CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority and benefits of Chinese Patent Application Serial No.200910107553.6, filed with the State Intellectual Property Office of the P. R. China on May 31, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention The present invention generally relates to light emitting diode (LED) illumination field, and in particular, to a lens for LED and a LED street lamp comprising the same.

Description of the Related Art

Recently, due to the global energy shortage, many countries pay more attention to the new energy developing and energy saving technology. As the rapid development of the LED technology with a significant energy saving effect, the LED is applied in increasing fields, so the LED industry is strongly supported by the government. Besides being used for backlight, indication and decoration, the LED is also widely used as a light source in the illumination industry. In the outdoor illumination field, the power of the lamps for the road illumination is larger than 100 watt, thus resulting in large energy consumption, so that the high power LED lamp gradually replaces the conventional lamp in the road illumination field.

As the development of the LED technology, a power of a high power LED module has reached tens of watts or even hundreds of watts. Using such high power LED module as a light source not only saves quite a few of materials but also simplifies the circuit and the structure design, so that it is advantageous to control the cost. However, the luminescence area of the high power LED module is large, so that it is more difficult to achieve an even beam distribution for the high power LED module than a single LED, and there is no LED lens suitable for the high power LED module recently in the market. SUMMARY OF THE INVENTION

In view of the above problems in the prior art, the present invention is directed to provide a LED lens having an even light spot, and a LED street lamp using the LED lens which may generate an even light spot.

Accordingly, an embodiment of the present invention provides a light emitting diode (LED) lens, comprising a base which is formed with a symmetric light incidence curved surface and a light exit curved surface, wherein the light exit curved surface is positioned above the light incidence curved surface and meets the following equation:

Z = Z ₀ - yjr ² - {x ² + y ² ) + ax ² +by ² + cx ² y ² , where an origin of coordinate is in the center of a bottom of the base; x and y are coordinate axes; and zo, r, a, b and c are aspheric coefficients.

According to an embodiment of the present invention, the LED lens has a symmetric light incidence curved surface and a light exit curved surface, which are designed according to the secondary optical principle and which distribute an emitted beam by the LED to generate a rectangular light spot, so that an uniform illumination may be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention will be better understood from the following detailed description of preferred embodiments of this invention when taken conjunction with the accompanying drawings in which:

Figure 1 is a sectional view of the LED lens according to an embodiment of the present invention.

Figure 2 is a bottom view of the LED lens of according to an embodiment of the present invention. Figure 3 is a light distribution pattern on XOZ plane according to an embodiment of the present invention.

Figure 4 is a light distribution pattern on YOZ plane according to an embodiment of the present invention.

Figure 5 is a sectional view of a LED street lamp of according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION

It will be appreciated by those of ordinary skill in the art that the disclosure can be embodied in other specific forms without departing from the spirit or essential character thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive.

Referring to Figure 1 and Figure 2, the light emitting diode (LED) lens 10 according to an embodiment of the present invention comprises a base 2, the base 2 has a symmetric light incidence curved surface 4 and a light exit curved surface 1, each of the light incidence curved surface 4 and the light exit curved surface 1 may have a central axis (not shown), a recess 3 for receiving a LED is formed at the light incidence curved surface 4. The light incidence curved surface meets the following equation:

Z = Z ₀ - ^r ² - (x ² + y ² ) + ax ² + by ² + cx ² y ² , where an origin of coordinate is at the center of a bottom of the base; x and y are coordinate axes; and z ₀ , r, a, b and c are aspheric coefficients. In some embodiments, z ₀ is in a range of about 30.0-30.1, r is in a range of about 74.0-74.1, a is in a range of about 0.01-0.02, b is in a range of about 0.003-0.005, and c is in a range of about -0.00001- -0.00003.

The lens 100 may have an optical axis A-A. The optical axis A-A locates on, for example,

Z axis of a XYZ coordinate system. In some embodiments, the central axes of the incident curved surface 4 and the exit curved surface 1 coincide with the optical axis A-A, as such both locate on the Z axis. In this manner, the lens may be a coaxial system, thus reducing light loss caused by reflections.

In some embodiments of the present invention, the symmetric light incidence curved surface

4 is a spherical curved surface, an ellipsoidal curved surface, a rectangular curved surface or symmetric irregular curved surface. Referring Figure 2, in this embodiment, the symmetric light incidence curved surface 4 is a spherical curved surface. When viewing from the bottom of the lens to the light exit curved surface, semimajor axis L is along the axis X. semi-minor axis S is along the axis Y. Origin O of the XYZ coordinate system may be at the center of the ellipse. In some embodiment of the invention, the semimajor axis L has a value between 15 mm and 16mm. The symmetric light incidence curved surface 4 primarily distributes the light emitted by the

LED light source. Then the light primarily reaches the light exit curved surface 1, and the light exit curved surface 1 process the light according to the secondary optical principle to further adjust the shape of the light and then cause the exit light to form an even light spot. In some embodiments of the invention, the shape of the light spot is rectangle, and the length of the rectangular area may be four times the width of the rectangular area. The equation of the light exit curved surface is simple, so that the manufacturing procedure of the lens is simplified and the cost of the LED lens is reduced.

In some embodiments of the present invention, when the LED lens is used, the x axis is substantially parallel with the road surface, so that the ellipsoidal curved surface may prevent the light from over diffusing in the short side direction of the rectangular light spot when the light reaches the road. The minor axis of the ellipsoidal curved surface coincides with the y axis, which causes the light to diffuse properly, so that the light will not focus in the y axis direction.

In some embodiments of the invention, the refractive index of the LED lens is about 1.49. The LED lens with such refractive index may reduce the light loss caused by the total reflection in the LED lens. In addition, the material with such refractive index can be selected widely, so that is advantageous to reduce the cost. In some embodiments of the invention, the LED lens is made of a transparent optical acrylic material. The acrylic material may enhance the light transmittance and increase the light energy usage efficiency; meanwhile the acrylic material is a conventional material, which is advantageous to reduce the cost.

In some embodiments of the invention, the length of the semimajor axis of the ellipsoidal curved surface is about 15.5mm and the focal length of the ellipsoidal curved surface is about

24mm. More particularly, in the equation: z = Z ₀ - ^r ² - (x ² + y ² ) + ax ² + by ² + cx ² y ² , z ₀ is about 30, r is about 74.07, a is about 0.013, b is about 0.004 and c is about -0.00002. Under the above condition, the light energy emitted by LED module may be used to the utmost extent, and a high level of illumination uniformity is achieved. FIG. 3 illustrates a light distribution pattern on the XOZ plane according to some embodiments of the present invention. The light exit curved surface 1 refracts the light emitted by the LED and adjusted by the ellipsoidal curved surface 4, and further bunches and adjusts the light, so that the lateral light exited from the light exit curved surface can reaches the road to realize the illumination function, and the light spot satisfies the requirement of the width of the road, and the luminance is uniformed to the utmost extent in the illumination region. FIG. 4 illustrates a light distribution pattern on YOZ plane according to some embodiments of the present invention. The light exit curved surface 1 adjusts and shapes the light emitted by the LED and adjusted by the ellipsoidal curved surface 4. Therefore, on one hand, the lateral light may reach the road to effectively illuminate and some light are supplied to the light spot edges of the both sides, on the other hand, the light energy over concentrated at the center may be diffused to the both sides. Because the lights in different regions are processed via different adjustments, the length of the light spot satisfies the requirements of the illumination. The shape of the light spot is rectangular and the rectangular spot may have the length four times the width. In addition, in the illumination region, the luminance is uniformed to the utmost extent. In some embodiments of the invention, the light is effectively used and reasonably distributed by combination of the ellipsoidal curved surface 4 and light exit curved surface 1 according to the principle of geometrical optics. In the XOZ plane, only two lights of 100 lights will be lost due to the total refraction, and the other lights can all reach the road. In the YOZ plane, there is no light loss due to the total refraction, so that the light energy usage efficiency is high and the light loss is reduced to the utmost extent. The shape of the light spot is rectangular, and the luminance is uniformed to the utmost extent in the illumination region. If a high power LED module is used for the illumination, the light spot has a uniform illumination and there is no shadow between adj acent street lamp s .

In some embodiments of the invention, in the equation: z = Z ₀ ~ ψ ² - (x ² + y ² ) + ax ² +by ² + cx ² y ² , z ₀ may be about 30.05, r may be about 74.09, a may be about 0.019, b may be about 0.0049 and c may be about -0.000029.

The embodiments of invention also provide a street lamp comprising a LED lens described above.

Referring to Figure 5, the street lamp comprises a housing 100; an inner unit comprising a base 200 and a LED module having a circuit board 500, a LED 400 and a LED lens 300. The LED module is disposed on the base 200, and the LED 400 is fixed on the circuit board 500. The housing 100 packs the inner unit. To protect the inner unit, the street lamp further comprises a fin configured to dissipate the heat generated during illumination. In some embodiments of the present invention, the shape of the light spot of the street lamp is rectangular, and the even illumination is achieved. In some embodiments of the present invention, the LED 400 is a LED chip module (referred to as simply the module light source) or a pin type light emitting diode light source packed with a LED chip (referred to as simply the pin type light source). In some embodiments of the present invention, the LED 400 is a LED chip module comprising a plurality of LED chips. The LED chips are fixed on the circuit board 500 by a surface mount technology. The circuit board 500 comprises a driving unit for universally controlling the LED chips. In these embodiments, the LED street lamp with the above mentioned structure reduces the package procedures and saves raw materials.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.