USOO8290318B2
`
`(12) United States Patent
`Vasylyev
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,290,318 B2
`Oct. 16, 2012
`
`(54) LIGHT TRAPPING OPTICAL COVER
`
`(56)
`
`References Cited
`
`(75) Inventor: Sergiy Victorovich Vasylyev, Elk Grove,
`CA (US)
`
`(73) Assignee: SVV Technology Innovations, Inc.,
`Sacramento, CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 13/345.738
`
`(22) Filed:
`
`Jan. 8, 2012
`
`(65)
`
`Prior Publication Data
`US 2012/O135512 A1
`May 31, 2012
`
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 12/764.867,
`filed on Apr. 21, 2010.
`(60) Provisional application No. 61/461.522, filed on Jan.
`18, 2011, provisional application No. 61/214.331,
`filed on Apr. 21, 2009.
`
`(51) Int. Cl.
`(2006.01)
`GO2B 6/32
`(2006.01)
`GO2F L/333
`(2006.01)
`HO2N 6/00
`(52) U.S. Cl. ................ 385/33; 385/34; 385/35; 385/36;
`385/900; 349/56; 349/57; 349/58; 349/59;
`349/60; 349/61; 349/62: 349/63: 349/64;
`349/65; 349/66:349/67: 136/246; 136/256;
`136/257
`(58) Field of Classification Search .............. 385/33–36,
`385/900; 349/56-67: 136/246, 256 257
`See application file for complete search history.
`
`
`
`U.S. PATENT DOCUMENTS
`4,461.278 A * 7/1984 Mori ............................. 126,700
`5,801,795 A * 9/1998 Ogino ............................... 349.5
`6,064,452 A * 5/2000 Ogino ............................. 349/57
`6,274,860 B1
`8/2001 Rosenberg
`6,333,458 B1
`12/2001 Forrest et al.
`6,440,769 B2
`8/2002 Peumans et al.
`7,672,549 B2
`3/2010 Ghosh et al.
`7.817,885 B1 * 10/2010 Moore et al. .................... 385/33
`7,873.257 B2 *
`1/2011 Morgan ........................ 385.146
`2004/O103938 A1
`6/2004 Rider
`2008/0223438 A1* 9/2008 Xiang et al. .................. 136,257
`2008/0264483 A1 10, 2008 Keshner et al.
`2008/0271776 A1* 1 1/2008 Morgan ........................ 136,246
`2009/O126792 A1
`5/2009 Gruhlke et al.
`2009/0296194 A1* 12/2009 Gally et al. ................... 359,291
`2010, 0186798 A1
`7/2010 Tourmen et al.
`1 1/2010 Vasylyev
`2010/02784.80 A1
`2011/0226332 A1
`9, 2011 Ford et al.
`1/2012 Vasylyev
`2012fOO12741 A1
`* cited by examiner
`Primary Examiner — Brian M. Healy
`Assistant Examiner — Guy Anderson
`(57)
`ABSTRACT
`A light trapping optical cover employing an optically trans
`parent layer with a plurality of light deflecting elements. The
`transparent layer is configured for an unimpeded light pas
`sage through its body and has a broad light input surface and
`an opposing broad light output Surface. The light deflecting
`elements deflect light incident into the transparent layer at a
`Sufficiently high bend angle with respect to a Surface normal
`and direct the deflected light toward a light harvesting device
`adjacent to the light output surface. The deflected light is
`retained by means of at leastTIR in the system formed by the
`optical cover and the light harvesting device which allows for
`longer light propagation paths through the photoabsorptive
`layer of the device and for an improved light absorption. The
`optical cover may further employ a focusing array of light
`collectors being pairwise associated with the respective light
`deflecting elements.
`15 Claims, 11 Drawing Sheets
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`1.
`LIGHT TRAPPING OPTICAL COVER
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`US 8,290,318 B2
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`2
`harvesting devices and that can provide efficient light trap
`ping with minimal energy loss.
`The present invention solves the above problems by pro
`viding a transparent optical cover structure having one or
`more micro-structured surfaces that allow for trapping the
`incident light within the light harvesting device by means of
`at least TIR and cause the multiple passage of the trapped
`light through the active layer thus improving the light absorb
`tion and device efficiency at the minimum consumption of
`active layer's material. Other objects and advantages of this
`invention will be apparent to those skilled in the art from the
`following disclosure.
`
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention solves a number of light harvesting
`problems within a compact system utilizing efficient light
`deflection and trapping mechanisms. An optically transparent
`layer is provided which can be placed on top of a light har
`vesting device and enhance the useful light absorption in the
`device. The transparent layer employs light deflecting ele
`ments that communicate incident light a sufficiently high
`bend angle within the layer allowing for TIR at its light input
`Surface and increasing the optical path length of light rays
`through the photoabsorptive layer of the light harvesting
`device.
`In at least one embodiment, the present invention describes
`an optical cover which deflects light at a greater propagation
`angle with respect to a surface normal and traps said light by
`means of a total internal reflection which allows for increas
`ing the light path length and for multiple passage of light
`through the photoabsorptive layer of a light harvesting
`device.
`The optical cover includes a layer of optically transparent
`material having a broad light input Surface and an opposing
`broad light output Surface extending generally parallel to the
`light input Surface. The transparent layer is configured for an
`unimpeded transversal light passage in the direction from the
`light input surface towards the light output Surface. The trans
`parent layer includes a plurality of light deflecting elements
`distributed along the prevailing plane of the layer and having
`a cumulative aperture Substantially smaller than the area of
`each of the broad Surfaces. The light input Surface is charac
`terized by a stepped drop in refractive index outwardly from
`the transparent layer and by a critical angle of TIR. Each of
`the light deflecting elements is configured to receive light
`propagating between the input and output Surfaces and bend
`the light to a greater propagation angle with respect to a
`normal to the light input Surface. The propagation angle of the
`deflected light with respect to the surface normal is advanta
`geously selected to be greater than the TIR angle character
`izing the light input Surface.
`The optical cover operates in response to light received on
`the light input surface of the optically transparent layer. At
`least a substantial portion of light received by the apertures of
`light deflecting elements is deflected from the original propa
`gation path at a greater propagation angle allowing for TIR
`from the light input Surface. As light enters a light harvesting
`device adjacent to the light output Surface, an unabsorbed
`portion of light reflecting from the front surface or any of the
`internal layers or Surfaces of the light harvesting device is
`reflected by the light input surface by means of TIR. This
`effectuates recycling of light that cannot be absorbed in a
`single pass through the photoabsorptive layer of the light
`harvesting device.
`In at least one implementation, the light deflecting ele
`ments comprise Surface relief elements. In at least one imple
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of application
`Ser. No. 12/764,867 filed Apr. 21, 2010. This application also
`claims priority from U.S. provisional application serial num
`ber 61/461.522 filed on Jan. 18, 2011 and U.S. provisional
`application serial number 61/214.331 filed on Apr. 21, 2009,
`incorporated herein by reference in its entirety.
`
`10
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH ORDEVELOPMENT
`
`Not Applicable
`
`INCORPORATION-BY-REFERENCE OF
`MATERIAL SUBMITTED ON A COMPACT DISC
`
`Not Applicable
`
`NOTICE OF MATERIAL SUBJECT TO
`COPYRIGHT PROTECTION
`
`A portion of the material in this patent document is subject
`to copyright protection under the copyright laws of the United
`States and of other countries. The owner of the copyright
`rights has no objection to the facsimile reproduction by any
`one of the patent document or the patent disclosure, as it
`appears in the United States Patent and Trademark Office
`publicly available file or records, but otherwise reserves all
`copyright rights whatsoever. The copyright owner does not
`hereby waive any of its rights to have this patent document
`maintained in secrecy, including without limitation its rights
`pursuant to 37 C.F.R.S 1.14.
`
`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
`The present invention relates to a device and method for
`enhancing the light trapping in light harvesting devices. Par
`ticularly, the present invention relates to collecting light from
`a large Surface area of the light harvesting device comprising
`a light absorbing material and trapping the light within the
`device so as to increase the optical path through the light
`absorbing material and improve the useful light absorption.
`More particularly, the present invention relates to enhancing
`the light trapping in photovoltaic Solar panels, light detectors,
`day lighting systems, bioreactors, water light-treatment reac
`tors, and the like.
`2. Description of Background Art
`Many light harvesting devices employ a light-absorbing
`active layer that has at least apartial transparency with respect
`to the incident light or absorbs more weakly in certain wave
`lengths than in the others. Conventionally, the absorption in
`Such devices can be improved by increasing the thickness of
`the active layer. However, this results in the increased system
`dimensions, material consumption, weight and cost. Alterna
`tively, light trapping approaches are well known in which the
`light path is altered within the device by micro-texturing one
`or more device surfaces. While this allows to somewhat
`increase the light path and thus improve absorption compared
`to a non-textured device, a significant portion of the light still
`escapes from the device without being fully absorbed. It is
`therefore an object of this invention to provide an improved
`optical structure that can be used in conjunction with light
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`mentation, the light deflecting elements comprise micro
`scopic Surface cavities. In at least one implementation, Such
`cavities may have a V-shape in a cross-section.
`In alternative implementations, the light deflecting ele
`ments comprise Surface relief features that can be configured
`in different ways. Particularly, the surface relief features can
`selected from the group of elements consisting of prismatic
`grooves, blind holes, through holes, undercuts, notches, Sur
`face discontinuities, discontinuities in said layer, Surface tex
`ture, and Surface corrugations.
`In at least one implementation, each of the light deflecting
`elements comprises a surface inclined atanangle with respect
`to the light input Surface and configured to deflect light by
`means of refraction or a total internal reflection. In at least one
`implementation, the inclined Surface has a planar shape or
`profile. In at least one implementation, the inclined Surface
`has a curved shape or profile.
`In at least one implementation, the optical cover compris
`ing a plurality of light collectors distributed along the prevail
`ing plane of the transparent layer. The light collectors are
`preferably distributed according to the same pattern as the
`plurality of light deflecting elements and pairwise form indi
`vidual opticules with the respective light deflecting elements.
`Each light deflecting element is disposed on the optical axis of
`the respective light collector and in the immediate proximity
`to the focal area of the collector within each individual opti
`cule. In at least one implementation, the optical cover com
`prises a lens array including a plurality of Surface relief fea
`tures disposed in the focal plane of the array.
`In at least one implementation, the optical cover compris
`ing a lens array where each lens of the array has a shape in a
`longitudinal section selected from the group of elements con
`sisting of elongated, cylindrical, square, rectangular and hex
`agonal.
`In at least one implementation, the optical cover comprises
`one or more optical cladding layers.
`In at least one implementation, the optical cover further
`comprises one or more light harvesting devices disposed
`along the light output surface. In at least one implementation,
`the light harvesting device is selected from the group of
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`elements consisting of one or more photovoltaic cells, radia
`tion detectors, light absorbers, photo-chemical reactors and
`photo-bioreactors.
`In at least one implementation, the optical cover has a form
`of a flexible sheet or film and can be bent to any suitable
`shape.
`The present invention provides a number of beneficial ele
`ments which can be implemented either separately or in any
`desired combination without departing from the present
`teachings.
`An element of the invention is an apparatus for collecting
`light over a given area and traveling in a generally transversal
`direction with respect to the light collection area.
`Another element of the invention is the inclusion of an
`optically transparent layer having opposing light input and
`output surfaces and configured for an unimpeded light pas
`sage through its body at least in a transversal direction with
`respect to the either surface.
`Another element of the invention is the inclusion of dis
`tributed light deflecting elements within the interior of the
`transparent layer which increase the propagation angle with
`respect to a Surface normal without reversing the prevailing
`direction of light propagation through the transparent layer.
`Another element of the invention is the use of light deflect
`ing elements comprising a face containing both a reflective
`and transmissive Surface for redirecting the light in relation to
`a normal to the prevailing plane of the transparent layer.
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`4
`Another element of the invention is the use of deflecting
`elements formed in either light input or light output surface of
`the optically transparent layer.
`Another element of the invention is the use of an array of
`light focusing elements which collect and focus the incident
`light onto the respective deflecting elements.
`Another element of the invention is the use of an array of
`deflecting and/or focusing elements which span the Surface of
`the device, or a portion thereof.
`Another element of the invention is the arrangement of the
`respective pairs of the light focusing elements and the light
`deflecting elements into individual opticules which can oper
`ate independently from the other opticules.
`Another element of the invention is an optical cover con
`figured with an attached optically responsive device (e.g.,
`photovoltaic cell or photo reactor).
`Further elements of the invention will be brought out in the
`following portions of the specification, wherein the detailed
`description is for the purpose of fully disclosing preferred
`embodiments of the invention without placing limitations
`thereon.
`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING(S)
`
`The invention will be more fully understood by reference
`to the following drawings which are for illustrative purposes
`only:
`FIG. 1 is a cross-sectional view of an optical cover accord
`ing to at least one embodiment of the present invention;
`FIG. 2 is a schematic perspective view of an optical cover
`portion showing a light deflecting element shaped as an elon
`gated V-groove, according to at least one embodiment of the
`present invention;
`FIG.3 shows another example of a light deflecting element
`comprising a prismatic cavity, according to at least one
`embodiment of the present invention;
`FIG. 4 shows a further example of a surface relief feature
`comprising a pyramidal cavity, according to at least one
`embodiment of the present invention;
`FIG. 5 shows a yet further example of a surface relief
`feature comprising a conical cavity, according to at least one
`embodiment of the present invention;
`FIG. 6 is a schematic perspective view of an optical cover
`comprising a plurality of V-shape prismatic grooves in a
`cylindrical configuration, according to at least one embodi
`ment of the present invention;
`FIG. 7 is a schematic perspective view of an optical cover
`comprising a plurality of V-shape grooves in an axisymmetri
`cal configuration, according to at least one embodiment of the
`present invention;
`FIG. 8 is a schematic perspective view of an optical cover
`comprising a plurality of discrete light deflecting elements
`formed by Surface cavities, according to at least one embodi
`ment of the present invention;
`FIG. 9 is a further example of light deflecting elements
`employing another-shape cavities, according to at least one
`embodiment of the present invention;
`FIG. 10 is a schematic perspective view of an optical cover
`comprising cavities or V-grooves and further employing a
`lens array, according to at least one embodiment of the
`present invention;
`FIG. 11 is a schematic perspective view of an optical cover
`with a different disposition of cavities or V-grooves with
`respect to a lens array, according to at least one embodiment
`of the present invention;
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`FIG. 12 is a schematic perspective view of a rectangular
`lens array employing cylindrical (linear-focus) lenses;
`FIG. 13 is a schematic perspective view of a rectangular
`lens array employing square-shaped point-focus lenses, in
`accordance with at least one embodiment of the present
`invention;
`FIG. 14 is a schematic perspective view of a rectangular
`lens array employing hexagon-shaped point-focus lenses, in
`accordance with at least one embodiment of the present
`invention;
`FIG. 15 is a schematic perspective view of an optical cover
`illustrating an exemplary lenticular configuration employing
`a planar transparent layer and a lens array, according to at
`least one embodiment of the present invention;
`FIG. 16 is a schematic cross-sectional view of an optical
`cover illustrating its operation in conjunction with a light
`harvesting device, according to at least one embodiment of
`the present invention;
`FIG. 17 is a schematic view, in a cross-section, and ray
`tracing of a light harvesting system employing an optical
`cover in accordance with at least one embodiment of the
`present invention;
`FIG. 18 is a schematic view, in a cross-section, and ray
`tracing of a light harvesting system employing an optical
`cover in an alternative exemplary configuration, according to
`at least one embodiment of the present invention;
`FIG. 19 is a schematic view, in a cross-section, and ray
`tracing of a Sunlight harvesting system employing an optical
`cover and photovoltaic devices inaccordance with at least one
`embodiment of the present invention;
`FIG. 20 is another example and raytracing of a sunlight
`harvesting system employing an optical cover and photovol
`taic devices in accordance with at least one embodiment of
`the present invention;
`FIG. 21 is a further example and raytracing of a Sunlight
`harvesting system employing an optical cover and liquid
`carrying photo reactor, in accordance with at least one
`embodiment of the present invention;
`FIG. 22 is a schematic view, in a cross-section, and ray
`tracing of a an optical cover showing microstructures associ
`ated with a lens array, according to at least one embodiment of
`the present invention;
`FIG. 23 is a schematic cross-sectional view showing an
`exemplary individual light deflecting element and raytracing,
`according to at least one embodiment of the present inven
`tion;
`FIG. 24 is a schematic view, in a cross-section, illustrating
`a step in making an optical cover, according to at least one
`embodiment of the present invention;
`FIG. 25 is a schematic view of an optical cover in a sheet
`roll form, according to at least one embodiment of the present
`invention;
`FIG. 26A through FIG. 26F illustrate various cross-sec
`tions of light deflecting elements.
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`A wide range of applications exist for the present invention
`in relation to the collection of electromagnetic radiant energy,
`Such as light, in a broad spectrum or any Suitable spectral
`bands or domains. Therefore, for the sake of simplicity of
`expression, without limiting generality of this invention, the
`term “light will be used herein although the general terms
`'electromagnetic energy', 'electromagnetic radiation'.
`“radiant energy' or exemplary terms like “visible light'.
`“infrared light', or “ultraviolet light” would also be appropri
`ate.
`FIG. 1 illustrates the present invention and shows a cross
`sectional view of an embodiment of a light trapping optical
`cover 2. Optical cover 2 comprises a layer 8 of essentially
`transparent refractive material confined between broad sur
`face 10 and an opposing broad surface 12. Both surfaces 11
`and 12 are broadly extending both longitudinally and laterally
`so that the thickness of transparent layer 8 is substantially
`Smaller compared to its other two dimensions.
`Both surfaces 10 and 12 are also essentially smooth and
`transparent and are configured for a good optical transmission
`in either direction. Layer 8 is configured for a generally
`unimpeded light passage through its body in either direction.
`Particularly, layer 8 should allow for an unimpeded light
`passage of light through any parts of the layer in the transver
`sal direction. Layer 8 should also be sufficiently transparent
`and allow light to travel considerable distances within the
`layer along the layer's prevailing plane.
`Optical cover 2 is generally designed to be laid flat on top
`of a light harvesting device (not shown in FIG.1) where either
`one of surfaces 10 and 12 can be designated to be a light input
`Surface facing the light source while the other surface can be
`designated to be a light output surface facing the light har
`vesting device. In operation, cover 2 and the underlying light
`harvesting device may be positioned with their prevailing
`Surface planes perpendicular to the light source direction.
`However, they may also be designed to operate at any angle
`other than normal.
`The refractive material of layer 8 should be high enough so
`that when optical cover 2 is coupled to a light harvesting
`device, the light input surface of layer 8 can form an optical
`interface characterized by a stepped drop in refractive index
`outwardly from said layer. It will be appreciated by those
`skilled in the art of optics that when referring to light or other
`waves passing through a boundary formed between two dif
`ferent refractive media, Such as air and glass, the ratio of the
`sines of the angles of incidence and of refraction is a constant
`that depends on the ratio of refractive indices of the media.
`Referring to the refractive medium of layer 8 and the outside
`medium immediately adjacent to the light input Surface, it
`will be appreciated that the following relationship can
`describe light bending properties of the optical interface
`formed by the light input Surface: n sincp in sin (p, where n
`and n are the refractive indices of the material of layer 8 and
`the outside medium, respectively, and (p and (p are the
`respective propagation angles that light makes in respect to
`the surface normal. It will be further appreciated that, in
`respect to the light internally striking the light input Surface
`from layer 8, the same optical interface can also be charac
`terized by the angle of a Total Internal Reflection (TIR) which
`is the value of p for which p equals 90°. ATIRangle (p
`can
`be found from the following expression:
`(parcsin (n/nsin 90') arcsin (n/n). In an exemplary
`case of the interface between glass with the reflective index in
`of about 1.51 and air with n of about 1. p
`is approximately
`equal to 41.47°.
`Layer 8 comprises a plurality of light deflecting elements
`14 within the boundaries formed by surfaces 10 and 12. Light
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`DETAILED DESCRIPTION OF THE INVENTION
`
`Referring more specifically to the drawings, for illustrative
`purposes the present invention is embodied in the apparatus
`generally shown in the preceding figures. It will be appreci
`ated that the apparatus may vary as to configuration and as to
`details of the parts without departing from the basic concepts
`as disclosed herein. Furthermore, elements represented in one
`embodiment as taught herein are applicable without limita
`tion to other embodiments taught herein, and in combination
`with those embodiments and what is known in the art.
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`US 8,290,318 B2
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`deflecting elements 14 are spaced apart from each other and
`distributed along the prevailing plane of cover 2. Each light
`deflecting element 14 has a Substantially smaller aperture
`than the light receiving aperture of optical cover 2. Further
`more, the aperture of each light deflecting element 14 is
`preferably Smaller than the adjacent spacing area so that the
`plurality of light deflecting elements 14 cumulatively occu
`pies a sufficiently small area compared to either surfaces 10
`and 12.
`According to an aspect of the present invention, it is pre
`ferred that each light deflecting element 14 is configured to
`communicate a generally greater bend angle to light propa
`gating between Surfaces 10 and 12 compared to the case when
`light passes through layer 8 simply by crossing Surfaces 10
`and 12 and without striking any light deflecting element 14.
`Each light deflecting element 14 should preferably be config
`ured to alter the ordinary light path between surface 10 and 12
`yet providing for an unimpeded passage of incident light
`through layer 8.
`By way of example and not limitation, light deflecting
`elements 14 may be configured to receive light incident onto
`the light input Surface of layer 8 at normal angles (which
`corresponds to Zero incidence angles with respect to a Surface
`normal) and deflect it at an angle greater than TIR angle (p.
`with respect to the Surface normal. In a further non-limiting
`example, each light deflecting element 14 may be configured
`to receive a fan of rays having a predefined angular spread and
`deflect each ray from the original propagation path so that at
`least a Substantial part of deflected light rays continues propa
`gating through layer 8 but at generally greater propagation
`angles with respect to a normal to the prevailing plane of the
`layer. Similarly, it may be preferred that the new propagation
`angles, after deflection, are greater than TIR angle (p
`at the
`optical interface formed by the light input surface of layer 8.
`Accordingly, when Surface 10 is designated as the light input
`surface, at least a substantial portion of light deflected by each
`element 14 should be communicated a propagation angle
`greater than the TIR angle at the boundary formed by surface
`10. When surface 12 is the light input surface, the propagation
`angle of the deflected light should be generally greater than
`the TIR angle at the boundary formed by that surface.
`Let’s define a propagation angle (p, being the angle that a
`light ray makes with respect to a normal to the prevailing
`plane of layer 8 and, consequently, of optical cover 2. Let's
`further define angle (p, as being counted off from a reference
`direction along said normal which indicates the prevailing
`direction of light propagation through optical cover 2. For
`example, when surface 10 of is the light input surface and
`surface 12 is the light output surface of layer 8, the prevailing
`propagation direction will be the direction from surface 10 to
`Surface 12 along the Surface normal. Likewise, when Surface
`12 is receiving light and Surface 10 is the opposing light
`output surface, the prevailing direction of light propagation
`through cover 2 will be the direction from surface 12 to
`surface 10 along a surface normal. It will be appreciated that,
`when surfaces 10 and 12 are parallel to each other, a normal to
`one of the surfaces will also be a normal to the other surface
`and to the prevailing plane of layer 8 and cover 2. It will
`further be appreciated that, in accordance with the above
`definitions, propagation angle (p, may take values from 0 to
`1800.
`According to a preferred embodiment of the present inven
`tion, light deflecting elements 14 are designed to result in the
`propagation angle (p, being greater than TIR angle (p
`at the
`optical interface formed by the light input surface of layer 8
`and less than 90°. This ensures that the light deflection by
`elements 14 will not prevent light from reaching the light
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`Case 6:20-cv-00139-ADA Document 1-2 Filed 02/21/20 Page 16 of 23
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`output surface yet providing for a Substantial light deviation
`from the original propagation path and enabling TIR at the
`light input surface of layer 8. By using the above notations for
`the refractive indices, a preferred propagation angle (p, of
`light deflected by light deflecting elements 14 may thus be
`expressed by the following relationship: arcsin(n/
`n)<p,<90°.
`In FIG. 1, light deflecting elements 14 are exemplified by
`high aspect ratio prismatic cavities formed in broad Surface
`10. Each of the high aspect ratio prismatic cavities may be
`characterized by two generally planar and symmetrically dis
`posed faces located between surfaces 10 and 12 and inclined
`at an angle with respect to both Surfaces. In at least some
`embodiments of the present invention and in the context of
`describing a Surface microstructure element, such as, for
`example, a Surface cavity having a prismatic or conical shape,
`the term “high aspect ratio” is meant to mean a geometric
`configuration of the microstructure element, in a cross-sec
`tion, where the height or depth of the microstructure element
`is approximately equal or greater than its base at the Surface.
`This term also includes the case when the height of the micro
`structure element is much greater than the base thus corre
`sponding to a deep drawn cavity or a hole with almost vertical
`walls.
`According to an embodiment of the present invention illus
`trated in FIG.1, an individual light deflecting elements 14 can
`be viewed as any suitable localized interruption or alteration
`of the otherwise smooth surface 10 that alters the optical
`interface properties of the Surface in Such a way that a fan of
`rays entering layer 8 through any element 14 will have a
`diff