Patent Publication Number: US-9903559-B2

Title: Lighting apparatus and lens structure thereof

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwanese Application Serial Number 104112731, filed Apr. 21, 2015, which is herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a lighting apparatus. More particularly, the present invention relates to a lighting apparatus and a lens structure thereof. 
     Description of Related Art 
     A typical LED package has a fixed beam angle such as 120 degrees. In order to satisfy optical characteristics of various lighting module, a second lens is employed to cover the LED package to adjust the illumination distribution of the LED. 
     The LED package includes an LED chip, a reflective cup and a fluorescent material. The fluorescent material and the LED chip are encapsulated in the recess of the reflective cup. Because the LED package emits a light only through its top surface, the shapes of the light incident surface and the light outgoing surface of the second lens are designed only based on the illumination distribution of the top surface of the LED package. 
     In pace with the manufacturing progress, a fluorescent film is employed to direct cover the LED chip, and in such a configuration, the LED chip is not required to be encapsulated in the reflective cup. However, since the reflective cup is omitted, the lateral surface of the LED chip emits light to the circuit board, and this light will be reflected to the second lens, which causes unduly high brightness above the LED chip. 
     SUMMARY 
     The present invention prevents the unduly high brightness issue at the location above the light element caused by the light reflected by the circuit board. 
     In accordance with one embodiment of the present invention, a lighting apparatus includes a circuit board, a lighting element and a lens structure. The lighting element is disposed on the circuit board. The lighting element includes a lighting top surface and a lighting lateral surface. The lighting lateral surface is adjoined to the lighting top surface and the circuit board. The lighting top surface has a center and an optical axis. The optical axis passes through the center. The lens structure covers the lighting element for receiving a light from the lighting element. The lens structure includes an outer surface. The outer surface includes a total reflection portion and a light outgoing portion. The optical axis passes through the total reflection portion. The light outgoing portion surrounds the total reflection portion. The total reflection portion is configured to totally reflect a portion of light from the center. The light outgoing portion is configured to allow another light from the center to leave away from the lens structure. 
     In accordance with another embodiment of the present invention, a lens structure includes a bottom surface, an inner surface and an outer surface. The inner surface is caved in the bottom surface. The outer surface includes a total reflection portion and a light outgoing portion. The light outgoing portion surrounds the total reflection portion. A central axis of the lens structure and an imaginary coplanar plane coplanar with the bottom surface crosses at a crossover point. The total reflection portion substantially satisfies: 
     
       
         
           
             
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     Q 1  is a first point on the total reflection portion. Q 2  is a second point immediately adjacent to the first point. Q 3  is a third point located on a connection line connecting the second point and the crossover point. A connection line connecting the third point and the first point is substantially perpendicular to a connection line connecting the crossover point and the first point. R 1  is a distance from the crossover point to the first point. ΔR 1  is a distance from the second point to the third point. Δθ 1  is an included angle defined by the connection line connecting the first point and the crossover point and the connection line connecting the second point and the crossover point. n is a refractive index of a material of the lens structure. 
     By the foregoing embodiment, because some lights emitted by the center of the lighting top surface of the lighting element is totally reflected by the total reflection portion, the brightness above the lighting element will not be unduly high even though the light emitted by the lighting lateral surface is reflected by the circuit board upwardly. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       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. 1  is a cross-sectional view of a lighting apparatus in accordance with one embodiment of the present invention; 
         FIG. 2  is a fragmentary side view of the lens structure in  FIG. 1 ; 
         FIG. 3  is a fragmentary side view of the lens structure in  FIG. 2 ; 
         FIG. 4  is a fragmentary side view of the lens structure in  FIG. 2 ; 
         FIG. 5  is a brightness distribution comparison chart in accordance one experimental result of the present invention; and 
         FIG. 6  is a fragmentary side view of the lighting apparatus in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 1  is a cross-sectional view of a lighting apparatus in accordance with one embodiment of the present invention. As shown in  FIG. 1 , in this embodiment, the lighting apparatus includes a circuit board  100 , a lighting element  200  and a lens structure  300 . The lighting element  200  is disposed on the circuit board  100 , and it can be driven by the driving circuit (not shown) on the circuit board  100  to emit a light. The lens structure  300  covers the lighting element  200  for receiving a light from the lighting element  200  and adjusting the traveling path of the light, so as to generate a desired illumination distribution. The lighting element  200  has a lighting top surface  201  and a lighting lateral surface  202 . The lighting lateral surface  202  is adjoined to the lighting top surface  201  and the circuit board  100 . More particularly, the circuit board  100  has an upper surface  101  facing toward the lens structure  300 . The lighting element  200  is disposed on the upper surface  101  of the circuit board  100 , and the lighting lateral surface  202  is adjoined to the lighting top surface  201  and the upper surface  101  of the circuit board  100 . The lighting top surface  201  and the lighting lateral surface  202  of the lighting element  200  both allow the light inside the lighting element  200  to be emitted outside the lighting element  200 . 
     For example, in some embodiments, the lighting element  200  includes an LED chip  210  and a wavelength converting cover  220 . The LED chip  210  is disposed on the upper surface  101  of the circuit board  100 . In other words, the lower surface of the LED chip  210  is fixed on the upper surface  101  of the circuit board  100 . The wavelength converting cover  220  covers other surfaces of the LED chip  210  (including top and lateral surfaces of the LED chip  210 ), so as to covert the wavelength of lights emitted by these surfaces of the LED chip  210 , thereby obtaining lights having desired wavelength. Light emitted by these surfaces of the LED chip  210  travels through the wavelength converting cover  220  and travel out of the lateral and top surfaces of the wavelength converting cover  220 . As such, the lateral surface of the wavelength converting cover  220  is the lighting lateral surface  202  of the lighting element  200 , and the top surface of the wavelength converting cover  220  is the lighting top surface  201  of the lighting element  200 . In some embodiment, the LED chip  210  can be, but is not limited to, a blue LED chip or an UV LED chip. The wavelength converting cover  220  can be, but is not limited to, a fluorescent film, which coverts some blue lights or UV lights to red, green or yellow light. 
     Because the lighting lateral surface  202  allows the light from the LED chip  210  to be emitted outwardly, and the lighting lateral surface  202  is adjoined to the top surface  101  of the circuit board  100 , the light from the LED chip  210  may travel through the lighting lateral surface  202  to the upper surface  101  of the circuit board  100 . When the light arrives at the upper surface  101  of the circuit board  101 , it is reflected by the upper surface  101  upwardly, which causes unduly high brightness above the lighting element  200 . 
     In order to address the unduly high brightness issue, the present invention provides the following solution. As shown in  FIG. 1 , the lens structure  300  includes an outer surface  310  and an inner surface  320  opposite to each other. The inner surface  320  is closer to the lighting element  200  than the outer surface  310  is, so that the light emitted by the lighting element  200  travels into the lens structure  300  through the inner surface  320  and leaves away from the lens structure  300  through the outer surface  310 . In this embodiment, the outer surface  310  includes a total reflection portion  311  and a light outgoing portion  312 . The lighting top surface  201  has a center O and an optical axis A. The optical axis A passes through the center O and is perpendicular to the lighting top surface  201 . The optical axis A passes through the total reflection portion  311 , and the light outgoing portion  312  surrounds the total reflection portion  311 . When the lighting element  200  emits lights, the total reflection portion  311  totally reflects a portion of light from the center O of the lighting top surface  201 , and the light outgoing portion  312  allows another light from the center O to leave away from the lens structure  300 . 
     In the foregoing embodiment, because some light emitted by the center O of the lighting top surface  201  is totally reflected by the total reflection portion  311 , the brightness above the lighting element  200  will not be unduly high even though the light emitted by the lighting lateral surface  202  is reflected by the upper surface  101  of the circuit board  100  upwardly. 
       FIG. 2  is a fragmentary side view of the lens structure  300  in  FIG. 1 . As shown in  FIG. 2 , the total reflection portion  311  and the light outgoing portion  312  cross at a boundary  313 . In other words, a portion of the outer surface  310  between the boundary  313  and the optical axis A is the total reflection portion  311 , and other portion of outer surface  310  is the light outgoing portion  312 . The boundary  313  and the center O define an imaginary connection line L 1 . The imaginary connection line L 1  and the optical axis A define an included angle α. The included angle α ranges from 6 degrees to 18 degrees. Because the included angle α determines the location of the boundary  313 , it can determine the covering area that the total reflection portion  311  covers. In the covering area of the total reflection portion  311  based on the foregoing range of the included angle α, the brightness above the lighting element  200  (See  FIG. 1 ) is not unduly high. 
     In order to facilitate the total reflection portion  311  to totally reflect the light from the center O, in some embodiments, one embodiment of the present invention provides the following solution. Reference can be now made to  FIG. 3 , which is a fragmentary side view of the lens structure  300  in  FIG. 2 . As shown in  FIG. 3 , the total reflection portion  311  has a first point Q 1  and a second point Q 2 . The first point Q 1  and the second point Q 2  are immediately adjacent to each other. It is understood that in this context, the description “two points are immediately adjacent to each other” means that the two points are arranged at an extremely short interval, such that the tangent plane of one point passes another point. For example, the second point Q 2  and the first point Q 1  are arranged at an extremely short interval, such that the tangent plane of the first point Q 1  passes through the second point Q 2 . A third point Q 3  can be determined on the connection line from the second point Q 2  to the center O. The connection line connecting the third point Q 3  and the first point Q 1  is substantially perpendicular to a connection line connecting the center O and the first point Q 1 . R 1  is a distance from the center O to the first point Q 1 . ΔR 1  is a distance from the second point Q 2  to the third point Q 3 . Δθ 1  is an included angle defined by the connection line connecting the first point Q 1  and the center O and the connection line connecting the second point Q 2  and the center O. n is a refractive index of a material of the lens structure  300 . The total reflection portion  311  substantially satisfies: 
     
       
         
           
             
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     When the total reflection portion  311  substantially satisfies the foregoing equation, the total reflection portion  311  can effectively totally reflect the light from the center O. The working principle is described as follows. The medium outside the outer surface  310  is air, in which the refractive index therefore is 1. The medium inside the outer surface  310  is the material of the lens structure  300 , in which the refractive index is n. According to Snell&#39;s Law, when the light travels from the interior with respect to the outer surface  310  to the outer surface  310 , refraction occurs. If the incident angle is θ i , and the refraction angle is θt, they satisfy: n×sin θ i =1×sin θ t . When a total reflection occurs, the refraction angle θt is 90 degrees, and n×sin θ i =1×sin 90°=1. Therefore, the incident angle satisfies: 
               θ   i     =       arcsin   ⁡     (     1   n     )       .           
In such a situation, the incident angle θ i  is called the critical angle. Therefore, the incident angle θ i  preferably satisfies
 
                 θ   i     &gt;     arcsin   ⁡     (     1   n     )         ,         
so as to ensure that the total reflection occurs when the light travels from the interior with respect to the outer surface  310  to the outer surface  310 . Further, because the connection line connecting the third point Q 3  and the first point Q 1  is substantially perpendicular to the traveling direction of the incident light, the incident angle θ i  is equal to the angle ∠Q 2 Q 1 Q 3 . Therefore, when satisfying
 
                 ∠   ⁢           ⁢   Q   ⁢           ⁢   2   ⁢   Q   ⁢           ⁢   1   ⁢   Q   ⁢           ⁢   3     &gt;     arcsin   ⁡     (     1   n     )         ,         
the total reflection occurs when the light emitted from the center O arrives at the outer surface  311 . Moreover, because the first point Q 1  and the second point Q 2  are arranged at an extremely short interval, the Δθ 1  is extremely small, and therefore, the distance from the first point Q 1  to the third point Q 3  is about R 1 ·Δθ 1 . As a result, the angle ∠Q 2 Q 1 Q 3  satisfies:
 
               ∠   ⁢           ⁢   Q   ⁢           ⁢   2   ⁢   Q   ⁢           ⁢   1   ⁢   Q   ⁢           ⁢   3     =       arctan   ⁡     (       Δ   ⁢           ⁢   R   ⁢           ⁢   1       R   ⁢           ⁢   1   ⁢           ⁢   •   ⁢           ⁢   Δθ1       )       .           
Based on the foregoing principle, as long as the total reflection portion  311  satisfies:
 
                 ∠   ⁢           ⁢   Q   ⁢           ⁢   2   ⁢   Q   ⁢           ⁢   1   ⁢   Q   ⁢           ⁢   3     =       arctan   ⁡     (       Δ   ⁢           ⁢   R   ⁢           ⁢   1       R   ⁢           ⁢   1   ⁢           ⁢   •   ⁢           ⁢   Δθ1       )       &gt;     arcsin   ⁡     (     1   n     )           ,         
the total reflection occurs when the light emitted by the center O arrives at the outer surface  310 , thereby addressing the unduly high brightness issue above the lighting element  200 .
 
     In order to facilitate the light outgoing portion  312  to allow the light emitted by the center O to leave away from the outer surface  310 , one embodiment of the present invention provides the following solution. Reference can be now made to  FIG. 4 , which is a fragmentary side view of the lens structure  300  in  FIG. 2 . As shown in  FIG. 4 , the light outgoing portion  312  has a fourth point Q 4  and a fifth point Q 5 . The fourth point Q 4  and the fifth point Q 5  are immediately adjacent to each other. More particularly, the fifth point Q 5  and the fourth point Q 4  are arranged at an extremely short interval, such that the tangent plane of the first point Q 4  passes through the second point Q 5 . A sixth point Q 6  can be determined on the connection line from the fifth point Q 5  to the center O. The connection line connecting the sixth point Q 6  and the fourth point Q 4  is substantially perpendicular to a connection line connecting the center O and the fourth point Q 4 . R 2  is a distance from the center O to the fourth point Q 4 . ΔR 2  is a distance from the fifth point Q 5  to the sixth point Q 6 . Δθ 2  is an included angle defined by the connection line connecting the fourth point Q 4  and the center O and the connection line connecting the fifth point Q 5  and the center O. The light outgoing portion  312  substantially satisfies: 
     
       
         
           
             
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     When the light outgoing portion  312  substantially satisfies the foregoing equation, the light outgoing portion  312  allows the light from the center O to leave away from the outer surface  310 . The working principle is described as follows. The medium outside the outer surface  310  is air, in which the refractive index therefore is 1. The medium inside the outer surface  310  is the material of the lens structure  300 , in which the refractive index is n. According to Snell&#39;s Law, when incident angle θ i  of which the light arrives at the outer surface  310  satisfies: 
                 θ   i     =     arcsin   ⁡     (     1   n     )         ,         
the total reflection occurs so that the light cannot leave away from the outer surface  310 . Therefore, the incident angle θ i  preferably satisfies
 
                 θ   i     &lt;     arcsin   ⁡     (     1   n     )         ,         
so as to ensure that the light can leave away from the outer surface  310  in a refraction manner when the light travels from the interior with respect to the outer surface  310  to the outer surface  310 . Further, because the connection line connecting the sixth point Q 6  and the fourth point Q 4  is substantially perpendicular to the traveling direction of the incident light, the incident angle θ i  is equal to the angle ∠Q 5 Q 4 Q 6 . Therefore, when satisfying
 
                 ∠   ⁢           ⁢   Q   ⁢           ⁢   5   ⁢   Q   ⁢           ⁢   4   ⁢   Q   ⁢           ⁢   6     &lt;     arcsin   ⁡     (     1   n     )         ,         
the light emitted by the center O can be refracted from the interior with respect to the outer surface  310  to the exterior with respect to the outer surface  310 . Moreover, because the fourth point Q 4  and the fifth point Q 5  are arranged at an extremely short interval, the Δθ 2  is extremely small, and therefore, the distance from the fourth point Q 4  to the sixth point Q 6  is about R 2 ·Δθ 2 . As a result, the angle ∠Q 5 Q 4 Q 6  satisfies:
 
               ∠   ⁢           ⁢   Q   ⁢           ⁢   5   ⁢   Q   ⁢           ⁢   4   ⁢   Q   ⁢           ⁢   6     =       arctan   ⁡     (       Δ   ⁢           ⁢   R   ⁢           ⁢   2       R   ⁢           ⁢   2   ⁢           ⁢   •   ⁢           ⁢   Δθ2       )       .           
Based on the foregoing principle, as long as the light outgoing portion  312  satisfies:
 
                 ∠   ⁢           ⁢   Q   ⁢           ⁢   5   ⁢   Q   ⁢           ⁢   4   ⁢   Q   ⁢           ⁢   6     =       arctan   ⁡     (       Δ   ⁢           ⁢   R   ⁢           ⁢   2       R   ⁢           ⁢   2   ⁢           ⁢   •   ⁢           ⁢   Δθ2       )       &lt;     arcsin   ⁡     (     1   n     )           ,         
the light emitted by the center O can be refracted out of the outer surface  310  when the light arrives at the outer surface  310 , thereby facilitating lighting.
 
     In some embodiments, as shown in  FIG. 2 , the lens structure  300  has a central axis C. The central axis C overlaps with the optical axis A of the lighting top surface  201  (See  FIG. 1 ). In other words, the lens structure  300  is axisymmetrical with respect to the optical axis A of the lighting top surface  201 . The lens structure  300  includes a bottom surface  330  and a lateral surface  340 . The inner surface  320  is caved in the bottom surface  330 . The lateral surface  340  is adjoined to the outer surface  310  and the bottom surface  330 . The bottom surface  330  has an imaginary coplanar plane P. The imaginary coplanar plane P means an imaginary plane extending from the bottom surface  330 , which is coplanar with the bottom surface  330 . The central axis C and the imaginary coplanar plane P coplanar with the bottom surface  330  cross at a crossover point I. The crossover point I overlaps with the center O of the lighting top surface  201 . In other words, in  FIG. 3 , the third point Q 3  is also located on the connection line connecting the second point Q 2  and the crossover point I. The connection line connecting the third point Q 3  and the first point Q 1  is also substantially perpendicular to the connection line connecting the crossover point I and the first point Q 1 . R 1  is also a distance from the crossover point I to the first point Q 1 . Δθ 1  is also an included angle defined by the connection line connecting the first point Q 1  and the crossover point I and the connection line connecting the second point Q 2  and the crossover point I. Moreover, in  FIG. 4 , the sixth point Q 6  is also located on the connection line connecting the firth point Q 5  and the crossover point I. The connection line connecting the sixth point Q 6  and the fourth point Q 4  is substantially perpendicular to the connection line connecting the crossover point I and the fourth point Q 4 . R 2  is also a distance from the crossover point I to the fourth point Q 4 . Δθ 2  is an included angle defined by the connection line connecting the fourth point Q 4  and the crossover point I and the connection line connecting the fifth point Q 5  and the crossover point I. 
     In some embodiments, as shown in  FIG. 2 , the outer surface  310  substantially satisfies:
 
 Y=− 0.0004 X   6 +0.0090 X   5 −0.0790 X   4 +0.3410 X   3 −0.8387 X   2 +1.3205 X+ 3.52.
 
     Y is a distance from any point on the outer surface  310  to the center O (or the crossover point I) measured along a direction parallel to the optical axis A (or the central axis C), namely, the longitudinal distance in  FIG. 2 , X is a distance from the point on the outer surface  310  to the optical axis A measured along a direction perpendicular to the optical axis A, namely, the transversal distance in  FIG. 2 . When the outer surface  310  substantially satisfies the foregoing equation, the total reflection portion  311  can reflect the light emitted by the center O in a total reflection manner, and the light outgoing portion  312  can allow the light emitted by the center O to leave away from the outer surface  310 . 
     In some embodiments, as shown in  FIG. 2 , the inner surface substantially satisfies:
 
 y=− 1.395 x   5 +5.113 x   4 −6.742 x   3 +3.060 x   2 −0.698 x+ 3.
 
     y is a distance from any point on the inner surface  320  to the center O (or the crossover point I) measured along a direction parallel to the optical axis A (or the central axis C), namely, the longitudinal distance in  FIG. 2 , x is a distance from the point on the inner surface  320  to the optical axis A (or the central axis C) measured along a direction perpendicular to the optical axis A (or the central axis C), namely, the transversal distance in  FIG. 2 . When the inner surface  320  substantially satisfies the foregoing equation, and the outer surface  310  substantially satisfies:
 
 Y=− 0.0004 X   6 +0.0090 X   5 −0.0790 X   4 +0.3410 X   3 −0.8387 X   2 +1.3205 X+ 3.52,
 
it is preferably to ensure the total reflection portion  311  to totally reflect the light emitted by the center O, and to ensure the light outgoing portion allows the light emitted by the center O to leave away from the outer surface  310 .
 
     In some embodiments, as shown in  FIG. 2 , the inner surface  320  is a curved surface, the transversal distance from any point on this curved surface to the center O (or the crossover point I) is inversely proportional to the longitudinal distance from this point to the center O (or the crossover point I). The light outgoing portion  312  includes a curved zone  3121  and a planar zone  3122 . The curved zone  3121  is adjoined between the total reflection portion  311  and the planar zone  3122 . The planar zone  3122  is adjoined to the lateral surface  340 . The curved zone  3121  and the planar zone  3122  cross at a boundary  3123 . The planar zone  3122  and the lateral surface  340  cross at a boundary  350 . The inner surface  320  and the bottom surface  330  cross at a boundary  360 . A distance d 1  is defined from the boundary  360  to the optical axis A (or the central axis C) along the direction perpendicular to the optical axis A (or the central axis C). A distance d 2  is defined from the boundary  3123  to the optical axis A (or the central axis C) along the direction perpendicular to the optical axis A (or the central axis C). A distance d 3  is defined from the boundary  350  to the optical axis A (or the central axis C) along the direction perpendicular to the optical axis A (or the central axis C). The relationship among the distances d 1 , d 2  and d 3  preferably satisfies: 4≦d 2 /d 1 ≦6, and d 3 &gt;d 2 . This relationship effectively enables the light to be totally reflected by the total reflection portion  311 , and effectively enables the light to leave away from the lens structure  300  through the light outgoing portion  312 . 
     In some embodiments, as shown in  FIG. 2 , the maximal distance from the inner surface  320  to the center O (or the crossover point I) measured along the direction parallel to the optical axis A (or the central axis C) is the distance d 4 . A distance d 5  is defined from the planar zone  3122  to the center O (or the crossover point I) along the direction parallel to the optical axis A (or the central axis C). The maximal distance from the outer surface  310  to the center O (or the crossover point I) along the direction parallel to the optical axis A (or the central axis C) is the distance d 6 . The relationship among the distances d 4 , d 5  and d 6  preferably satisfies: 1.2≦d 6 /d 4 ≦1.8, and d 5 &gt;0.5 mm. This relationship effectively enables the light to be totally reflected by the total reflection portion  311 , and effectively enables the light to leave away from the lens structure  300  through the light outgoing portion  312 . 
     In some embodiments, a material of the lens structure  300  is a light permeable plastic material which has a refractive index ranging from 1.45 to 1.65. It is understood that “a value ranging from A to B” in this context not only means that this value can be any value higher than A and lower than B, but also means that this value can be equal to A or equal to B. 
       FIG. 5  is a brightness distribution comparison chart in accordance one experimental result of the present invention. As shown in  FIG. 5 , the traditional curve V 1  is a brightness distribution curve of a traditional lighting apparatus employing a traditional lens structure without total reflection portion, and the improved curve V 2  is a brightness distribution curve of the lighting apparatus employing the lens structure  300  in accordance with the present invention. It can be acknowledged that the central portion of the traditional curve V 1  significantly raises, which means that the brightness above the lighting element  200  is unduly high; contrarily, the improved curve V 2  does not significantly raise, which means that the brightness above the lighting element  200  is not unduly high. Therefore, the lens structure  300  can effectively address the issue of the unduly high brightness above the lighting element  200 . 
       FIG. 6  is a fragmentary side view of the lighting apparatus in accordance with another embodiment of the present invention. As shown in  FIG. 6  the main difference between this embodiment and the previous embodiments is that the outer surface  310   a  is partially rough, while the foregoing outer surface  310  is smooth. In particular, the total reflection portion  311   a  of the outer surface  310   a  is rough. For example, the total reflection portion  311   a  has a roughness of between VDI 10 to 30. The “VDI” in this context is the surface roughness value regulated by Verein Deutscher Ingenieure, the Society of German Engineers. By making the total reflection portion  311   a  rough, the brightness distribution curve can be smoother. 
     In some embodiments, as shown in  FIG. 6 , not only the whole total reflection portion  311   a  is rough, but also the light outgoing portion  312  is partially rough. In particular, the light outgoing portion  312   a  has a rough zone  3124   a  and a smooth zone  3125   a . The rough zone  3124   a  is adjoined between the smooth zone  3125   a  and the total reflection portion  311   a . In other words, a zone of the light outgoing portion  312   a  that is closer to the total reflection portion  311   a  is rough, and a zone of the light outgoing portion  312   a  that is farther away from the total reflection portion  311   a  is smooth. The rough zone  3124   a  is rougher than the smooth zone  3125   a . For example, the rough zone  3124   a  has a roughness of between VDI 10 to 30. The rough zone  3124   a  and the smooth zone  3125   a  cross at a boundary  3126   a . The center O (or the crossover point I) and the boundary  3126   a  define an imaginary connection line L 2 . The imaginary connection line L 2  and the optical axis A (or the central axis C) define an included angle β, the included angle β is less than 36 degrees. The included angle β defines the location of the crossover boundary  3126   a , thereby defining the covering area covered by the rough total reflection portion  311   a  and the rough zone  3124   a . In the covering area of the total reflection portion  311   a  and the rough zone  3124   a , the illumination distribution can be smoother. 
     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.