Light guide element for controlling light shape

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,

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there is at least one first control point between the first initial point and the first terminating point; P i represents a position coordinate of an i th 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 (X 0 ,Y 0 ); a position coordinate of the first control point is (X 1 ,Y 1 ); and a position coordinate of the first terminating point is (X 2 ,Y 2 );

wherein n represents the total number of the at least one first control point plus 1; W i represents a weight of the i th 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

≦

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2

;

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°

≧

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≧

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;

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+

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;

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;

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2

≧

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°

-

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1

;

and

0

≦

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i

≦

1

;

wherein α 1 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; α 2 represents an angle included between a horizontal line and a connecting line from the first initial point to the first terminating point, θ 1 represents a refracting angle of the at least one light beam entering from outside of the light guide element; θ 2 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 n material 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,

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;

there is at least one second control point between the second initial point and the second terminating point; P i represents a position coordinate of an i th 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, W i represents a weight of the i th 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

′

;

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≦

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1

′

=

θ

1

′

+

θ

2

′

-

90

⁢

°

;

θ

1

′

=

sin

-

1

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(

1

n

material

)

;

θ

2

′

≧

90

⁢

°

-

θ

1

′

;

and

0

≦

W

i

≦

1

;

wherein α 1 ′ 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; α 2 ′ represents an angle included between a horizontal line and a connecting line from the second initial point to the second terminating point, θ 1 ′ represents a refracting angle of the at least one light beam entering from outside of the light guide element; θ 2 ′ 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 n material 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,

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t

)

=

∑

i

=

0

n

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1

-

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)

n

-

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i

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W

i

∑

i

=

0

n

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(

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 P i represents a position coordinate of an i th 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 (X 3 ,Y 3 ), a position coordinate of the third control point is (X 4 ,Y 4 ); and a position coordinate of the third terminating point is (X 5 ,Y 5 );

wherein n represents the total number of the at least one third control point plus 1; W i represents a weight of the i th 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 X 3 =X 5 ; Y 3 ≧Y 4 ≧Y 5 ; and 0≦W i ≦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.