WO1999050596A2

WO1999050596A2 - Illumination device for generating non-symmetric light beam, optical lens array and optical lens

Info

Publication number: WO1999050596A2
Application number: PCT/RU1999/000082
Authority: WO
Inventors: Vladimir Iliich Balashov; Alexandr Lvovich Zakgeim; Grigory Vladimirovich Itkinson; Arkady Semenovich Kobitsky; Mikhail Nikolaevich Mizerov; Yury Sergeevich Skvortsov; Mikhail Naumovich Sokolsky; Andrej Evgenievich Suetov; Vladimir Petrovich Tregub; Boris Ivanovich Utenkov
Original assignee: Otkrytoe Aktsionernoe Obschestvo Lomo
Priority date: 1998-03-26
Filing date: 1999-03-22
Publication date: 1999-10-07
Also published as: WO1999050596A3; AU3347699A; RU2137978C1

Abstract

The invention relates to illumination devices of the type used intraffic lights; to optical lense arrays for use in devices and systems of this and other types, and to optical lens to be used separately on as elements of such arrays. The lens of the invention is able to deviate a part of a light beam at an oblique angle to its optical axis along which the main part of the beam propagates. This effect is achieved by forming at least one side of the lens as a Fresnel surface combined from at least two zones with mutually different set of optical characteristics. Various embodiments of the novel lens can be produced by forming its other side as a conventional cylindrical Fresnel surface of a combination of several conventional cylindrical surfaces with their generatrixes made parallel or perpendicular to the direction of mutual shift of zones at the first lens side. A plurality of lenses according to the same or different embodiments of the invention can be arranged in arrays which also are capable to deviate a part of the light beam in a required direction off its main axis and thus to generate non-symmetric distribution of light at least in one plane of light propagation. The illumination device of the invention employs an array of powerful light diodes (100) and two lens arrays (200, 300), acting as condenser and diffuser. The first one of said arrays functions as a condenser, with each row of of condenser lens corresponding to a certain row of the diodes. The second lens array is as a diffuser. At least one of these arrays is formed by lenses having at least one combined Fresnel surface, and both arrays may be formed as a monolithic condensing/diffusing unit.

Description

ILLUMINATION DEVICE FOR GENERATING NON-SYMMETRIC LIGHT BEAM, OPTICAL LENS ARRAY AND OPTICAL LENS

Field of the invention The present invention relates to optical systems and in particular to illumination devices.

It has been developed primarily for use with stationary signalling lights for traffic control and will be described with references to this application. The present invention however is not limited to this particular use and may be also employed in warning lights for cars, trucks, tractors, boats and other vehicles, as well as in other optical systems designed for illuminating purposes.

Background of the invention

The function of illumination devices in stationary traffic signalling lights is to project a beam of light to be perceived by observers, such as drivers and/or pedestrians, who are moving freely at the ground level, that is below the level of traffic lights. Correspondingly, while it is desirable in a general case to obtain a symmetric distribution of the light beam radiated by the traffic lights in horizontal plane, similar distribution of light in vertical plane would lead to losses of part of the beam for observation. FIG. 1 illustrates requirements for angular distribution of light from such devices established by The Russian State Standard No. 25695-91 "Traffic Lights. Types and Main Specifications". As shown by FIG. 1A, 99% of light energy generated by the illumination device in the horizontal plane must be symmetrically distributed inside an angle of ±20° measured from a beam axis. At the same time it is required, as shown by FIG. 1B, to minimize a portion of light beam propagating upwards from the horizontal plane, while directing about 25% of the light beam downwards, at a specified small angle, e.g. from 0° to -8° to the horizontal plane. Such redistribution of light in the vertical plane results in that the angular spread of the light beam in the vertical plane must be substantially (at least 2 times) more narrow than in the horizontal plane.

While traffic lights of other types, e.g. used on railroads, may use different specific distributions of light beams, the desired characteristic of a symmetric distribution of light in the first (e.g. horizontal) plane combined with a narrow and non-symmetric distribution in the second (e.g. vertical) plane will be applicable to most of these devices.

A diversity of illumination systems for use with traffic lights have been developed. In such prior art systems, disclosed for example in the Russian Author's Certificate No. 1,494,025 or the U.S. Patent No. 5,365,418, a lamp equipped with appropriate filter(s) and optical components, such as lenses and reflectors is widely employed as a light source. Use of lamps as a light source results in low reliability, high energy consumption, limited lifetime and difficulties in achieving the required distribution of light energy.

To overcome these problems, it was proposed to employ arrays of powerful light- emitting diodes (LED) instead of lamps as light sources for traffic lights. Angular distribution of light radiated from a typical LED suitable for such application is presented in FIG. 2. Comparison of FIG. 2 with FIG. 1A and especially with FIG. 2B makes it evident that appropriate optical components must be employed in the illumination device to transform the distribution of light represented in FIG. 2 into the desired distributions shown in FIG 1.

Japan Patent Application No. 3-6601 discloses an example of an illumination device comprising, in addition to a LED array, a plurality of condenser lenses forming the first lens array and an external diffuser formed by the second lens array. Simple spherical lenses are used in both lens arrays, and each LED is located on an optical axis of the corresponding condenser lens, in the front focal plane thereof. This means that the number of condenser lenses in the first lens array is equal to the total number of LEDs; number of lens in the second lens array substantially exceeds that of the first array.

Lenses of both lens arrays in the prior art system are arranged in mutually parallel rows, and each of these arrays may be formed as a single optical component. Alternatively, both arrays may be combined into a single condensing/diffusing unit with surfaces of the condenser lenses formed at its inner side and surfaces of the diffuser lenses formed at its outer side.

Because only spherical lenses are employed in this prior art system, it evidently cannot provide a beam of light with a non-symmetric distribution in a specified plane. That is why implementation of this system in traffic control devices will lead to large losses of light propagating upwards in the vertical plane. In addition to conventional spherical lenses, lenses of other types, namely cylindrical lenses and Fresnel lenses are also finding use in various illumination devices as described, for example, in the U.S. Patents No. 4,567551, No. 5,353,211 and No. 5,365,418. Most frequently used Fresnel lenses with concentric grooves, or Fresnel facets are axisymmetric. For that reason they function precisely as conventional spherical lenses and evidently cannot provide non-symmetric distribution of the light beam. That is for conventional cylindrical lenses and cylindrical Fresnel lenses, they effectively serve the purpose of obtaining different angle distributions of light in two mutually perpendicular planes, containing lens optical axis. However, because such lens are symmetric in relation to both these planes, they are also unsuitable for producing non-symmetric distribution of the light beam in any of these planes. Summary of the invention

It is therefore the primary object of the present invention to provide an illumination device that overcomes or ameliorates the disadvantages of prior art devices in generating a light beam suitable for use in traffic lights. A more specific object of this invention is to provide an improved illumination device of the type employed in the traffic lights for generating a light beam with the first, symmetric distribution of light energy in the first (horizontal) plane and the second, preferably non- symmetric distribution in the second (vertical) plane.

One more object of the present invention is to provide an optical lens array that is capable to transform a symmetrically distributed light beam into a light beam with non- symmetric angular distribution of light energy.

A further object of the present invention is to provide an optical lens which can be employed either as an isolated optical element or as a component of a lens array for performing said transformation of a symmetrically distributed light beam into a light beam with a non-symmetric distribution.

Still another object of this invention is to provide an improved illumination device comprising, in addition to a light source constituted by an array of light-emitting diodes, two optical lens arrays designed, in accordance with teachings of the present invention, from a plurality of lenses, at least part of which are formed in accordance with teachings of the present invention.

According to the first aspect of this invention, in order to accomplish these and other objects which will become apparent from the detailed description of the preferred embodiments of the present invention, there is provided an illumination device generating a light beam with wider angular spread in the first, preferably horizontal, plane and a narrower angular spread in the second, preferably vertical plane, perpendicular to said first plane, said system comprising: a light source formed by an array of light-emitting diodes (LEDs) located in a third plane, substantially perpendicular to said first plane and to said second plane; a condenser comprising a plurality of condenser lenses forming a first optical lens array and having their front focal surfaces substantially coinciding with said third plane; and a diffuser located behind said condenser in the direction of propagation of said light beam, said diffuser comprising a plurality of lenses forming a second optical lens array.

Both LEDs and condenser lenses are preferably arranged in rows substantially parallel to the first (horizontal) plane, while each of said light-emitting diodes is located on an optical axis of one of said condenser lenses It is preferred that the first and the second lens arrays forming the condenser and the diffuser are made according to preferred embodiments of the lens array of the present invention described below.

It is also preferred that some of condenser lenses of the first lens array and of the second lens array are formed according to preferred embodiments of the optical lens of the present invention described below.

According to the second aspect of the present invention there is provided an optical lens array which may be employed in various illumination devices and in particular as the second lens array which functions as a diffuser in various preferred embodiments of the illumination system in accordance to the present invention. In some of these embodiments the diffuser comprises conventional cylindrical lenses. In these embodiments cylindrical surfaces of said cylindrical lenses are formed on an outer (rear) side of said diffuser, and generatrixes of said cylindrical surfaces are substantially parallel to the second (vertical) plane. In the preferred embodiments of the present invention distances between optical axes of adjacent cylindrical lenses with vertical generatrixes or facets are selected to be substantially, preferably 3 to 6 times less than a minimal distance between adjacent light- emitting diodes in a row of light-emitting diodes.

In other preferred embodiments of the invention conventional cylindrical surfaces of the diffuser are replaced with cylindrical Fresnel surfaces with grooves, or stepwise Fresnel facets oriented substantially parallel to said second plane.

According to several preferred embodiments of the present invention cylindrical Fresnel surfaces with facets parallel to the first, horizontal plane may be also used in the first and/or the second lens array.

Both lens arrays employed in the illumination system of the present invention may be combined into a single lens array functioning as a condensing/diffusing unit with surfaces of condenser lenses formed at its inner (front) side and cylindrical surfaces of diffuser lenses formed at its outer (rear) side. In some particular embodiments the inner side of such condensing/diffusing unit may be formed as a plurality of cylindrical Fresnel surfaces. All embodiments of the present invention employing a single condensing/diffusing unit, even though they are somewhat more difficult to manufacture, possess an important advantage of saving more light generated by the light source by minimizing the number of optical surfaces through which the light beam propagates. Because loss of light at each optical surface constitutes, due to reflection, at least 5% of the light flux, this advantage may become important in some applications of the present invention. According to the third aspect of the present invention there is provided an optical lens which may be employed either as an isolated optical element or as a component of the first or the second lens array of the invention.

The important feature of the lens in accordance with the present invention is that one side thereof is formed as a spherical or as a cylindrical Fresnel surface, while the opposite side of the lens may be formed either as a cylindrical Fresnel surface or as a group of conventional cylindrical surfaces. Composed in this way the lens of the present invention acts essentially as a combination of a spherical or cylindrical Fresnel lens with several conventional cylindrical lenses or with another Fresnel lens. As it is known to those skilled in the art, a Fresnel lens is one which uses piecewise discontinuous portions, or stepwise Fresnel facets, of relatively thin material to approximate the optical characteristics of a much thicker conventional lens of equal power. It provides the ability to achieve a high optical power without the physical bulk or necessary expense of using a very thick high-powered lens. Besides, Fresnel lenses have low aberrations in comparison to conventional lenses and they are easier to manufacture than aspherical lenses of the same low aberration level.

Another important feature of the lens of the present invention is that one or each Fresnel surface formed thereon may comprise a combination of at least two zones with different set of optical characteristics. In the frame of the present invention the expression "different set of optical characteristics" means that zones composing a combined Fresnel surface differ from each other at least by their focal distances or by position of their optical axes. When the lens of the invention is used as a part or a component of an illumination system generating a beam of light with non-symmetric distribution, at least in one plane, it is preferred that different zones of a combined Fresnel surface shall have different areas, with one zone having an area which is substantially, preferably not less than 2 times, larger than the area of any other zone of the same surface. In embodiments employing the optical lens or lenses with combined spherical Fresnel surface the said largest zone is preferably arranged around a center of said surface; and at least one zone of a lesser area is shifted in relation to the largest zone of the same combined surface in the direction substantially parallel to a plane in which non-symmetric light distribution must be produced.

It will be apparent to those skilled in the art that by varying the number of zones constituting combined Fresnel surface or surfaces of a single lens, relative sizes and positions of these zones, as well as their focal distances, it becomes possible to modify substantially the distribution of light in the horizontal and/or vertical planes. Additional capabilities for obtaining a desired distribution of a light beam can be achieved by combining lenses with different characteristics into a single lens array or into two lens arrays functioning as the condenser and the diffuser.

Brief description of the drawings

Other novel features of the present invention and advantages obtained through its use may be best understood by reference to the following detailed description taken in connection with the accompanying drawings, where like numerals represent similar components, in which:

FIG. 1 and 1B represent in a simplified graphical form the desired distribution of light generated by a traffic light illumination system in the horizontal plane and the vertical plane correspondingly.

FIG. 2 represents in a simplified graphical form a distribution of light generated by a typical powerful light-emitting diode.

FIG. 3 is a much simplified perspective view of the first embodiment of the illumination system which uses conventional cylindrical lenses in the diffuser. FIG. 4 shows an arrangement of condenser lenses for use with a specific sample of a traffic light.

FIG. 5 shows ray paths for a light beam generated by a single LED in horizontal and vertical planes when spherical Fresnel surfaces are employed to provide condenser lenses forming the first lens array. FIG. 6 shows similar ray paths in the horizontal and vertical planes when both lens arrays are combined into the condensing/diffusing unit.

FIG. 7 shows a front view, from the side of the LED array, of a condenser lens with a combined spherical Fresnel surface consisting of two zones.

FIG. 8 and 9 shows ray paths in the vertical plane through the zones of the condenser lens of FIG. 7 with correspondingly the largest and a smaller zone areas.

FIG. 10 shows ray paths in the horizontal plane through the condenser lens of FIG. 7.

FIG. 11 and 12 show ray paths correspondingly in the vertical and horizontal planes for an embodiment of the illumination system with cylindrical Fresnel surfaces formed on the inner side of the diffuser. FIG. 13 and 14 show ray paths correspondingly in the vertical and horizontal planes for an embodiment of the illumination system with the first lens array composed by Fresnel lenses while the diffuser is formed with the cylindrical Fresnel surfaces on both its inner and outer sides.

FIG. 15 and 16 show ray paths correspondingly in the vertical and horizontal planes for an embodiment of the illumination system with the combined cylindrical Fresnel surfaces on the outer side of the diffuser. FIG. 17 and 18 show ray paths correspondingly in the vertical and horizontal planes for an embodiment of the illumination system with two lens array combined into a condensing/diffusing unit having combined cylindrical Fresnel surfaces on both its inner and outer sides.

Detailed description of the preferred embodiments

For purposes of easier understanding, all embodiments of the present invention illustrated by drawings correspond to its use in traffic lights and similar signalling devices for traffic control. As noted above, devices of this type must provide a relatively broad distribution of the generated light beam in the first, horizontal plane and a relatively narrow distribution of the light beam in the second, vertical plane. However, as must be apparent to those skilled in the art, the described embodiments do not in any way limit the scope of possible applications of the illumination system under the present invention. For example, the choice of the horizontal plane as the one corresponding to the more broad distribution of the light beam must be considered as arbitrary. In addition, the term "light" widely used throughout the present specifications and appended claims must be regarded as encompassing not only visual spectral range, but also infrared and ultraviolet ranges.

Referring now to the drawings, and first to FIG. 3, 100 denotes generally a light source composed by an array of light-emitting diodes, or LEDs 1. Depending on specific field of use of a system comprising the illumination device of the present invention, the array 100 may include LEDs with similar or different characteristics. The total number of LEDs in the array is determined jointly by the intended use of the device and characteristics of LEDs. For example, about 150 LEDs of average radiated power of 5 mW may be required to create a red section of a traffic light with a diameter of 200 mm, while the number of LEDs required for a green section of the same diameter will be several times less.

To give a general picture of the illumination system of the invention, only several LEDs out of a plurality of LEDs composing the array 100 are shown in FIG. 3. As can be seen, all LEDs of the array are located in a vertical plane (designated by P) which is oriented perpendicular to both the first (horizontal) and the second (vertical) sections of light beams radiated by each LED.

The second main part of the illumination system is constituted by the condenser 200 which is composed by the first lens array 210 of condenser lenses 2. In the simplest case presented in FIG. 3, all lenses 2 of the lens array 210 have the same optical characteristics, and are located in the same vertical plane which is parallel to the plane P. The distance between this plane and plane P is selected in such a way that front focal surfaces of all condenser lenses 2 coincide with the plane P where LEDs are located. Each LED is placed on the optical axis 0₂ of the condenser lens 2 corresponding to this LED. The total number of condenser lenses in the first lens array 210 evidently equals the total number of LEDs 1 in the array 100, and a configuration of the lens array 200 closely follows a configuration of the LEDs array. As can be seen from FIG. 3, LEDs 1 and condenser lenses 2 are preferably arranged in rows 1-a, 1-b, ... 1n and 2-a, 2-b,... 2n correspondingly, which rows are substantially parallel to each other and to the horizontal plane.

FIG. 4 illustrates an arrangement of hexagonal condenser lenses 2 forming the lens array 210 for use with a specific embodiment of the traffic light device. This example makes it clear that the configuration of the lens array 210 (which repeats the configuration of the LED array) is determined by a character of the illumination system and its field of use. For example, it can be seen that the number of condenser lens 2 in a row may substantially differ from row to row of the lens array; adjacent rows of condenser lenses may be mutually shifted in the horizontal direction; in some cases the rows of condenser lenses may be oriented vertically instead of horizontally or be slanted. The third main part of the illumination system is the diffuser 300 composed by the second lens array 310 which is located behind, or rearward from the condenser 200 as seen in the direction of propagation of light beams radiated by LEDs array 100. In the embodiment illustrated by FIG. 3 the second lens array 310 consists of a plurality of cylindrical lenses 3. The inner, or front side 31 of the lens array 310 of the condenser 200 may be made flat, while cylindrical surfaces 36 of the cylindrical lenses 3 are formed on the outer side 32 of the lens array 310.

As shown in FIG. 3, generatrixes of the cylindrical surfaces 36 are oriented substantially parallel to the vertical plane, while in the horizontal direction these cylindrical surfaces 36 are very closely spaced, so that the outer side 32 of the second lens array 310 is completely filled by them. The number of cylindrical lenses 3 corresponding to one LED 1 in each row of LEDs array 100 is determined by required characteristics of the illumination system. By increasing this number, more smooth distribution of light exiting the illumination system can be obtained, and lenses of lesser thickness can be employed, with trade-off consisting in increase in manufacturing costs. For typical uses in a traffic light it is recommended to employ 3 to 6 cylindrical lenses 3 per each LED 1 (and consequently per each condenser lens 2) in each row. In other words, a distance between vertical axes of the cylindrical surfaces 36 (or, equivalent^, between optical axes of adjacent cylindrical lenses 3) are selected to be 3 to 6 times less than a minimal distance between adjacent LEDs in any row of LEDs and correspondingly 3 to 6 times less than a minimal distance between optical axes O₂ of adjacent lenses 2 in a row of condenser lenses. It is obvious that any real illumination system implementing the present invention, in addition to described parts 100, 200 and 300, must also include such parts as a housing to contain and support all optical components, appropriate fixing means to secure various parts in their respective places inside the housing, a power source for supplying the LEDs with electric energy, switching means for switching the LEDs on and off, etc. However, all such parts employed in the illumination device of the invention may be standard, described in a number of publicly available documents, including those mentioned above, and so are well known to all those skilled in the art. For that reason and for the purpose of simplification of this description of the present invention all such parts and components will be omitted from further discussion.

In some of the embodiments of the illumination system one of the surfaces of at least some of the condenser lenses 2 of the first lens array 210 is formed as a Fresnel surface 6. As mentioned above and shown in FIG. 5 for one optical lens 2 in much simplified form and not to scale, such Fresnel surface consists of a plurality of discontinuous portions, or Fresnel facets, or grooves. Each of these facets in cross-section by a tangential plane has a shape approximating a right-angle triangle with a hypotenuse slanted at an angle determined by the Fresnel equation, well known to those skilled in the art. As can be seen from FIG. 5, lens 2 is preferably made with concentric Fresnel facets and therefore forms a usual Fresnel lens which is optically equivalent to a conventional spherical lens. To distinguish a Fresnel surface with concentric facets from a Fresnel surface with rectilinear grooves, the former will be called hereinbelow a spherical Fresnel surface. Because the rules of calculating optical characteristics of such Fresnel surfaces (i.e. angular and linear parameters of their facets) are well known and described in a number of textbooks on optics, they will not be discussed here. Comparing ray paths in horizontal and vertical planes shown in FIG. 5 for optical beam radiated by the LED 1 , it can be easily seen that by use of Fresnel lenses 2 in the first lens array 210 in combination with cylindrical lens 3 in the second array 300 it is possible to obtain substantially different distribution of light in the horizontal and vertical planes because vertically oriented cylindrical lenses 3 increase spread angle of the light beam only in the horizontal plane.

As schematically illustrated in FIG. 6, in order to decrease the number of optical parts and in this way to decrease optical losses due to reflection, both lens arrays 210 and 310 may be combined into the condensing/diffusing unit 400. A plurality of spherical Fresnel surfaces 6 (only one of these surfaces is represented in FIG. 6) are patterned on the inner side 41 of the condensing/diffusing unit 400, that is on the side turned towards the LEDs array 100. The surfaces 6 form Fresnel lenses 2a, and the plurality of spherical Fresnel lenses 2a form the first lens array 210 with exactly the same configuration as that of the array of FIG. 3. The opposite, exit side 42 of the condensing/diffusing unit 400 is formed exactly as the outer side of the diffuser 3, by cylindrical surfaces 36 corresponding to cylindrical lenses 3 constituting the second lens array 310. It must be evident from the above description of the embodiments illustrated by FIGS.

5 and 6 that, by selecting various combinations of optical characteristics for lenses forming each of the two optical lens arrays, it is possible to vary in rather large range parameters of distribution of the light beam exiting the illumination system, so as to make this distribution as near as possible to the required one. However, the above-described embodiments are limited to distributions which are symmetric in the vertical plane.

The embodiment illustrated by FIGS. 7-10 is free from such limitation. The main distinctive feature of the illumination system of this embodiment is that each of at least some of spherical Fresnel surfaces 6a formed on the entrance side 41 of the condensing/diffusing unit 400 are made as a combination of at least two zones 62a and 63a with mutually offset optical axes (for clarity, only one of lenses 6a from the first lens array is shown in FIGS 7-10). These zones 62a and 63a function as two Fresnel lenses with shifted, or mismatched optical axes 0₆₂, 0₆3 (positions of these optical axes coincide in FIG. 7 with centers of each zone). Relation between areas of such zones, as well as a size of the shift between their optical axes are dictated by characteristics of the desired distribution of the light beam. As described above with reference to FIG. 1 , in typical case of non-symmetric distribution of light radiated by illumination system of a traffic light located above the level of observers, the main part of light energy in the vertical section of the light beam must be distributed symmetrically relative to the horizontal direction, while a substantially smaller part of the beam must be directed downwards at an oblique angle of 0 ° - 8°. Such distribution may be achieved with the embodiment of FIGS. 7-10 if one of the zones composing each combined spherical Fresnel surface 6a, for example zone 62a, has an area substantially larger than the area of the second zone 63b or of any other zone composing the same Fresnel surface. In order to distribute the light beam symmetrically in relation to the horizontal direction the largest zone 62a must be arranged, as shown in FIG. 7, around a center of the combined spherical Fresnel surface 6a. Relative sizes of zones composing the spherical Fresnel surface are determined by a share of light to be deviated from the main light beam. Turning again to the traffic light example, the part of the beam to be directed downwards must correspond to about 25% of the total light energy exiting the illumination system. It means that the ratio of areas of the zones 62a and 63a must correspond to 4 : 1. In general this ratio is recommended to be not less than 2 : 1. The direction of the shift of the position of the smaller zone 63a in relation to the largest zone 62a must correspond to the required direction of deviation of the part of the light beam. The case of traffic lights corresponds to downward shift of the zone 63a. The value p of such shift can be calculated from the simple equation: p = f χ sinα, (1) where f is a focal length of the condenser lens 2a; α is the angle of deviation of deviating part of the light beam.

Evidently, in case of traffic lights optimal value of α must be determined by the height of the location of this signalling device above the observers' level. The above-mentioned Russian State Standard establish the required value of α to be equal to -8°.

Distinctive feature of embodiments shown in FIGS. 11 to 16 consists in that a Fresnel surfaces are formed at least on the outer side of the diffuser 300a. In marked difference from the spherical Fresnel surface shown in FIGS. 5 to 10 the Fresnel surfaces of the diffuser 300a comprise not concentric, but rectilinear Fresnel facets 81 or 82 with cross-section in the form of a right-angle triangle with a hypotenuse slanted at an angle determined by the Fresnel equation (see for example FIGS. 15 and 16). Fresnel surface of this type is optically equivalent to a conventional cylindrical lens with a generatrix parallel to Fresnel facets. For that reason this kind of Fresnel surface will be called hereinbelow a cylindrical Fresnel surface. An optical element with a cylindrical Fresnel surface constitutes a cylindrical Fresnel lens.

Advantages of cylindrical Fresnel lenses over conventional cylindrical lenses are similar to the advantages of spherical Fresnel lenses over conventional spherical lenses which have been already discussed above. Besides, cylindrical Fresnel surfaces can be conveniently formed by moulding or by similar technologies which make their use economically attractive.

Use of cylindrical Fresnel surfaces on one or both sides of the diffuser 300a is especially recommended when distances between adjacent LEDs are relatively large, that is when the total number of LEDs is relatively small (which is typical for a green section of a traffic light). Spherical Fresnel surfaces on the contrary are advantageous in situations when LEDs are more closely packed (which is typical for a red section of a traffic light). in accordance with the present invention Fresnel facets of the cylindrical Fresnel surfaces may be oriented horizontally (as are facets 81 in FIGS. 11, 13 and 15), for shaping the light beam in the vertical plane, or vertically (as facets 82 in FIGS. 14 or 16) for shaping the light beam in the horizontal plane. In the embodiment of the illumination system schematically shown in FIGS. 11 and 12 the first lens array is composed by the condenser lenses 2 similar to those shown in FIG. 5 (only one lens 2 is shown for simplicity), while cylindrical lenses 3 formed by cylindrical surfaces 36 on the outer side of the diffuser 310 are similar to lenses 3 also shown in FIG. 5. Cylindrical Fresnel surfaces 8a in this embodiment are formed on the inner side 31 of the diffuser 300 (these surfaces will be called internal cylindrical Fresnel surfaces to distinguish them from other surfaces of the same kind). Facets 81 of the surfaces 8a are oriented horizontally, that is parallel to the rows of the condenser lenses 2 and the LEDs 1 , and each cylindrical Fresnel surface 8a corresponds to a different row of the condenser lenses 2. At least some of Fresnel surfaces 8a are formed, similar to Fresnel surface shown in FIGS. 7 to 10, as a combination of two zones 83, 84 with different focal distances. The combined cylindrical Fresnel surfaces 8a are employed in the embodiment illustrated in FIGS. 11 and 12 precisely for the same purpose as the combined spherical Fresnel surfaces 6a in the embodiment of FIGS. 7 to 10, that is to obtain non-symmetric distribution of light radiated by the LEDs (only one of which is represented in FIGS. 11 , 12) in the vertical plane. Consequently it is recommended that one zone of each combined cylindrical Fresnel surface (for example zone 84) shall have an area which is substantially (in general case at least 2 times) larger than an area of the other, smaller zone 83 of the same combined surface 8a (or any other zone if there are more than two zones). Zones 84 and 83 are shifted relative to each other in the vertical plane, that is in the plane in which it is desired to obtain non- symmetric distribution of light energy. However, in difference to employment of the combined spherical Fresnel surfaces, optical axes of both zones 84, 83 constituting the same cylindrical Fresnel surface 8a are not mutually shifted, but coincide with an optical axis of the cylindrical Fresnel surface as a whole. At the same time, these zones 84, 83 have different focal distances f^, fβ₃. As will be explained below, the following relationship (2) must take place: f₈₃ < f₈₄. (2)

Focal distance of any cylindrical Fresnel surface is determined by a value of the radius R of a hypotenuse of triangle Fresnel facets as described by the following equation (3): f = (n - 1), (3) where n is refraction coefficient for a material of a Fresnel lens.

It means that zones with different focal distances can be provided on combined cylindrical Fresnel surfaces by selecting appropriately different values of R.

In the embodiment schematically illustrated by FIGS. 13 and 14 Fresnel surfaces of two different types are also used. Spherical Fresnel surfaces 81 are again employed for forming the condenser lenses 2a of the first lens array 210. The internal cylindrical Fresnel surfaces with the horizontal facets are formed on the inner side 31 of the diffuser 300b with the purpose of obtaining the required angular distribution in the vertical plane. If this required distribution is non-symmetric, then, similar to preceding embodiment, the internal cylindrical Fresnel surfaces are formed as combinations of two zones 84, 83 having different areas and with the largest zone 84 having the largest focal distance. The external cylindrical Fresnel surfaces 8b with vertically oriented facets 82 are formed on the outer, or rear side 32 of the diffuser 300b with the purpose to achieve required distribution of light in the horizontal plane. In other words, the function of each of the Fresnel surfaces 8b is precisely the same as that of the group of cylindrical surfaces 36 shown in FIGS. 3 to 12 as matched to one LED 1 in a row. As explained above, in the case of traffic lights the angular spread in the horizontal plane is required to be substantially larger than the corresponding angular spread in the vertical plane. It means that the focal distances f_8b of the external cylindrical Fresnel surfaces 8b must be made substantially (e.g. 2 times or more) shorter than the focal distances of any zone 84, 83 of cylindrical Fresnel surfaces 8a with horizontally oriented facets. Such relationship between focal distances f₈b, f₈₃, fs is in much simplified (not to scale) form illustrated by FIGS. 13 and 14. A plurality of cylindrical Fresnel lenses formed by cylindrical Fresnel surfaces 8a, 8b on both sides of the diffuser 300b corresponds to the second lens array 310b of the illumination system of this embodiment.

In the embodiment illustrated by FIGS. 15 and 16 the first lens array may be formed either by the conventional spherical lenses 2b or by the Fresnel lenses with the spherical Fresnel surface similar to the surface 6 shown in the simplified form in FIG. 5. The distinctive feature of this embodiment is that a part of external cylindrical Fresnel surfaces 8c formed on the rear side 32 of the diffuser 300c have horizontally oriented facets 85 (as shown in FIG. 15), while the remaining part of these Fresnel surfaces have vertically oriented facets 86 (see FIG. 16). Similar to embodiments shown in FIGS. 11 to 14, Fresnel surfaces 8c with horizontal facets may be formed as combinations of two zones with different focal distances, similar to zones 83 and 84 shown in FIGS. 11 and 12. The cylindrical Fresnel surfaces 8c with vertically oriented grooves 86 serve, similar to surfaces 8b of the preceding embodiment, to shape the light beam in the horizontal plane. The inner, or front side 31 of the diffuser 300c in this embodiment may be made simply as a flat plane.

In the embodiment illustrated by FIGS. 17 and 18 the condenser and the diffuser are combined into the condensing/diffusing unit 400b similar to the condensing/diffusing unit presented in FIGS. 8 to 10. However, in the embodiment of FIGS. 17, 18 the condenser lenses constituting the first lens array are formed using internal cylindrical Fresnel surfaces with front focal planes coinciding with the third plane P (see FIG. 3) in which the LEDs 1 of the LEDs array 100 are located (only one of these LEDs is shown for simplicity). Some of the Fresnel surfaces forming the first lens array have horizontally oriented facets 85 (see FIG. 17), while the remaining surfaces have vertically oriented facets 86 (as shown in FIG. 18). Each LED 1 is matched to a pair of cylindrical Fresnel surfaces, with one Fresnel surface of this pair having the horizontal facets and so serving to collimate the partial light beam passing through it in the vertical plane (as shown in FIG. 17), while the other Fresnel surface with the vertical facets collimates the partial light beam passing through it in the horizontal plane (as shown in FIG. 18).

The second lens array 310 in this embodiment is constituted by a plurality of external cylindrical Fresnel surfaces formed on the outer side 32 of the condensing/diffusing unit 400b. As can be seen, the structure and, correspondingly, the functions of the second lens array 310 in this embodiment are similar to the second lens array of the preceding embodiment shown in FIGS. 13 and 14, so these functions will not be described in detail here. This embodiment makes it possible to minimize the number of optical components when the light source uses limited number of LEDs, as it is for example the case with the green section of the traffic light.

Now the general principle of functioning of the illumination system according to the present invention will be described. As illustrated by FIG. 2, LEDs 1 emit an axisymmetric beam of light. As was explained above, such beam does not satisfy requirements of various illumination devices, for example those employed in traffic or other signalling lights, so that appropriate transformation of the beam's shape is required. The first stage of this transformation is effected by the condenser 200. As can be seen from FIG. 5, each of condenser lenses 2 have its front focal point aligned with a matched LED 1 and consequently the first lens array 210 of lenses 2 as a whole produce the parallel light beam LF which impinges on the diffuser 300. The diffuser modifies the distribution of energy in this light beam LF in the horizontal and/or the vertical planes, according to the required shape of the light beam at the exit of the illumination system. For example, it must be evident to those skilled in the art that by using embodiments described with reference to FIGS. 3 to 5 and by composing each array with lenses of different types and features, it is possible to vary in rather large range parameters of distribution of the exiting light beam, for example to obtain substantially different distribution of light energy in the vertical and horizontal planes.

As can be seen from FIGS. 5 to 10, a required angular spread of light in the horizontal plane independently of its distribution in the vertical plane may be achieved by selecting appropriate focal distances of cylindrical lens 3 of the second lens array 310 in the diffuser 300 because these focal lengths determine the angle α_h characterizing the spread of light in the horizontal plane. However, as mentioned above, by employing arrangement of FIGS. 3 to 6 it is impossible to achieve the object of obtaining a non-symmetric distribution of light in one of the planes passing through an axis of the beam's propagation, and in particular to redirect a part of the beam downwards, as required in traffic lights. This object may be however achieved in accordance with the invention by using Fresnel surfaces formed as combinations of zones characterized by different sets of optical characteristics.

As can be best seen from FIGS. 9 and 10, when combined spherical Fresnel surface 6a formed according to the present invention is used, its largest zone 62a which is arranged around the center of the surface 6a (as shown in FIG. 7) functions in just the same way as the condenser lens 2 of FIGS. 5 or 6, that is it shapes the light beam radiated by the LED 1 into the parallel beam LF. At the same time the second, smaller zone 63a functions as an off- axis lens which deviates (as best may be seen in FIG. 9) a part of the beam impinging on the surface 6a by the angle α in the downward direction coinciding with the direction of the shift of the zone 63a in relation to the largest zone 62a. As mentioned above, the cylindrical lenses 3 constituting the second lens array 310 shape the light beam passing through them only in the horizontal plane, so they do not influence this downward deviation of a partial beam which passes through the smaller zones 63a of the condenser lenses. As a result the desired distributions of light energy may be achieved in both the horizontal and vertical planes. The cylindrical Fresnel surfaces 8a, 8b, 8c used in the embodiments illustrated by

FIGS. 11 to 18 function, depending on orientation of their facets, as cylindrical lenses with horizontal or vertical orientation of their generatrixes. Using surfaces with the vertical facets 82 it is possible to redistribute light energy in the horizontal direction (see for example FIG. 16). In other words, cylindrical Fresnel surfaces with the vertical facets used as part of the diffuser 300b, 300c can replace cylindrical surfaces 36. Surfaces with the horizontal facets 81 are effective for redistributing light energy in the vertical direction (as shown in FIGS. 11 and 12). By combining these two types of surfaces it becomes possible to control the shape of the light beam in both directions, as illustrated by FIGS. 13 to 18.

As shown in FIGS. 11 , 13, 15 and 17, use of cylindrical Fresnel surfaces comprising at least two zones 83, 84 with different focal distances makes it possible to form two partial beams with different spread angles α-i, α₂ because the focal distances of these zones, f₈₄, f₈₃ respectively, the same as those of other optical surfaces, are inversely related to the angular spread of the partial beam which is shaped by the corresponding zone.

Turning again to already considered example of the traffic lights, the largest zone 84 must form a main part of the light beam with a symmetric angular spread of ± 3°, while the part of the light beam deviated by the zone 83 must have an angular spread of 0° to -8°. The first required angular spread being less than the second one, the following relation must be observed: f₈₃ < f₈₄. (2)

As illustrated in simplified and not to scale form by FIG. 11 or 13, the spread angle α₂ in the vertical plane of the partial light beam passing through the largest zone 84 with the longest focal length is substantially narrower than the spread angle αι of the other partial beam passing through the other zone 83 with shorter focal length.

As shown in FIGS. 7 to 10 and 13 to 18, by combining different types of Fresnel surfaces in a single optical element, it is possible to create optical lenses capable to provide not only symmetric, but also non-symmetric distribution of a light beam energy in any selected plane or in both mutually perpendicular planes along the direction of the beam's propagation. As was shown above, optical lenses made in accordance with the present invention may be easily assembled into lens arrays that may be also formed as single optical components for their effective use with arrays of light-emitting diodes to produce various illumination devices providing light beams of required shapes, including non-symmetric shapes in one or two planes.

While this invention has been illustrated and described in detail in connection with only certain embodiments, other embodiments will readily suggest themselves to those skilled in the art. For example, aspherical Fresnel surfaces may be employed instead of the spherical surfaces, zones forming combined spherical or cylindrical Fresnel surfaces may be shifted relative to each other not only in the vertical, but also in the horizontal direction or in a direction forming an oblique angle with the vertical direction. In some special cases it may become useful to combine in a single lens array Fresnel lenses having the above-described combined Fresnel surfaces with conventional Fresnel lenses or even with conventional lenses. It must therefore be understood that this application is intended to cover any such modifications, changes and substitutions of the described lens array and/or illumination system as may fall within the scope of the invention as defined by the appended claims.

Further, while it has been suggested that the above-described illumination system is particularly suitable for use with traffic lights or similar signalling devices, it should be understood that it may also be embodied in a large number of other optical devices and systems employing non-symmetric light beams, such as for example, various signalling lights employed in vehicles of all kinds and the like. It is intended that all such applications of the described or modified optical lenses, lens arrays and illumination systems fall within the scope of the appended claims.

Claims

1. An illumination device generating a light beam with wider angular spread in the first, preferably horizontal, plane and a narrower angular spread in the second, preferably vertical plane, perpendicular to said first plane, said device comprising: a light source formed by an array of light-emitting diodes located in a third plane, oriented substantially perpendicular to said first plane and to said second plane, wherein said light-emitting diodes are preferably arranged in rows substantially parallel to said first plane; a condenser comprising a plurality of condenser lenses, which condenser lenses form a first optical lens array and have their front focal surfaces substantially coinciding vvith said third plane, wherein said condenser lenses are preferably arranged in rows substantially parallel to said rows of light-emitting diodes, with each of said light-emitting diodes located on an optical axis of one of said condenser lenses; and a diffuser located behind said condenser in the direction of propagation of said light beam, said diffuser comprising a plurality of cylindrical lenses forming a second optical lens array, wherein: cylindrical surfaces of said cylindrical lenses are formed on an outer side of said diffuser, generatrixes of said cylindrical surfaces are substantially parallel to said second plane, and distances between optical axes of adjacent cylindrical lenses are substantially, preferably 3 to 6 times, less than a minimal distance between adjacent light-emitting diodes in any row of said light-emitting diodes.

2. The illumination device of claim 1 , wherein: one of the surfaces of at least some of said condenser lenses is formed as a spherical Fresnel surface; each of at least some of said spherical Fresnel surfaces is formed as a combination of at least two zones with mutually offset optical axes.

3. The illumination device of claim 2, wherein: one of said zones on each combined spherical Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of the same surface; said largest zone of said combined spherical Fresnel surface is arranged around a center of said surface; and at least one zone of the lesser area is shifted relative to said largest zone of the same combined surface in a direction substantially parallel to said second plane.

4. The illumination device of any of preceding claims, wherein: internal cylindrical Fresnel surfaces of said condenser lenses are formed on the inner side of said diffuser, with each said internal cylindrical Fresnel surface corresponding to a different row of said light-emitting diodes; stepwise Fresnel facets constituting each of said internal cylindrical Fresnel surfaces are oriented parallel to said rows of light-emitting diodes.

5. The illumination device of claim 4, wherein at least part of said internal cylindrical Fresnel surfaces are formed as a combination of at least two zones with different focal distances.

6. The illumination device of claim 5, wherein: one of said zones on each combined cylindrical Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of the same combined surface.

7. The illumination device of any claim from 1 to 3, wherein said condenser and said diffuser are formed as a combined condensing/diffusing unit with surfaces of said condenser lenses formed on its internal side and said cylindrical surfaces of said cylindrical lenses formed on its outer side.

8. An illumination device generating a light beam with wider angular spread in the first, preferably horizontal, plane and a narrower angular spread in the second, preferably vertical plane, perpendicular to said first plane, said device comprising: a light source formed by an array of light-emitting diodes located in a third plane, oriented substantially perpendicular to said first plane and to said second plane, wherein said light-emitting diodes are preferably arranged in rows substantially parallel to said first plane; a condenser comprising a plurality of condenser lenses, which condenser lenses form a first optical lens array and have their front focal surfaces substantially coinciding with said third plane, wherein said condenser lenses are preferably arranged in rows substantially parallel to said rows of light-emitting diodes; and a diffuser located behind said condenser in the direction of propagation of said light beam, said diffuser comprising a plurality of cylindrical lenses forming a second optical lens array, wherein: surfaces of said cylindrical lenses are formed on an outer side of said diffuser as external cylindrical Fresnel surfaces; stepwise Fresnel facets constituting at least a part of said external cylindrical Fresnel surfaces are oriented substantially parallel to said first plane; stepwise Fresnel facets constituting the remaining part of said external cylindrical Fresnel surfaces are oriented substantially parallel to said second plane; and each of said external cylindrical Fresnel surfaces with said Fresnel facets oriented parallel to said first plane corresponds to a different row of said light-emitting diodes.

9. The illumination device of claim 8, wherein: one of the surfaces of at least some of said condenser lenses is formed as a spherical Fresnel surface; each of at least some of said spherical Fresnel surfaces is formed as a combination of at least two zones with mutually offset optical axes; each of said light-emitting diodes is located on an optical axis of one of said spherical Fresnel surface.

10. The illumination device of claim 9, wherein: one of said zones on each combined spherical Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of the same surface.

11. The illumination device of claim 10, wherein: said largest zone of said combined spherical Fresnel surface is arranged around a center of said surface; and at least one zone of the lesser area is shifted relative to said largest zone of the same combined surface in the direction substantially parallel to said second plane.

12. The illumination device of any of claims from 8 to 11 , wherein: internal cylindrical Fresnel surfaces are formed at the inner side of said diffuser; stepwise Fresnel facets constituting at least part of said internal cylindrical Fresnel surfaces are oriented parallel to said rows of light-emitting diodes; remaining part of said internal cylindrical Fresnel surfaces are oriented perpendicular to said rows of light-emitting diodes. each of said cylindrical Fresnel surfaces with said Fresnel facets oriented parallel to said rows of light-emitting diodes corresponds to a different row of said light-emitting diodes.

13. The illumination device of claim 12, wherein said Fresnel facets of all said internal cylindrical Fresnel surfaces are oriented parallel to said rows of light-emitting diodes.

14. The illumination device of claim 12 or 13, wherein: at least part of said external cylindrical Fresnel surfaces with said Fresnel facets oriented parallel to said rows of light-emitting diodes are formed as a combination of at least two zones with different focal distances.

15. The illumination device of claim 14, wherein one of said zones on each combined cylindrical Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of the same surface; and at least one zone of the lesser area is shifted relative to said largest zone of the same combined surface in the direction substantially parallel to said second plane.

16. The illumination device of claim 12, wherein said condenser and said diffuser are formed as a combined condensing/diffusing unit with said internal cylindrical Fresnel surfaces formed at its inner side and said external cylindrical Fresnel surfaces formed at its outer side.

17. An optical lens array formed by a plurality of lenses preferably arranged in mutually parallel rows, wherein: one surface of at least a part of said lenses is formed as a spherical Fresnel surface; each of at least some of said spherical Fresnel surfaces is formed as a combination of at least two zones with mutually offset optical axes.

18. The optical lens array of claim 17 wherein one of said zones on each combined spherical Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of said surface; said largest zone of said combined spherical Fresnel surface is arranged around a center of said surface; and at least one zone of the lesser area is shifted relative to said largest zone of the same combined surface in the direction substantially parallel to said second plane.

19. The optical lens array of claim 17 or 18 wherein: the second side of said array is formed as a plurality of cylindrical surfaces of cylindrical lenses with generatrixes of said cylindrical surfaces being perpendicular to said rows; and distances between optical axes of adjacent cylindrical lenses are substantially, preferably 3 to 6 times less than a minimal distance between optical axes of adjacent spherical Fresnel surfaces in a row.

20. The optical lens array of claim 17 or 18 wherein: the second side of said array is formed as a plurality of cylindrical Fresnel surfaces; stepwise Fresnel facets of at least a part of said cylindrical Fresnel surfaces constituting the first group of said surfaces are oriented perpendicular to said rows of said spherical Fresnel surfaces.

21. The optical lens array of claim 20 wherein: at least part of said cylindrical Fresnel surfaces belonging to said first group are formed as a combination of at least two zones with different focal distances; one of said zones on each combined cylindrical Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of said surface; at least one zone of the lesser area is shifted relative to said largest zone of the same combined surface in the direction substantially perpendicular to said rows of said spherical Fresnel surfaces.

22. The optical lens array of claim 20 or 21 wherein said Fresnel facets of said cylindrical Fresnel surfaces constituting the second group of said surfaces are oriented perpendicular to said Fresnel facets of the first group of said cylindrical Fresnel surfaces.

23. An optical lens having one side thereof formed as a Fresnel surface, which surface being a combination of at least two zones with mutually different set of optical characteristics.

24. The optical lens of claim 23 wherein one of said zones on each combined Fresnel surface has an area substantially, preferably not less than 2 times, larger than the area of any other zone of said surface.

25. The optical lens of claims 23 or 24 wherein: said combined Fresnel surface is a spherical Fresnel surface; said zones of said spherical Fresnel surface have mutually offset optical axes; said largest zone of said combined spherical Fresnel surface is arranged around a center of said surface.

26. The optical lens of claim 23 or 24 wherein said combined Fresnel surface is a cylindrical Fresnel surface, with said zones having different focal distances.

27. The optical lens of any claim from 23 to 26 wherein the second side thereof opposite to said first side is formed as a cylindrical Fresnel surface.

28. The optical lens of claim 27 wherein: said cylindrical Fresnel surface of said second lens side is formed as a combination of at least two zones with different focal distances; and one of said zones has an area substantially, preferably not less than 2 times, larger than the area of any other zone of said surface.

29. The optical lens of claim 27 or 28, wherein stepwise Fresnel facets of said cylindrical Fresnel surface of the first lens side are oriented perpendicular to stepwise Fresnel facets of said cylindrical Fresnel surface of the second lens side.

30. The optical lens of claim 25 wherein: the second side thereof opposite to said first side is formed as one or more cylindrical surfaces with mutual parallel generatixes, which surfaces forming one or more cylindrical lenses; generatrixes of said cylindrical surfaces are oriented substantially parallel to a direction of a shift of a zone of the lesser area of said combined spherical Fresnel surface relative to the largest zone of said spherical Fresnel surface.