of a point Pi. For example, when the total number of the at least one first control point is 2, “n” is 3. In addition, “W1” represents a weight of the first control point P1 which can adjust the shape of the first profile curve B1. As shown in FIG. 1B, the weight W1 in a connecting line from the first initial point P0 to the first control point P1 is defined as 1, and the weight W1 in a connecting line from the first initial point P0 to the first terminating point P2 is defined as 0. If the weight of the first control point P1 approaches 1, the first profile curve B1 will trend to the connecting line from the first initial point P0 to the first control point P1. Similarly, if the weight of the first control point P1 approaches 0, the first profile curve B1 will trend to the connecting line from the first initial point P0 to the first terminating point P2. In the Bezier curve function, “t” represents a ratio of a length between a predetermined point and the first initial point to a total length of the first profile curve B1. The aforementioned “total length” is a length of the connecting line from the first initial point to the first terminating point. Therefore, “t” may represent a corresponding value of a position of any point on the first profile curve B1 between the first initial point and the first terminating point.
After the first initial point P0, the first control point P1 and the first terminating point P2 are defined, the first profile curve B1 are further defined by constraints shown as:




  
    
      
        
          
            
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Referring to FIG. 1B again, α1 represents an angle included between a horizontal line and the connecting line from the first initial point P0 to the first control point P1. α2 represents an angle included between a horizontal line and the connecting line from the first initial point P0 to the first terminating point P2. θ1 represents a refracting angle of the light beam entering from outside of the light guide element 100. θ2 represents an incident angle of the light beam which is incident toward the first reflecting surface 116 after entering the light guide element 100. nmaterial represents a refractive index of the light guide element 100. Therefore, adjusting each parameter value of the constraints may change the shape of the first reflecting surface 116.
Referring to FIGS. 1A and 1B again, in one embodiment, the second profile curve B2 may be the same curve as the first profile curve B1. Both the first profile curve B1 and the second profile curve B2 are defined by the aforementioned Bezier curve function. For clarity of explanation, P′i, X′i, and Y′i, are used below to represent Pi, Xi and Yi in equations (1) and (2).
In the present embodiment, there is at least one second control point between the second initial point and the second terminating point. For example, when a total number of the at least one first control point is one, the second control point P′1 is located between the second initial point P′0 and the second terminating point P′2. The position of the second control point is mainly used for determining a radian of the second profile curve B2. For example, when a total number of the at least one second control point is one, a position coordinate of the second initial point P′0 is (X′0,Y′0), a position coordinate of the second control point P′1 is (X′1,Y′1), and a position coordinate of the second terminating point P′2 is (X′2,Y′2). In the Bezier curve function, “n” represents the total number of the at least one second control point plus 1. In addition, “Wi” represents a weight of the second control point P′i which can adjust the shape of the second profile curve B2. As shown in FIG. 1B, the weight W1 in a connecting line from the second initial point P′0 to the second control point P′1 is defined as 1, and the weight W1 in a connecting line from the second initial point P′0 to the second terminating point P′2 is defined as 0. If the weight of the second control point P′1 approaches 1, the second profile curve B2 will trend to the connecting line from the second initial point P′0 to the second control point P′1. Similarly, if the weight of the second control point P′1 approaches 0, the second profile curve B2 will trend to the connecting line from the second initial point P′0 to the second terminating point P′2. In the Bezier curve function, “t” represents a ratio of a length between a predetermined point and the second initial point to a total length of the second profile curve B2. The aforementioned “total length” is a length of the connecting line from the second initial point to the second terminating point. Therefore, “t” may represent a corresponding value of a position of any point on the second profile curve B2 between the second initial point and the second terminating point.
After the second initial point P′0, the second control point P′1 and the second terminating point P′2, are defined, the second profile curve B2 are further defined by constraints shown as:




  
    
      
        
          
            
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          ;
        
        ⁢
        
          

        
        ⁢
        
          
            
              90
              ⁢
              °
            
            ≧
            
              α
              1
              ′
            
            ≧
            
              α
              2
              ′
            
          
          ;
        
        ⁢
        
          

        
        ⁢
        
          
            
              0
              ≦
              
                α
                1
                ′
              
            
            =
            
              
                θ
                1
                ′
              
              +
              
                θ
                2
                ′
              
              -
              
                90
                ⁢
                °
              
            
          
          ;
        
        ⁢
        
          

        
        ⁢
        
          
            
              θ
              1
              ′
            
            =
            
              
                sin
                
                  -
                  1
                
              
              ⁡
              
                (
                
                  1
                  
                    n
                    material
                  
                
                )
              
            
          
          ;
        
        ⁢
        
          

        
        ⁢
        
          
            
              θ
              2
              ′
            
            ≧
            
              
                90
                ⁢
                °
              
              -
              
                θ
                1
                ′
              
            
          
          ;
          and
        
        ⁢
        
          

        
        ⁢
        
          0
          ≦
          
            W
            i
          
          ≦
          1.
        
      
    
    
      
        (
        3
        )
      
    
  




Referring to FIG. 1B again, α1′ represents an angle included between a horizontal line and the connecting line from the second initial point P0′ to the first control point P′1. α2′ represents an angle included between a horizontal line and the connecting line from the second initial point P′0 to the second terminating point P′2. θ1′ represents a refracting angle of the light beam entering from outside of the light guide element 100. θ2′ represents an incident angle of the light beam which is incident toward the second reflecting surface 118 after entering the light guide element 100. nmaterial represents a refractive index of the light guide element 100. Therefore, adjusting each parameter value of the constraints may change the shape of the second reflecting surface 118.
It can be known from the above descriptions that, the second profile curve B2 is defined by the same Bezier curve function and the same constraints for the first profile curve B1. Therefore, in one embodiment, the second profile curve B2 and the first profile curve B1 can have the same profile, so that the second reflecting surface 118 and the first reflecting surface 116 are symmetrical. However, in another embodiment, the second profile curve B2 and the first profile curve B1 may have different profiles defined by different parameter values, so that the second reflecting surface 118 and the first reflecting surface 116 are not symmetrical.
Referring to FIG. 2A to FIG. 2D, FIG. 2A is a schematic structural diagram a light guide element 200 in accordance with a second embodiment of the present invention; FIG. 2B is a schematic cross-sectional view of the light guide element 200 viewed along a line B-B in FIG. 2A; FIG. 2C is a schematic diagram of a first profile curve in accordance with the second embodiment of the present invention; and FIG. 2D is a candlepower distribution curve generated from the light guide element in accordance with the second embodiment of the present invention.
In the second embodiment, as shown in FIG. 2C, the first profile curve B1 of the light guide element 200 is formed from the parameter values which are P0=(0,0), P1=(21.3,13), P2=(36,8.5) and W1=0.45. The second profile curve B2 and the first profile curve B1 are symmetrical. As shown in FIG. 2B, the light beam enters the light guide element 200 from a light-incident surface 212, and is reflected out of the light-emitting surface 214 by the light guide element 200. In the present embodiment, the light beam is emitted from the light guide element 200 at a light beam angle of about 82 degrees.
Referring to FIG. 3A to FIG. 3D, FIG. 3A is a schematic structural diagram of a light guide element 300 in accordance with a third embodiment of the present invention; FIG. 3B is a schematic cross-sectional view of the light guide element 300 viewed along a line C-C in FIG. 3A; FIG. 3C is a schematic diagram of a first profile curve in accordance with the third embodiment of the present invention; and FIG. 3D is a candlepower distribution curve generated from the light guide element in accordance with the third embodiment of the present invention.
In the third embodiment, as shown in FIG. 3C, the first profile curve B1 of the light guide element 300 is formed from the parameter values which are P0=(0,0), P1=(7.6,4.6), P2=(36,8.5) and W1=0.45. The second profile curve B2 and the first profile curve B1 are symmetrical. As shown in FIG. 3B, the light beam enters the light guide element 300 from a light-incident surface 312, and is reflected out of the light-emitting surface 314 by the light guide element 300. In the present embodiment, the light beam is emitted from the light guide element 300 at a light beam angle of about 24 degrees.
Referring to FIG. 4A to FIG. 4D, FIG. 4A is a schematic structural diagram of a light guide element 400 in accordance with a fourth embodiment of the present invention; FIG. 4B is a schematic cross-sectional view of the light guide element 400 viewed along a line D-D in FIG. 4A; FIG. 4C is a schematic diagram of a first profile curve in accordance with the fourth embodiment of the present invention; and FIG. 4D is a candlepower distribution curve generated from the light guide element in accordance with the fourth embodiment of the present invention.
In the fourth embodiment, as shown in FIG. 4C, the first profile curve B1 of the light guide element 400 is formed from the parameter values which are P0=(0,0), P1=(24.6,17.2), P2=(36,8.5) and W1=0.45. The second profile curve B2 and the first profile curve B1 are symmetrical. As shown in FIG. 4B, the light beam enters the light guide element 400 from a light-incident surface 412, and is reflected out of the light-emitting surface 414 by the light guide element 400. In the present embodiment, the light beam is emitted from the light guide element 400 at a light beam angle of about 93 degrees.
Referring to FIG. 5A to FIG. 5D, FIG. 5A is a schematic structural diagram of a light guide element 500 in accordance with a fifth embodiment of the present invention; FIG. 5B is a schematic cross-sectional view of the light guide element 500 viewed along a line E-E in FIG. 5A; FIG. SC is a schematic diagram of a first profile curve in accordance with the fifth embodiment of the present invention; and FIG. 5D is a candlepower distribution curve generated from the light guide element in accordance with the fifth embodiment of the present invention.
In the fifth embodiment, the light guide element 500 is similar to the light guide element 100. The light guide element 500 includes a light-incident surface 512, a light-emitting surface 514, a first reflecting surface 516 and a second reflecting surface 518. The first reflecting surface 516 and the second reflecting surface 518 are similar to the first reflecting surface 116 and the second reflecting surface 118. The first reflecting surface 516 and the second reflecting surface 518 are constructed by the same first profile curve B1 and the same second profile curve B2 which are described before, and will not be repeated herein. In the present embodiment, the light-emitting surface 514 has an outer peripheral edge 514a and an inner peripheral edge 514b. The light-emitting surface 514 is constructed by a third profile curve B3. The third profile curve B3 is a connecting line from a third initial point on the outer peripheral edge 514a to a third terminating point on the inner peripheral edge 514b. 
It is noted that the third profile curve B3 in the present embodiment is a curve of intersection between the light-emitting surface 514 and any cut plane which is perpendicular to the light-incident surface 512 and passes through a center of the light guide element 500. In one embodiment, the third profile curve B3 and the first profile curve B1 may be defined by the same profile curve. Both the first profile curve B1 and the third profile curve B3 are defined by the aforementioned Bezier curve function.
In the present embodiment, there is at least one third control point between the third initial point and the third terminating point. For example, when a total number of the at least one third control point is one, the third control point P4 is located between the third initial point P3 and the third terminating point P5. The position of the third control point is mainly used for determining a radian of the third profile curve B3. For example, when a total number of the at least one third control point is one, a position coordinate of the third initial point P3 is (X3,Y3), a position coordinate of the third control point P4 is (X4,Y4), and a position coordinate of the third terminating point P5 is (X5,Y5). In the Bezier curve function, the definition of “Pi”, “n”, “Wi” and “t” are described in the above descriptions, and will not be described again. After the third initial point P3, the third control point P4 and the third terminating point P5 are defined, the third profile curve B3 are further defined by constraints shown as X3=X5; Y3≧Y4≧Y5; and 0≦Wi≦1.
Referring to FIG. 5A to FIG. 5D again, in the fifth embodiment, the first profile curve B1 and the second profile curve B2 are formed from the same parameter values of the third embodiment, i.e. P0=(0,0), P1=(7.6,4.6), P2=(36,8.5) and W1=0.45. As shown in FIG. 5C, the third profile curve B3 of the light guide element 500 is formed from the parameter values which are P3=(0,21), P4=(10.6,10.6), P5=(0,0) and W4=0.45. As shown in FIG. 5B, the light beam enters the light guide element 500 from a light-incident surface 512, and is reflected out of the light-emitting surface 514 by the light guide element 500. In the present embodiment, the light beam is emitted from the light guide element 500 at a light beam angle of about 13 degrees. Therefore, from the first embodiment to the fifth embodiment above, adjusting each parameter value of the constraints may change the shape of the light-emitting surface 514.
Referring to FIG. 6A and FIG. 6B, FIG. 6A is a schematic structural diagram a light guide element 600 in accordance with a first example of a sixth embodiment of the present invention; and FIG. 6B is a candlepower distribution curve generated from the light guide element 600 in accordance with the first example of the sixth embodiment of the present invention. In the present embodiment, the light guide element 600 includes a light-incident surface 612, a light-emitting surface 614, a first reflecting surface 616 and a second reflecting surface 618. The first reflecting surface 616 is formed from six first reflecting curved surfaces. Each of these first reflecting curved surfaces is constructed by the first profile curve B1. Similarly, the second reflecting surface 618 is formed from six second reflecting curved surfaces. Each of these second reflecting curved surfaces is constructed by the second profile curve B2.
Referring to FIG. 7A and FIG. 7B, FIG. 7A is a schematic structural diagram a light guide element 700 in accordance with a second example of the sixth embodiment of the present invention; and FIG. 7B is a candlepower distribution curve generated from the light guide element 700 in accordance with the second example of the sixth embodiment of the present invention. In the present embodiment, the light guide element 700 includes a light-incident surface 712, a light-emitting surface 714, a first reflecting surface 716 and a second reflecting surface 718. The first reflecting surface 716 is formed from eight first reflecting curved surfaces. Each of these first reflecting curved surfaces is constructed by the first profile curve B1. Similarly, the second reflecting surface 618 is formed from eight second reflecting curved surfaces. Each of these second reflecting curved surfaces is constructed by the second profile curve B2.
Referring to FIG. 8A and FIG. 8B, FIG. 8A is a schematic structural diagram of a light guide element 800 in accordance with a third example of the sixth embodiment of the present invention; and FIG. 8B is a candlepower distribution curve generated from the light guide element 800 in accordance with the third example of the sixth embodiment of the present invention. In the present embodiment, the light guide element 800 includes a light-incident surface 812, a light-emitting surface 814, a first reflecting surface 816 and a second reflecting surface 818. The first reflecting surface 816 is formed from twelve first reflecting curved surfaces. Each of these first reflecting curved surfaces is constructed by the first profile curve B1. Similarly, the second reflecting surface 618 is formed from twelve second reflecting curved surfaces. Each of these second reflecting curved surfaces is constructed by the second profile curve B2.
From the above, different shapes of the light guide elements, such as light guide element 600,700 and 800 may form different light beam angles. It is noted that the number of the first reflecting curved surfaces and the second reflecting curved surfaces are described the same, it is possible to utilize different number of the first reflecting curved surfaces and the second reflecting curved surfaces. Additionally, the first profile curve B1 and the second profile curve B2 may be defined by the same profile curve or different profile curves. The following examples are directed to other modifications of the light guide element 600 of the sixth embodiment.
Referring to FIG. 9A and FIG. 9B, FIG. 9A is a schematic structural diagram of a light guide element 600a in accordance with a fourth example of the sixth embodiment of the present invention; and FIG. 9B is a candlepower distribution curve generated from the light guide element 600a in accordance with the fourth example of the sixth embodiment of the present invention. In the present embodiment, the first profile curve B1 of the light guide element 600a is formed from the parameter values which are P0=(0,0), P1=(10.3,6.2), P2=(36,8.5) and W1=0.45. The second profile curve B2 and the first profile curve B1 are symmetrical. In the present embodiment, the light beam is emitted from the light guide element 600a at a light beam angle of about 47 degrees.
Referring to FIG. 10A and FIG. 10B, FIG. 10A is a schematic structural diagram of a light guide element 600b in accordance with a fifth example of the sixth embodiment of the present invention; and FIG. 10B is a candlepower distribution curve generated from the light guide element 600b in accordance with the fifth example of the sixth embodiment of the present invention. In the present embodiment, the first profile curve B1 of the light guide element 600b is formed from the parameter values which are P0=(0,0), P1=(32.8,22.9), P2=(36,8.5) and W1=0.45. The second profile curve B2 is formed from the parameter values which are P′0=(0,0), P′1=(10,15), P′2=(36,8.5) and W1=0. In the present embodiment, the light beam is emitted from the light guide element 600b at a light beam angle of about 63 degrees.
According to the aforementioned embodiments of the present invention, one advantage of the present invention is using profile curves to change curved surface shapes of a first reflecting surface, a second reflecting surface and a light-emitting surface of a light guide element, thereby adjusting a travel direction of the light beam in the light guide element to achieve an object of adjusting the light form emitted from the light guide element. Furthermore, by using a total reflection characteristic of the light beam to change a travel direction of the light beam can achieve an object of adjusting the light form emitted from the light guide element. Therefore, the applications of the light guide element may meet irradiation requirements of various light beam angles, and also reduce power consumption. Additionally, using the Bezier curve function to define respective profile curves can not only simplify definition rules of respective curved surfaces but also can control an overall profile shape of the light guide element in an intuitive manner.
Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.

## Claims

1. A light guide element for controlling a light shape, suitable for guiding at least one light beam, wherein the at least one light beam is totally reflected in the light guide element to generate a predetermined light beam angle, and the light guide element is an annular frustum and comprises:
a light-incident surface having a first outer peripheral edge and a first inner peripheral edge;
a light-emitting surface which is opposite to the light-incident surface and has a second outer peripheral edge and a second inner peripheral edge;
a first reflecting surface connecting the first outer peripheral edge and the second outer peripheral edge, wherein the first reflecting surface is a curved surface constructed by a first profile curve, wherein the first profile curve is a connecting line from a first initial point on the first outer peripheral edge to a first terminating point on the second outer peripheral edge; and
a second reflecting surface connecting the first inner peripheral edge and the second inner peripheral edge, wherein the second reflecting surface is a curved surface constructed by a second profile curve, wherein the second profile curve is a connecting line from a second initial point on the first inner peripheral edge to a second terminating point on the second inner peripheral edge.

2. The light guide element of claim 1, wherein the first profile curve is defined by a Bezier curve function,




  
    
      B
      ⁡
      
        (
        t
        )
      
    
    =
    
      
        
          ∑
          
            i
            =
            0
          
          n
        
        ⁢
        
          
            (
            
              
                
                  n
                
              
              
                
                  i
                
              
            
            )
          
          ⁢
          
            
              
                t
                i
              
              ⁡
              
                (
                
                  1
                  -
                  t
                
                )
              
            
            
              n
              -
              i
            
          
          ⁢
          
            P
            i
          
          ⁢
          
            W
            i
          
        
      
      
        
          ∑
          
            i
            =
            0
          
          n
        
        ⁢
        
          
            (
            
              
                
                  n
                
              
              
                
                  i
                
              
            
            )
          
          ⁢
          
            
              
                t
                i
              
              ⁡
              
                (
                
                  1
                  -
                  t
                
                )
              
            
            
              n
              -
              i
            
          
          ⁢
          
            W
            i
          
        
      
    
  
  ;



there is at least one first control point between the first initial point and the first terminating point; Pi represents a position coordinate of an ith point in the Bezier curve function; when a total number of at least one first control point is one, a position coordinate of the first initial point is (X0,Y0); a position coordinate of the first control point is (X1,Y1); and a position coordinate of the first terminating point is (X2,Y2);
wherein n represents the total number of the at least one first control point plus 1; Wi represents a weight of the ith point; and t represents a ratio of a length between a predetermined point and the first initial point to a total length of the first profile curve;
wherein constraints of the first profile curve are




  
    
      
        X
        0
      
      ≦
      
        X
        1
      
      ≦
      
        X
        2
      
    
    ;
  




  
    
      
        90
        ⁢
        °
      
      ≧
      
        α
        1
      
      ≧
      
        α
        2
      
    
    ;
  




  
    
      
        0
        ≦
        
          α
          1
        
      
      =
      
        
          θ
          1
        
        +
        
          θ
          2
        
        -
        
          90
          ⁢
          °
        
      
    
    ;
  




  
    
      
        θ
        1
      
      =
      
        
          sin
          
            -
            1
          
        
        ⁡
        
          (
          
            1
            
              n
              material
            
          
          )
        
      
    
    ;
  




  
    
      
        θ
        2
      
      ≧
      
        
          90
          ⁢
          °
        
        -
        
          θ
          1
        
      
    
    ;
    and
  




  
    
      0
      ≦
      
        W
        i
      
      ≦
      1
    
    ;
  


wherein α1 represents an angle included between a horizontal line and a connecting line from the first initial point to the at least one first control point; α2 represents an angle included between a horizontal line and a connecting line from the first initial point to the first terminating point, θ1 represents a refracting angle of the at least one light beam entering from outside of the light guide element; θ2 represents an incident angle of the at least one light beam which is incident toward the first reflecting surface after entering the light guide element, and nmaterial represents a refractive index of the light guide element.

3. The light guide element of claim 1, wherein the second profile curve is defined by a Bezier curve function,




  
    
      B
      ⁡
      
        (
        t
        )
      
    
    =
    
      
        
          ∑
          
            i
            =
            0
          
          n
        
        ⁢
        
          
            (
            
              
                
                  n
                
              
              
                
                  i
                
              
            
            )
          
          ⁢
          
            
              
                t
                i
              
              ⁡
              
                (
                
                  1
                  -
                  t
                
                )
              
            
            
              n
              -
              i
            
          
          ⁢
          
            P
            i
          
          ⁢
          
            W
            i
          
        
      
      
        
          ∑
          
            i
            =
            0
          
          n
        
        ⁢
        
          
            (
            
              
                
                  n
                
              
              
                
                  i
                
              
            
            )
          
          ⁢
          
            
              
                t
                i
              
              ⁡
              
                (
                
                  1
                  -
                  t
                
                )
              
            
            
              n
              -
              i
            
          
          ⁢
          
            W
            i
          
        
      
    
  
  ;



there is at least one second control point between the second initial point and the second terminating point; Pi represents a position coordinate of an ith point in the Bezier curve function; when a total number of at least one second control point is one, a position coordinate of the second initial point is (X′0,Y′0); a position coordinate of the at least one second control point is (X′1,Y′1); and a position coordinate of the second terminating point is (X′2,Y′2);
wherein n represents the total number of the at least one second control point plus 1, Wi represents a weight of the ith point; and t represents a ratio of a length between a predetermined point and the second initial point to a total length of the second profile curve;
wherein constraints of the second profile curve are




  
    
      
        X
        0
        ′
      
      ≦
      
        X
        1
        ′
      
      ≦
      
        X
        2
        ′
      
    
    ;
  




  
    
      
        90
        ⁢
        °
      
      ≧
      
        α
        1
        ′
      
      ≧
      
        α
        2
        ′
      
    
    ;
  




  
    
      
        0
        ≦
        
          α
          1
          ′
        
      
      =
      
        
          θ
          1
          ′
        
        +
        
          θ
          2
          ′
        
        -
        
          90
          ⁢
          °
        
      
    
    ;
  




  
    
      
        θ
        1
        ′
      
      =
      
        
          sin
          
            -
            1
          
        
        ⁡
        
          (
          
            1
            
              n
              material
            
          
          )
        
      
    
    ;
  




  
    
      
        θ
        2
        ′
      
      ≧
      
        
          90
          ⁢
          °
        
        -
        
          θ
          1
          ′
        
      
    
    ;
    and
  




  
    
      0
      ≦
      
        W
        i
      
      ≦
      1
    
    ;
  


wherein α1′ represents an angle included between a horizontal line and a connecting line from the second initial point to the at least one second control point; α2′ represents an angle included between a horizontal line and a connecting line from the second initial point to the second terminating point, θ1′ represents a refracting angle of the at least one light beam entering from outside of the light guide element; θ2′ represents an incident angle of the at least one light beam which is incident toward the second reflecting surface after entering the light guide element, and nmaterial represents a refractive index of the light guide element.

4. The light guide element of claim 1, wherein the first profile curve and the second profile curve have the same profile or different profiles.

5. The light guide element of claim 1, wherein the light-emitting surface is defined by a third profile curve, wherein the third profile curve is a connecting line from a third initial point on the second outer peripheral edge to a third terminating point on the second inner peripheral edge.

6. The light guide element of claim 5, wherein the third profile curve is defined by a Bezier curve function,




  
    
      B
      ⁡
      
        (
        t
        )
      
    
    =
    
      
        
          ∑
          
            i
            =
            0
          
          n
        
        ⁢
        
          
            (
            
              
                
                  n
                
              
              
                
                  i
                
              
            
            )
          
          ⁢
          
            
              
                t
                i
              
              ⁡
              
                (
                
                  1
                  -
                  t
                
                )
              
            
            
              n
              -
              i
            
          
          ⁢
          
            P
            i
          
          ⁢
          
            W
            i
          
        
      
      
        
          ∑
          
            i
            =
            0
          
          n
        
        ⁢
        
          
            (
            
              
                
                  n
                
              
              
                
                  i
                
              
            
            )
          
          ⁢
          
            
              
                t
                i
              
              ⁡
              
                (
                
                  1
                  -
                  t
                
                )
              
            
            
              n
              -
              i
            
          
          ⁢
          
            W
            i
          
        
      
    
  
  ;



there is at least one third control point between the third initial point and the third terminating point, wherein Pi represents a position coordinate of an ith point in the Bezier curve function; when a total number of at least one third control point is one, a position coordinate of the third initial point is (X3,Y3), a position coordinate of the third control point is (X4,Y4); and a position coordinate of the third terminating point is (X5,Y5);
wherein n represents the total number of the at least one third control point plus 1; Wi represents a weight of the ith point; and t represents a ratio of a length between a predetermined point and the third initial point to a total length of the third profile curve;
wherein constraints of the second profile curve are X3=X5; Y3≧Y4≧Y5; and 0≦Wi≦1.

7. The light guide element of claim 1, wherein the first reflecting surface is formed from a plurality of first reflecting curved surfaces, wherein each of the first reflecting curved surfaces is constructed by the first profile curve.

8. The light guide element of claim 1, wherein the second reflecting surface is formed from a plurality of second reflecting curved surfaces, wherein each of the second reflecting curved surfaces is constructed by the second profile curve.

9. A lamp, comprising:
a light guide element being an annular frustum, comprising:
a light-incident surface having a first outer peripheral edge and a first inner peripheral edge;
a light-emitting surface which is opposite to the light-incident surface and has a second outer peripheral edge and a second inner peripheral edge;
a first reflecting surface connecting the first outer peripheral edge and the second outer peripheral edge, wherein the first reflecting surface is a curved surface constructed by a first profile curve, wherein the first profile curve is a connecting line from a first initial point on the first outer peripheral edge to a first terminating point on the second outer peripheral edge; and
a second reflecting surface connecting the first inner peripheral edge and the second inner peripheral edge, wherein the second reflecting surface is a curved surface constructed by a second profile curve, wherein the second profile curve is a connecting line from a second initial point on the first inner peripheral edge to a second terminating point on the second inner peripheral edge; and
a light source, wherein a light generated from the light source enters the light guide element from the light-incident surface and emits out of the light-emitting surface to generate a predetermined light beam angle of the light.