WO2013131860A1 - Lens and illuminating device having the lens - Google Patents

The present invention relates to a lens for an illuminating device (100), having a base (1) and a region protruding from the base (1) to define an accommodating cavity for accommodating a light source (5) of the illuminating device (100), wherein the protruding region has one surface facing away from the light source (5) configured as an emergent surface (2) and one surface facing to the light source (5) configured as an incident surface (4), and wherein the emergent surface (2) and the incident surface (4) are symmetrical with respect to a first symmetric plane (V1) passing through an optical axis (A) of the light source (5), and asymmetrical with respect to a second symmetric plane (V2) passing through the optical axis (A) and perpendicular to the first symmetric plane (V1), and wherein curves of the emergent surface (2) and the incident surface (4) are configured in such a manner that light emitted from the light source (5) produces a uniform luminance (L) after emitted from the emergent surface (2) at various angles and reflected by various positions of an illuminated surface (S) of an object to be illuminated. The present invention also relates to an illuminating device (100) having such lens.

Description

Lens and Illuminating Device Having the Lens Technical Field

The present invention relates to a lens for an illuminating device. In addition, the present invention also relates to an illuminating device having such lens.

Background Art LED light-emitting assembly is widely used in street illumi^¬ nation. However, the light distribution performance of the LED light-emitting assembly cannot meet the requirements of street illumination, thus a secondary lens must be additionally arranged on the top of the LED light-emitting assembly. Almost all the existing lenses are configured based on the illuminance uniformity theory. With such lens, the streetlamp can obtain quite uniform illuminance. But eyes of an observer receive luminance from the road surface, and the luminance itself depends upon the illuminance and a reflection coeffi- cient of the road surface. When the observer is at different positions with respect to the streetlamp, the reflection co^¬ efficient of the road surface will be varied, but the illumi^¬ nance obtained by the prior lens is uniform, that is to say, the illuminance of light emitted from the streetlamp is the same at different positions, then the luminance received by the observer at different positions will be different, which leads to one problem, namely, the illuminance of light emit^¬ ted from the illuminating device using the prior lens is uniform, while the luminance of light reflected by the road sur- face is not sufficient. Summary of the Invention

In order to solve the above technical problem, the present invention provides a lens for an illuminating device, especially for a streetlamp. The lens is configured based on the luminance uniformity theory, and light emitted from the lens of the present invention has uniform luminance after re^¬ flected by the road surface. In addition, the present inven^¬ tion also relates to an illuminating device having such lens.

The first object of the present invention is accomplished via a lens for an illuminating device. The lens has a base and a region protruding from the base to define an accommodating cavity for accommodating a light source of the illuminating device, the protruding region has one surface facing away from the light source configured as an emergent surface and one surface facing to the light source configured as an inci^¬ dent surface, wherein the emergent surface and the incident surface are symmetrical with respect to a first symmetric plane passing through an optical axis of the light source, and asymmetrical with respect to a second symmetric plane passing through the optical axis and perpendicular to the first symmetric plane, wherein curves of the emergent surface and the incident surface are configured in such a manner that light emitted from the light source produces a uniform lumi^¬ nance after emitted from the emergent surface at various an- gles and reflected by various positions of an illuminated surface of an object to be illuminated. The lens of the pre^¬ sent invention is configured based on the luminance uniform^¬ ity theory, that is to say, the luminance of light reflected by various positions of the illuminated surface is firstly set to be uniform, so that profiles of the curves of the in^¬ cident surface and the emergent surface are derived in^¬ versely. According to a preferred solution of the present invention, the curves of the emergent surface and the incident surface are configured in such a manner that light emitted from the emergent surface has an illuminance gradually decreasing in a direction away from a vertical photometric axis, and the il^¬ luminance matches reflection coefficients of different posi^¬ tions of the illuminated surface so as to obtain a uniform luminance. According to the relation between the illuminance and the luminance, it can be known that the luminance depends upon not only the illuminance but also the reflection coeffi^¬ cients of different positions of the illuminated surface. When the luminance is fixed, it can be derived that the illu^¬ minance of light emitted from the emergent surface gradually decreases in a direction away from the vertical photometric axis .

Further according to the present invention, the curves of the emergent surface and the incident surface are configured in such a manner that light emitted from the emergent surface has predetermined vertical photometric angle γ and light in- tensity I so as to obtain the illuminance gradually decreas^¬ ing in a direction away from the vertical photometric axis, wherein the vertical photometric angle is an angle between the light emitted from the emergent surface and the vertical photometric axis. Preferably, the illuminance is calculated

_^ / x (cos v)³

according to the following formula: E = — , where H is a vertical height from the light source to the illuminated sur^¬ face. In solutions of the present invention, the illuminance substantially depends upon the vertical photometric angle and the light intensity of the light emitted from the emergent surface. When the lens of the present invention is config^¬ ured, since the luminance reflected to the observer from various positions of the illuminated surface is uniform, the „

vertical photometric angle and the light intensity of each beam of light emitted from the lens can be obtained, and thus, coordinates of points where each beam light intersects the incident surface and the emergent surface in a 3D space can be obtained by means of a dedicated photo model, and therefore, profiles of the curves of the incident surface and the emergent surface are determined.

According to one preferred solution of the present invention, the reflection coefficient is calculated according to the vertical photometric angle and a deviation angle, wherein the deviation angle is an angle between a first connecting line and an oppositely elongated line of a second connecting line, wherein the first connecting line is between a first intersection point of the vertical photometric axis and the illu^¬ minated surface and a second intersection point of the light emitted from the emergent surface and the illuminated sur^¬ face, and the second connecting line is between a position where an observer is located on the illuminated surface and the second intersection point. In the solutions of the pre^¬ sent invention, the vertical photometric angle is 0-90°, and the deviation angle is 0-180°.

Preferably, the emergent surface comprises a first curve cut off by an upper surface of the base, a second curve cut off by the first symmetric plane and a third curve cut off by the second symmetric plane, and the incident surface comprises a fourth curve cut off by a lower surface of the base, a fifth curve cut off by the first symmetric plane and a sixth curve cut off by the second symmetric plane. Various curves of the emergent surface and the incident surface cooperate with each other so as to produce emitted light having the predetermined vertical photometric angle and light intensity. Advantageously, the first curve is obtained by the following formulae in an xy coordinate system that takes the light source as an origin on the upper surface of the base:

Rj9) = Rc + dr{0) , Rc>(^)xDl and dr(0) < 0.2xRc , where Θ is 0-360°, R(6) is a distance from each point on the first curve to the light source, Rc is a constant, Dl is diameter of the light source, and dr (Θ) is a variable changing with the angle Θ. In the solutions of the present invention, the light source is an LED light source, wherein a diameter of a single LED light source usually is l-5mm.

Advantageously, the second curve is obtained by the following formulae in an xy coordinate system that takes the light source as an origin on the first symmetric plane: f"(x)<0,-Rc<x<Rc , /'(0) = 0 and Rc>(-)xDl .

Further advantageously, the third curve is obtained by the following formulae in an xy coordinate system that takes the light source as an origin on the second symmetric plane: f"(x)<0,-Rc<x<Rc , /'(0) = 0 and Rc>(-)xDl .

Advantageously, the fourth curve is obtained by the following formulae in an xy coordinate system that takes the light source as an origin on the lower surface of the base:

2 2

X V l

— +— = 1 and Ro(—)xDl, where a is a semimajor axis of the a b 2

ellipse, b is a semiminor axis of the ellipse, a value of a is 0. l*Rc-0.9*Rc, a value of b is 0.35*Rc-0.55*Rc, Rc is a constant, and Dl is diameter of the light source.

Advantageously, the fifth curve is obtained by the following formulae in an xy coordinate system that takes the light source as an origin on the first symmetric plane: f "(x) < 0, -a < x < a ; f \x₀) = 0,x₀ < 0 , f(a) = f(-a) = 0 .

Further advantageously, the sixth curve is obtained by the following formulae in an xy coordinate system that takes the light source as an origin on the second symmetric plane: f "(x) < 0, -b < x < b , / '(0) = 0 , f(b) = f(-b) = 0 .

The other object of the present invention is accomplished via an illuminating device comprising the lens above. Light emit- ted from the illuminating device has a uniform luminance af^¬ ter reflected by various positions of the illuminated sur^¬ face .

Brief Description of the Drawings

The accompanying drawings constitute a part of the present Description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention and are used to de^¬ scribe the principles of the present invention together with the Description. In the accompanying drawings the same compo- nents are represented by the same reference numbers. As shown in the drawings :

Fig. 1 is a schematic light path chart of an illuminating de^¬ vice according to the present invention in practical applica^¬ tion; Fig. 2 is a light path chart of the illuminating device ac^¬ cording to the present invention in a plane view;

Fig. 3 is a 3D light path chart of the illuminating device according to the present invention;

Fig. 4 is a chart of reflection coefficients of various posi^¬ tions of an illuminated surface;

Fig. 5 is a perspective view of a lens according to the pre- sent invention;

Fig. 6 is a top view of the lens according to the present in^¬ vention ;

Fig. 7 is a bottom view of the lens according to the present invention ; Fig. 8a is a schematic diagram of a first curve of the lens according to the present invention;

Fig. 8b is a schematic diagram of a second curve of the lens according to the present invention;

Fig. 8c is a schematic diagram of a third curve of the lens according to the present invention;

Fig. 8d is a schematic diagram of a fourth curve of the lens according to the present invention;

Fig. 8e is a schematic diagram of a fifth curve of the lens according to the present invention; and Fig. 8f is a schematic diagram of a sixth curve of the lens according to the present invention.

Detailed Description of the Embodiments

Fig. 1 is a schematic light path chart of an illuminating de- ₀

o

vice 100 according to the present invention in practical ap^¬ plication. It can be seen from Fig. 1 that a road surface as an illuminated surface S receives illuminance E of light emitted from an emergent surface 2 of a lens of the illumi- nating device 100 according to the present invention, and hu^¬ man eyes receive luminance L reflected by the illuminated road surface when viewing the illuminated street. The lens according to the present invention is configured according to the luminance uniformity theory, that is to say, the lumi- nance L reflected to eyes of an observer from various posi^¬ tions of the street is uniform. The luminance L depends upon the illuminance E and the reflection coefficients r of vari^¬ ous positions of the street, namely, L=Exr. When the reflec^¬ tion coefficients r of various positions of the street are determined, illuminance E of each beam of light emitted from the emergent surface 2 can be derived, and accordingly, pro^¬ files of curves of the emergent surface 2 and the incident surface 4 can be calculated.

Fig. 2 is a light path chart of the illuminating device 100 according to the present invention in a plane view. Relationship between the luminance L and the illuminance E can be seen more clearly from Fig. 2. In Fig. 2, beams of light emitted from the emergent surface 2 of the lens are projected on positions PI, P2 and P3 in a certain region S' of the il- luminated surface S. If the lens is configured according to the prior illuminance uniformity theory, the illuminance E of the light emitted from the emergent surface 2 can satisfy the following formula: EP1=EP2=EP3, where EP1, EP2 and EP3 are illuminance of light emitted to PI, P2 and P3. Thus, based on the description of Fig. 1, various positions viewed by the observer have different reflection coefficients, and then, the luminance L reflected to the observer will be varied, that is to say, LP1>LP2>LP3, where LP1, LP2 and LP3 are lumi- _

y

nance of light reflected from PI, P2 and P3, which therefore leads to nonuniform luminance of various positions observed by the observer.

The lens of the present invention is configured according to the luminance uniformity theory, as a result, light paths of light emitted by the illuminated surface S are uniform, i.e. LP1=LP2=LP3. However, since the reflection coefficients of various positions observed by the observer are different, the illuminance E of light emitted from the emergent surface 2 needs to be adjusted, thus it can be estimated that the illu^¬ minance E gradually decreases in a direction facing away from a vertical photometric axis UQT, and consequently, the pro^¬ files of curves of the emergent surface 2 and the incident surface 4 can be calculated according to different values of the illuminance E of respective beams of light.

Fig. 3 is a 3D light path chart of the illuminating device 100 according to the present invention. As can be seen from the light path chart, eyes of the observer see a certain re^¬ gion S' of the illuminated surface S of the road surface, wherein the three observed positions PI, P2 and P3 shown in Fig. 2 are located in the region S' . In Fig. 3, only one po^¬ sition PI thereof is taken as an example for illustration.

According to one solution of the present invention, uniform luminance L is obtained by matching the illuminance E with the reflection coefficients r of different positions of the illuminated surface S. In the precondition of maintaining a constant luminance of beams of light reflected by various po^¬ sitions of the illuminated surface S, the illuminance E of each beam of light emitted from the lens can be obtained, and a vertical photometric angle γ and a light intensity I that determine the illuminance E can be calculated, wherein the vertical photometric angle γ is an angle between light emit^¬ ted from the emergent surface 2 and the perpendicular photo^¬ metric axis UQT, and wherein the illuminance E is calculated

/ x (cos vf

vertical height from the light source 5 to the illuminated surface S .

In addition, the reflection coefficient r related to the lu^¬ minance L is calculated according to the vertical photometric angle γ and a deviation angle β, wherein the deviation angle β is an angle between a first connecting line TP and an oppo^¬ sitely elongated line of a second connecting line OP, wherein the first connecting line TP is between a first intersection point T of the vertical photometric angle γ and the illumi^¬ nated surface S and a second intersection point P of the light emitted from the emergent surface 2 and the illuminated surface S, and the second connecting line OP is between a po^¬ sition 0 where the observer is located on the illuminated surface S and the second intersection point P. The value of the reflection coefficient can be derived according to the chart of reflection coefficients of various positions of the illuminated surface as shown in Fig. 4.

Fig. 5 is a perspective view of a lens according to the pre^¬ sent invention. The lens shown in Fig. 1 is cut off by a first symmetric plane VI . In order to clearly see the inner structure of the lens, Fig. 1 merely shows a lens structure at one side of the first symmetric plane VI. It can be seen from Fig. 1 that the lens of the present invention has a base 1 and a region protruding from the base 1 to define an accommodating cavity 3 for accommodating a light source 5 of the illuminating device 100. The protruding region has one side away from the light source 5 formed as an emergent surface 2 and one side close to the light source 5 formed as an incident surface 4.

Fig. 6 is a top view of the lens according to the present invention, and Fig. 3 is a bottom view of the lens according to the present invention. It can be seen from Fig. 6 and Fig. 7 that that the emergent surface 2 and the incident surface 4 are symmetrical with respect to the first symmetric plane VI passing through an optical axis A of the light source 5, and asymmetrical with respect to a second symmetric plane V2 passing through the optical axis A and perpendicular to the first symmetric plane VI.

In addition, it can be further seen from Fig. 6 and Fig. 7 that the emergent surface 2 comprises a first curve 2a cut off by an upper surface of the base 1, a second curve 2b cut off by the first symmetric plane VI and a third curve 2c cut off by the second symmetric plane V2, and the incident surface 4 comprises a fourth curve 4a cut off by a lower surface of the base 1, a fifth curve 4b cut off by the first symmetric plane VI and a sixth curve 4c cut off by the second sym- metric plane V2.

Fig. 8a is a schematic diagram of the first curve 2a of the lens according to the present invention. It can be seen from Fig. 8a that the curve is similar to a circle. The first curve 2a is obtained by the following formulae in an xy coor- dinate system , that takes the light source 5 as an origin on the upper surface of the base 1: R(6) = Rc + dr{6) , Rc>(^)xDl and dr{6) <0.2xRc , where Θ is 0-360°, R (Θ) is a distance from each point on the first curve 2a to the light source 5, Rc is a constant, Dl is diameter of the light source 5, and dr(d) is a variable changing with the angle Θ. Fig. 8b is a schematic diagram of the second curve 2b of the lens according to the present invention. The second curve 2b is obtained by the following formulae in an xy coordinate system that takes the light source 5 as an origin on the first symmetric plane VI: /"(x) < 0, -Rc < x < Rc , /'(0) = 0 and

Rc > (^) x Dl . According to the present invention, the second curve 2b is asymmetrical with respect to the second symmetri^¬ cal plane V2, and an extending direction of a projection of the second curve 2b on a plane defined by the base 1 is per- pendicular to a longitudinal extending direction of an illuminated surface S. The illuminated surface S is an extending direction of the street in solutions of the present inven^¬ tion.

Fig. 8c is a schematic diagram of the third curve 2c of the lens according to the present invention. The third curve 2c is obtained by the following formulae in an xy coordinate system that takes the light source 5 as an origin on the sec^¬ ond symmetric plane V2 : /"(x) < 0, -Rc < x < Rc , /'(0) = 0 and

Rc > (^) x Dl . According to the present invention, the third curve 2c is symmetrical with respect to the first symmetrical plane VI, and an extending direction of a projection of the third curve 2c on a plane defined by the base 1 is parallel to the illuminated surface S, i.e. parallel to a longitudinal extending direction of the street. Fig. 8d is a schematic diagram of the fourth curve 4a of the lens according to the present invention. The fourth curve 4a is formed as an elliptical curve on the lower surface of the base, wherein the fourth curve 4a is obtained by the follow^¬ ing formulae in an xy coordinate system that takes the light source 5 as an origin on the lower surface of the base 1: — +— = 1 and Ro(—)xDl, where a is a semimajor axis of the a b 2

ellipse, b is a semiminor axis of the ellipse, a value of a is 0. l*Rc-0.9*Rc, a value of b is 0.35*Rc-0.55*Rc. According to the present invention, the semimajor axis a of the fourth curve 4a is perpendicular to the illuminated surface S, i.e. perpendicular to the longitudinal extending direction of the street, and the semiminor axis b is parallel to the longitu^¬ dinal extending direction of the street.

Fig. 8e is a schematic diagram of the fifth curve 4b of the lens according to the present invention. The fifth curve 4b is obtained by the following formulae in an xy coordinate system that takes the light source 5 as an origin on the first symmetric plane VI: f"(x) < 0,-a < x < a ; /'(x₀) = 0,x₀ < 0 , f(a) = f(-a) = 0. According to the present invention, the fifth curve 4b is asymmetrical with respect to the second symmetri^¬ cal plane V2, and an extending direction of a projection of the fifth curve 4b on a plane defined by the base is perpen^¬ dicular to the illuminated surface S, i.e. perpendicular to the longitudinal extending direction of the street. Fig. 8f is a schematic diagram of the sixth curve 4c of the lens according to the present invention. The sixth curve 4c is obtained by the following formulae in an xy coordinate system that takes the light source 5 as an origin on the sec^¬ ond symmetric plane V2 : f"(x) < ,-b < x < b , / '(0) = 0 , f(b) = f(-b) = 0. According to the present invention, the sixth curve 4c is symmetrical with respect to the first symmetrical plane VI, and an extending direction of a projection of the sixth curve 4c on a plane defined by the base 1 is parallel to the illuminated surface S, i.e. parallel to the longitudi- nal extending direction of the street. The above is merely preferred embodiments of the present in^¬ vention but not to limit the present invention. For the per^¬ son skilled in the art, the present invention may have vari^¬ ous alterations and changes. Any alterations, equivalent sub- stitutions, improvements, within the spirit and theory of the present invention, should be covered in the protection scope of the present invention.

,

List of reference signs

100 illuminating device

1 base

2 emergent surface

2a first curve

2b second curve

2c third curve

3 accommodating cavity

4 incident surface

4a fourth curve

4b fifth curve

4c sixth curve

5 light source

VI first symmetrical plane

V2 second symmetrical plane

L luminance

E illuminance

r reflection coefficient , ,

1 b

S illuminated surface

S' a certain region of the illuminated surface

I light intensity

Y vertical photometric angle β deviation angle

UQT vertical photometric axis

H vertical height from the light source 5 to the illuminated surface S

T first intersection point of the vertical photometric angle UQT and the illuminated surface S

TP first connecting line

0 position where the observer is located on the illuminated surface S

OP second connecting line PI, P2, P3 observed positions in a certain region S' of the illuminated surface S

Claims

1. A lens for an illuminating device (100), wherein the lens has a base (1) and a region protruding from the base (1) to define an accommodating cavity (3) for accommodating a light source (5) of the illuminating device (100), the pro^¬ truding region has one surface facing away from the light source (5) formed as an emergent surface (2) and one surface facing to the light source (5) formed as an incident surface (4), characterized in that the emergent surface (2) and the incident surface (4) are symmetrical with respect to a first symmetric plane (VI) passing through an optical axis (A) of the light source (5) , and asymmetrical with respect to a sec^¬ ond symmetric plane (V2) passing through the optical axis (A) and perpendicular to the first symmetric plane (VI), wherein curves of the emergent surface (2) and the incident surface (4) are configured in such a manner that light emitted from the light source (5) produces a uniform luminance (L) after emitted from the emergent surface (2) at various angles and reflected by various positions of an illuminated surface (S) of an object to be illuminated.

2. The lens according to Claim 1, characterized in that the curves of the emergent surface (2) and the incident surface

(4) are configured in such a manner that light emitted from the emergent surface (2) has the illuminance (E) gradually decreasing in a direction away from a vertical photometric axis (UQT) , the illuminance (E) matches reflection coeffi^¬ cients (r) of different positions of the illuminated surface

(5) so as to obtain the uniform luminance (L) .

3. The lens according to Claim 2, characterized in that the curves of the emergent surface (2) and the incident surface (4) are configured in such a manner that light emitted from the emergent surface (2) has predetermined vertical photomet^¬ ric angle (γ) and light intensity (I) so as to obtain the il^¬ luminance (E) gradually decreasing in a direction away from the vertical photometric axis (UQT) , wherein the vertical photometric angle (γ) is an angle between the light emitted from the emergent surface (2) and the vertical photometric axis (UQT) .

4. The lens according to Claim 3, characterized in that the illuminance (E) is calculated according to the following for-

_^ / x (cos v)³

mula: E = , where H is a vertical height from the

H

light source (5) to the illuminated surface (S) .

5. The lens according to Claim 3, characterized in that the reflection coefficient (r) is calculated according to the vertical photometric angle (γ) and a deviation angle (β), wherein the deviation angle (β) is an angle between a first connecting line (TP) and an oppositely elongated line of a second connecting line (OP) , wherein the first connecting line (TP) is between a first intersection point (T) of the vertical photometric axis (UQT) and the illuminated surface (S) and a second intersection point (P) of the light emitted from the emergent surface (2) and the illuminated surface (S) , and the second connecting line (OP) is between a posi^¬ tion (0) where an observer is located on the illuminated sur^¬ face (S) and the second intersection point (P) .

6. The lens according to any one of Claims 2-5, character^¬ ized in that the emergent surface (2) comprises a first curve (2a) cut off by an upper surface of the base (1), a second curve (2b) cut out by the first symmetric plane (VI) and a third curve (2c) cut off by the second symmetric plane (V2), and the incident surface (4) comprises a fourth curve (4a) cut off by a lower surface of the base (1), a fifth curve (4b) cut off by the first symmetric plane (VI) and a sixth curve (4c) cut off by the second symmetric plane (V2) .

7. The lens according to Claim 6, characterized in that the first curve (2a) is obtained by the following formulae in an xy coordinate system that takes the light source (5) as an origin on the upper surface: R(0) = Rc + dr(0) , Ro (-^) x Dl and dr{9) < 0.2 x Rc , where Θ is 0-360°, R(d) is a distance from each point on the first curve (2a) to the light source (5) , Rc is a constant, Dl is diameter of the light source (5), and dr (Θ) is a variable changing with the angle Θ.

8. The lens according to Claim 7, characterized in that the second curve (2b) is obtained by the following formulae in an xy coordinate system that takes the light source (5) as an origin on the first symmetric plane (VI) : /"(x) < 0, -Rc < x < Rc ,

/ '(0) = 0 and Rc > (^) x Dl .

9. The lens according to Claim 8, characterized in that the third curve (2c) is obtained by the following formulae in an xy coordinate system that takes the light source (5) as an origin on the second symmetric plane (V2) : /"(x) < 0, -Rc < x < Rc ,

/ '(0) = 0 and Rc > (^) x Dl .

10. The lens according to Claim 6, characterized in that the fourth curve (4a) is obtained by the following formulae in an xy coordinate system that takes the light source (5) as an

2 2

origin on the lower surface: —+— = 1 and Ro (—) x Dl , where a a b 2

is a semimajor axis of the ellipse, b is a semiminor axis of the ellipse, a value of a is 0. l*Rc-0.9*Rc, a value of b is 0.35*Rc-0.55*Rc, Rc is a constant, and Dl is diameter of the light source (5) .

11. The lens according to Claim 10, characterized in that the fifth curve (4b) is obtained by the following formulae in an xy coordinate system that takes the light source (5) as an origin on the first symmetric plane (VI): f "(x) < 0, -a < x < a ;

Γ(χ₀) = 0,χ₀ < 0 , /(«) = /(-«) = 0 .

12. The lens according to Claim 11, characterized in that the sixth curve (4c) is obtained by the following formulae in an xy coordinate system that takes the light source (5) as an origin on the second symmetric plane (V2): f "(x) < 0, -b < x < b , / '(0) = 0 , f(b) = f(-b) = 0 .

13. An illuminating device (100), comprising a light source, characterized in that the illuminating device (100) further comprises the lens according to any one of Claims 1-12.

14. The illuminating device (100) according to Claim 13, characterized in that the light source is configured as an LED light source.