Title of invention
Bi- cylindrical lens and lens array for general illumination pattern control
FIELD OF INVENTION
The present invention relates to a the field of optics, where a ray tracing based bi-cylindrical lens and lens array model for distant area illumination pattern control is described.
BACKGROUND OF THE INVENTION
In distant surface illumination like road, indoor, industrial illumination etc., controlling of illumination distribution pattern, uniform illuminance with sharp cut-off illumination outside a required portion are very important to maintain higher co-efficient of utilization of the illumination.
A number of optical systems have been described in the prior arts to achieve uniform illumination over a predetermined surface. The illumination distribution control is limited by restricting number of freedoms in structural parameters of an optical system.
Patent number UD2008000032 discloses a lighting device which comprised of an optical system to direct light emitted from a light source on a predetermined surface. The optic members produced many elliptical light spots which illuminated the determinate surface in a rectangular stripe which comprised of many elliptical light spots. The light source and the optical system together were tilted with respect to the lighting device in order to direct the resultant light of rectangular shape towards the determinate surface. This optical system had only one degree of freedom which was tilting of the optical module, comprising of the light source, to direct the light in a direction to illuminate the predetermined surface. Hence, this system can emit light in different directions, depending on the location of the illuminating surface, but with only one single shape of the output light beam. A variety of shapes and patterns of the illumination on the surface could not be achieved here and also this type of system results in wastage of light.
Another prior art CN101105271 disclosed a lighting fixture comprised of LED, aspherical collimator lens and an array of aspherical micro lenses. This module of LED and aspherical micro lens array illuminated the road in rectangular stripe laterally along its length. The patent discloses only one shape of the light illumination pattern i.e. rectangular which is obtained. Hence, shapes other than rectangular could not be achieved.
Many lenses were also disclosed in the prior arts which had cylindrical lenses with crossed cylindrical axes. These type of cylindrical lenses had a front cylindrical surface curvature and a rear cylindrical surface curvature in such a way that surface area of the curved surface doesn't change with respect to the physical area enclosed by the length and width of the lens element. One such cylindrical lens has been described in US5973853. Cylindrical lenses of this type could not achieve a degree of freedom of operation in the axes of their front and rear cylindrical surfaces with respect to length and width of the lens element(2), (it means that the curved surface areas of the cylindrical surfaces of the lens element could not be changed).
The general state-of-art cylindrical lenses produce light beams of particular shapes for predetermined segments. These segments do not have sharp cut off boundary and hence, some of the light also falls out of the segment. Due to this, wastage of light falling on the segment occurs.

Hence, a need to introduce more degrees of freedom in cylindrical lenses to achieve a variety of illumination pattern and to have a control over this illumination arises.
Also, it is an objective of our present invention to achieve uniform illumination and to avoid as much wastage of light as is possible by creating sharp cut off illumination pattern and hence, to achieve high coefficient of utilization factor in the illuminating surface .
SUMMARY OF INVENTION
In order to achieve the above mentioned objective, a bi- cylindrical lens is developed to provide two more additional freedoms in the structural parameters of the lens. Combination of these individual lenses form a bi- cylindrical lens array which is designed ,
by Ray Tracing based geometrical modeling of the lens array
This is done in order to achieve controlled illumination distribution pattern, uniform illuminance with sharp cut-off illumination outside a required portion of a distant illumination surface. These additional freedoms are given in Front Cylindrical Axis Rotation (FAR) and Back Cylindrical Axis Rotation (BAR) with respect to length and width of the lens in the array. These rotations can be same or different with respect to each other.
Such a bi- cylindrical lens model has developed by taking an application example of segmented illuminating area with square patch wise illumination requirement. A bi- cylindrical lens array comprising of a plurality of individual bi- cylindrical lenses where a collimated beam is incident on the lens array. The diameter of the bi-cylindrical lens array base is selected as per the diameter of the collimated light beam. The dimensions of bi-cylindrical lenses in the array and the number of lenses can be selected according to uniformity in luminous flux density at the cross section of the collimated beam. Geometric ray tracing starts by taking the lens array disc axis as optical axis. Optical axis of the lens array is directed towards a center point of a segment to be illuminated, (center point of the patch, which is to be illuminated with controlled illumination). A single bi-cylindrical lens (central lens ) in the array, out of total lenses , is selected to optimize the structural parameters of the lens . Initial pre structural parameters, Front Surface Curvature (FSC), Back Surface Curvature (BSC), Front Cylindrical Axis Rotation (FAR) and Back Cylindrical Axis Rotation (BAR) with respect to the length and width of the lens in the lens array as per lens imaging analytical relations are recorded. Now the structural parameters of the cylindrical lenses can be optimized according to required illumination pattern.
To optimise the structural parameters of the lenses in the lens array for achieving uniform luminous flux on the required segment by ray tracings following steps are carried out, where the foot print of the light beam on the segment is observed with every optimised set of structural parameters. Firstly, the ray intercept points are selected on the front surface of the array lenses . Secondly, the lens array rotation (LAR) is tuned clockwise/anticlockwise according to the observed the light beam foot print. Thirdly, the other structural parameters, FSC, BSC, FAR and BAR with respect to length and width of the lens

are optimised depending on the desired shape and pattern of the illumination and location of the segment. These structural parameters are optimised in a way, that the beam foot print observed from this set of parameters conform with the required shape and pattern of the segment to be illuminated.
The structural parameters are maintained same to all the lenses in the lens array. Since each lens in the array independently fills the segment completely. Therefore, it will give uniform illuminance in the segment even with the non uniform flux distributed input beam. A single bi-cylindrical lens may not be capable of giving uniform illumination and a variety of shapes and patterns which are desired, therefore, an array of such lenses is utilised to obtain uniformity and control in the illumination patterns.
Also, in a possible embodiment of the invention, the structural parameters are different from each other for every lens Each lens produces a different shape of light beam, and the superposition of these different light beam shapes on a segment results in a particular shape and pattern of the illumination, depending on the superposition.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure- 1: Front view of the bi-cylindrical lens array disc.
Figure- 2: Expanded front view of the lenses in the array
('a' and 'b' are the length and width of the lens (4) respectively, 'c' is the gap between the lenses , and the values are taken as examples) Figure- 3 Single lens view of the lens array.
Figure-4: Angle indication of the cylindrical axis of the lens due to rotation Figure-5: Segmented illuminating surface
Figure-6: Cylindrical surface profile of the bi- cylindrical lens in the lens array with different angular rotation of cylindrical axis.
Figure-7: Front view of the bi- cylindrical lens showing the rotation of axis of cylinder
Figure-8.1 and Figure-8.2: Different views of a cylindrical surface of bi- cylindrical lens before and after rotation of cylindrical axis, for clear visual understanding. Graphs 1-5 show the foot prints of luminous flux distribution with ray tracing on the segment of surface, (the units are "mm")
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a bi-cylindrical lens (2) for controlling a distant area illumination pattern. A number of bi- cylindrical lenses(2) are grouped together to form an array(1) of bi- cylindrical lenses(2).
The bi- cylindrical lens (2) comprises of two opposite cylindrical end faces known as front cylindrical surface and back cylindrical surface, both the surfaces have their respective cylindrical axis, and these surfaces are disposed against each other in such a way that the cylindrical end faces are opposite to each other. These end faces of the lens (2) can attain any shape for e.g. convex, concave or a combination of both. The bi-cylindrical lens (2) can be monolithic in nature, i.e. it can be fabricated out of one single

piece of material. Each bi- cylindrical lenses (2) has a set of structural parameters. These parameters of the lenses (2) in the lens array(1) help in controlling the illumination pattern and uniformity in the illuminance of a predetermined segment(4) of a surface area(3) which is to be illuminated. Also shape of the illumination pattern can be controlled by these structural parameters, along with a proper alignment of this shape with the required shape of the predetermined segment(4) on the surface(3) to be illuminated. All the structural parameters are maintained same for each bi-cylindrical lens (2) in the lens array(l) to achieve uniform illuminance.
Generally, a collimated light beam is incident on the lens array(l). This light beam may have either uniform or non uniform luminous flux density at its cross sectional area. The axis of the lens array(l) disc is taken as optical axis. The optical axis of the lens array(l) directs the light beam towards the center of the illuminating segment(4), which is a distant segment on the illuminating surface(3) with respect to the point at which the lens array is mounted. This point is called as mounting point of the array(lO). The bi-cylindrical lens array(l) emits a beam of light which illuminates a predetermined segment(4) of a surface area(3). Each lens (2) produces a beam of light to illuminate this segment(4) having its own luminous flux density where each lens (2) independently illuminates the segment(4) completely with the same shape and orientation of the illumination pattern. Hence, a uniform illuminance is achieved in the segment(4). Maintaining the structural parameters of the lenses (2) in the lens array(l) at a required value depending upon the required illuminance, uniform and sharp cut-off illumination at the required segment(4) of the distant illuminating surface area(3) are achieved.
The structural parameters, which are maintained same for each bi-cylindrical lens (2) in the lens_array(l), are:
1) Front Surface Curvature (FSC) which is the radius of curvature of the front surface of one lens
2) Back Surface Curvature (BSC) which is the radius of curvature of the back surface of the lens
(3)Front Cylindrical Axis Rotation (FAR) of the bi-cylindrical lens (2) with respect to the
length and width of the lens (2).
(4) Back Cylindrical Axis Rotation (BAR) of the bi-cylindrical lens (2) with respect to
the length and width of the lens (2).
(5)Lens Array rotation (LAR) around the central axis of the lens array(l).
The above mentioned five parameters of the lens (2) can be modified to get the desired shape and pattern of the illumination for a required segment(4). The radii of curvatures control the area of the predetermined segment(4) which is to be illuminated.
The front and the back cylindrical axes of rotation control the shape and pattern of the output beam of light as per the required shape and pattern of the segment(4) to be illuminated.
The lens array rotation (LAR) around the central axis of the lens array(l) controls the illumination pattern so that the resultant light beam shape produced from the lens array(l) fits into the required shape of the segment(4)of the surface(3) to be illuminated. This means that the light beam shape which is produced from the lens array(l) is perfectly aligned with the shape of the illumination on the segment(4) of the surface(3).
Controlling all the above mentioned structural parameters of bi- cylindrical lenses (2) in the

lens array(l), uniform illumination and sharp boundary cut-off are achieved, further resulting in high coefficient of utilization factor on the illuminating surface(3). This means that the area of illuminated segment(4) will have uniform illumination and sharp boundary beyond which the light is restricted to fall. Hence, any extra light falling out of the required illuminating segment(4) and the surface area(3) can be eliminated resulting in reducing the wastage of the light.
Figure-1 shows front view of the bi-cylindrical lens array(l) disc comprising of a number of individual bi- cylindrical lenses (2). In this view, front surface of each lens (2) is visible having front surface curvatures(FSC) which can be modified according to the distance at which the segment(4) of the surface(3) has to be illuminated. These lenses leas (2) have back surface curvatures(BSC) which are at the rear of the lenses(2) , not visible in the front view.
Figure-2 shows the expanded front view of the lenses (2) in the leas array(l) in XY plane where X-axis is along the width of the lens (2) and Y-axis is along the length. For a simple explanation, only four lenses are shown. The front surface curvatures of the lenses(2) seem to be of square shape when seen from the front. Hence, the front view of the curved lenses(2) will be as shown in Figure-2. The dimensions of the cylindrical lenses (2) and the number of the lenses(2) in lens array(l) needed can be altered according to the uniformity in luminous flux density at the cross section of the collimated beam incident on the bi- cylindrical lens array(1).
Figure-3 shows a single convex bi-cylindrical lens (2) in XZ, YZ and XY planes where Z-axis is along the thickness of the cylinder and is perpendicular to the X- and Y- axes. In XZ plane, the front surface curvature of the lens (2) is shown. In YZ plane, the rear or back surface curvature of the lens(2) is shown. In XY plane, the front view of the lens(2) is shown which is of square shape.
Figure-4 shows rotation of the cylindrical axis of a lens (2) and the resultant change in the angle of the cylindrical axis (which is passing through the center of the lens (2)) with respect to the length and width of the lens (2). Consider for an example, rotation of front curvature of a lens (2) around Z-axis. In the front curvature, X-axis is along the width, Y-axis along the length and Z-axis along the thickness of the lens (2). Before rotation, the initial angle between the Y-axis and the cylindrical axis, φx, is 0° (zero degrees) which means that both of these axes are parallel to each other. Now the front cylindrical axis is rotated by a small angle around the Z-axis of the cylindrical lens (2). The cylindrical axis now makes an angle with the Y-axis, say for an example, now φX is 10° (10 degrees). This is known as Front Cylindrical axis rotation (FAR). In the similar way Back (or Rear) axis Rotation (BAR) is obtained by rotating the rear surface curvature of the lens(2). In this way, different profiles of the front and the rear surface curvatures of the bi cylindrical lenses(2) can be obtained by rotating the respective axes at different or same angles around Z-axis. The cylindrical surface profile of the lens (2) before and after rotation is shown in Figure-6. Due to this rotation, the curved surface areas of the cylindrical surfaces change and hence, different types of curved surface profiles for the bi-cylindrical lens (2) can be obtained. This results in achieving a variety of shapes of the light beam emitted from the lens (2). Therefore, the segment(4) can be uniformly illuminated with a variety of shapes and patterns. Hence, the bi- cylindrical lens (2) has a freedom of operation in its FAR and BAR along with freedom of operation in its FSC and BSC radii.

The general state-of-art cylindrical lenses do not include such rotation of the axes, hence there is no change in the curved surface area of the cylindrical surface. Therefore, a variety of shapes and pattern of the resultant light beam can not be achieved here.
A variety of shapes and patterns of the illumination can be produced by one bi- cylindrical lens array(l) which illuminates a segment(4), by rotating the cylindrical surface curvatures of the lens(2) and then super-positioning of the light beams produced by each of the lens (2) independently in the lens array(l). Every lens (2) in the lens array(l) have front and rear cylindrical surface profiles which are obtained by rotating the front and back cylindrical axes around the Z-axis of the respective lens (2) at same angles or different from each other . This means that rotation of front and back cylindrical axes with respect to Z-axis results into the change in curved surface areas of the front and back cylindrical surfaces of a lens (2). This angle of rotation can be same or different for both the axes with respect to Z-axis. As a possible variant to this, the front and rear cylindrical surfaces can also be different from each other. If each lens (2) in the lens array(l) has same structural parameters i.e. they have same FSC, BSC, FAR and BAR, then every lens(2) produces a beam of light of same shape and orientation and these light beams get superimposed on each other at the segment(4) to illuminate it with the same resultant shape. This results in uniform illumination of the segment(4) and sharp cut-off boundary of every segment(4) of the surface(3) {4} which restricts the illuminance within this boundary only and hence eliminates the wastage of light, with a high coefficient of utilization factor.
In the variant, if the curved surface profiles of bi- cylindrical lenses(2) are different from each other, then each lens (2) produces a beam of light with a particular shape which is different from the other light beams produced by the rest of the lenses (2) in the lens array(l). This means one bi- cylindrical lens array(l) produces beams of light of different shapes depending on the architecture of individual lens (2). But, super-positioning of these different beam shapes produced from a single array(l) on the segment(4), illuminates the segment(4) with a particular resultant shape which depends on how the superposition occurs.
Figure-5 shows segmented illuminating surface(3) comprising of a number of segments(4). Each of the segment is illuminated by a single bi- cylindrical lens array(l). A lens array(l) is mounted at a distance from the predetermined segment which is to be illuminated and the point at which the lens array(l) is mounted is known as mounting point (10).
Figure-7 shows the axis of bi- cylindrical lens (2) with respect to length and width of the lens (2) before and after rotation. Before rotation of the axis, Figure-7(a) shows the axis of the lens (2) as parallel to the width of the lens (2). Figure-7(b) shows the axis as inclined at an angle with respect to the length and width of the lens (2) which is due to rotation of the axis. In this case, the curved surface profile of the cylindrical surface also changes with respect to the length and width of the lens (2).
Figure-8.1 and Figure- 8.2 show more clearer views of the bi- cylindrical lens (2) of Figure-6 for visually understanding the effect of rotation of axis on the cylindrical surface profile. Fig8.1(a) shows the curved surface profile with respect to length and width of the lens (2) before the rotation of the axis of the cylindrical lens (2). After the rotation of the axis with respect to length and width of the lens(2), the curved surface profile of the cylindrical surface changes accordingly, which is shown in Figure-8.1(b).

Figure- 8.2(a) shows the curved surface profile as divided into plurality of discrete sections of the same cylindrical shape which are aligned parallel to each other. Before rotation, as shown in Figure- 8.2(a), these sections are parallel to the width of the lens (2). After the rotation of the axis of the bi- cylindrical lens (2), shown in Figure- 8.2(b), the discrete sections are inclined at angles with respect to the length and width of the lens (2) which changes the curved surface profile accordingly.
Example:
For a simple explanation, consider segment(4) patch number 70 of the illuminating surface(3), which is one of the square segment on the complete illuminating surface area(3) and has to be illuminated uniformly with sharp boundary cut-off. A collimated beam of light is incident on the bi- cylindrical lens array(l). The diameter of the lens array(l) is selected as per the diameter of the collimated source. Geometric ray tracing is initiated by taking the lens arrav(l) disc axis as the optical axis. The optical axis of lens array(l) aligned with the center of the collimated input light beam of 36mm diameter (say), is directed towards the center point of the illuminating segment(4) of patch number 70. The size of the lens (2) in the array is selected to be approximately 3.5 mm X 3.5 mm square (some are less). All the lenses(2) are of the similar dimensions. Here, a bi- cylindrical lens array(l) comprises of a total of 88 lenses(2) Considering the co-ordinate plane of the illuminating surface(3), the foot of the perpendicular on which the lens array(l) is mounted has the co-ordinate points as X=0, Y=0, Z=0 in global co-ordinate system and the lens array(l) is mounted at a point X=0, Y=0, Z=6000. This implies that the height at which the array(l) is mounted is 6 meter. Each of the 88 lenses(2) produces 1 meter X 1 meter light beam which is dependent on the structural parameters of the lens (2) taken here and each bi- cylindrical lens (2) out of the total 88 lenses in the lens array(l) independently illuminates a single segment patch(4) of 1 meter X 1 meter with the same shape and orientation of the illumination pattern, of the surface area(3). This illumination pattern in the segment(4)number 70 of lmeter X lmeter is achieved by controlling the structural parameters of the bi- cylindrical lens (2) which are denoted as follows:
Al- Front Surface Curvature(FSC) of radius of curvature, XR= 39mm convex
A2- Back Surface Curvature(BSC) of radius of curvature, YR= 26mm convex
A3- Front Cylindrical Axis Rotation (FAR) with respect to the length and width of the lens
in the lens array, XA= -18degree
A4- Back Cylindrical Axis Rotation(BAR) with respect to the length and width of the lens
in the lens array, YA= 0 degree
A5- Lens array rotation (LAR) around the axis of the lens array axis LAR=23degree
All the above mentioned values of collimated beam diameter, dimensions of the lens (2) and structural parameters are examples, and can be modified according to the shape and pattern of the illuminating segment(4) and according to the uniform illuminance of the segment(4). These structural parameters FSC, BSC, FAR and BAR are same for all the 88 lenses in the lens array(l) and the lens array(l) has to rotate according to the angle LAR around its axis. The structural parameters obtained are according to the rav tracing analysis bv observing rav illumination pattern.
Likewise, a set of above (A-1 to A-5) parameters for some more segments
21,30,41,50,58,59,60, has tabulated as shown below to understand the complete idea behind
the shaping of the illumination distribution on the plane.

Table:1
(Table Removed)
Referring to the graphs, graph 1 shows the illumination pattern on segment(4) with initial pre-structural parameters of the bi- cylindrical lens(2) , selection of which depends on the designer. First, the LAR is tuned and selected by rotating the bi- cylindrical lens array disc(l) around its central axis. Then, the structural parameters FAR, BAR, BSC and FSC are gradually optimized according to the illumination pattern obtained for the first set of parameters and according to what resultant pattern is required finally. During optimizing the structural parameters of the lenses, the various illumination patterns obtained by various sets of structural parameters are recorded via these graphs. Graph-5 shows the ideal illumination pattern obtained by an ideal set of structural parameters of the lenses (2) and hence the lens array(l). Graph 2-4 shows the intermediate patterns obtained while optimizing the structural parameters and achieving the desired illumination pattern, shown in graph-5, from the one obtained from the pre-structural parameters, shown in graph-1.
In Graphs 1-5,
> X-axis of the graph (horizontal) is X-axis of the illuminating surface
> Y-axis of the graph (vertical) is Y-axis of the illuminating surface
> Center point of the segment(4) is X=9500, Y=4000 in coordinate axis of the illuminating surface(3)
> The portion of the segment area to be illuminated for the segment(4) in the coordinate plane of the illuminating surface(3) is bounded by the co-ordinates,
Xl= 9000, Yl =3500
X2 = 10000 4000, Y2 = 3500
X3=9000, Y3= 4500
X4= 10000 -WOO, Y4=4500
(the values taken above are examples for a simple explanation)

(Figure Removed)
APPLICATION OF THE INVENTION
Present invention is well applicable to design a high efficient general illumination optical system, where uniformity, higher coefficient of utilization and no glare on the illuminated area is needed. Especially it is well suited for road illumination.
The above invention of bi-cylindrical lens can be efficiently used in a luminaire for street lighting. The luminaire comprises of a plurality of light modules. Each light module consists of a light source, for example, LED, where each light source is associated with the lens array described in the present invention. The module emits a light beam of particular shape and illumination pattern. The lighting module with its axis aligned at an angle with the axis of luminaire directs emitted light towards center of a predetermined segment which is to be illuminated.
The above invention can also be used in areas where sharp boundaries of the light spot emitted from the lens array are needed, as in the case of theatrical lights. In fields like this, focused light spot is needed to highlight an important spot, and the areas around this important spot are needed to be kept in dark. Hence, the illuminance has to be controlled or restricted to this spot only. Using the lens array described here, this need can be fulfilled.

The present invention has been described by taking the example of segmented illumination, any equivalent variation made to the technical features without departing from the claims of the present invention as defined by the appended claims.

We claim:
1) (New independent claim) A bi- cylindrical lens and a lens array of such bi-cylindrical
lenses, where the bi- cylindrical lens comprises of a front surface and a back surface,
possessing a set of structural parameters, the parameters include a front cylindrical axis
rotation (FAR) with respect to length and width of the bi- cylindrical lens; a back
cylindrical axis rotation (BAR) with respect to length and width of the bi- cylindrical
lens; the said FAR and BAR are rotated such that they are inclined at angles with respect
to length and width of the lens, where the rotation changes the curved surface areas of the
front and back cylindrical surfaces of the bi-cylindrical lens, in order to achieve uniform
illumination and a desired shape and pattern of illumination on a surface with a sharp cut-
off boundary.
(CANCELLED)
2) (Additional claim) The bi- cylindrical lens as described in claim 1. where in shape of each bi- cylindrical lens is convex, concave or combination of concave and convex.
3) The bi- cylindrical lens array in as described in claim 1 , wherein each bi- cylindrical lens has its own set of independent structural parameters depending on required shape and illumination pattern distribution and on the location of the surface.
4) The bi- cylindrical lens lens array as described in claim 1, wherein shape of the bi- cylindrical lens is convex in the lens array.
5) The bi- cylindrical lens lens array as described in claim 1, wherein shape of the bi- cylindrical lens is concave in the lens array.
6) The bi- cylindrical lefts lens array as described in claim 1, wherein shape of the bi- cylindrical lens is a combination of convex and concave in the lens array.
7) The bi cylindrical lens array as described in claim 12, where m each set of parameters for the bi- cylindrical lens are either same or different from each other in the lens array.