WO2001057559A1

WO2001057559A1 - Multiflecting light directing film

Info

Publication number: WO2001057559A1
Application number: PCT/US2000/002625
Authority: WO
Inventors: Richard W. Clikeman; Neil D. Lubart; Charles R. Mayfield
Original assignee: Trivium Technologies, Inc.
Priority date: 2000-02-02
Filing date: 2000-02-02
Publication date: 2001-08-09
Also published as: CN1452722A; CA2399065C; CA2399065A1; BR0017088A; CN100416306C; AU2000226369B2; EP1266247A1; AU2636900A; JP2004519700A; EP1266247A4; HK1060183A1; MXPA02007489A

Abstract

A transflector which simultaneously maximizes light reflectivity from one side of the transflector while maximizing light transmissivity from the opposite side of the transflector. This is achieved by configuring the transflector with distinct regions of transparency and reflectivity. The transflector is composed of a transparent material (31), serving as a body, for transmitting light ray (36) therethrough. The transflector further includes reflective regions (32) composed of a reflective material (33), such as aluminum or silver, for reflecting light ray (35) away from the transflector.

Description

MULTΓFLECTΓNG LIGHT DIRECTING FILM

Background-Field of Invention

This invention relates to all applications where there is a requirement in which reflectivity of incident light (visible through infrared) in one direction and transmissivity in the opposite direction are simultaneously enhanced. That is, the sum of the reflectivity from one side and the transmissivity from the other side exceeds 1.0. Such a film will hereinafter be called a multiflector.

One application area is for solar collection in which transmission of light would be maximized (reflectivity minimized) in the direction facing the sun and reflectivity maximized (transmissivity minimized) in the direction facing the collector. The invention will significantly increase the level of retained energy in such devices. Additionally, the invention could be used as part of a heating, cooling and/or power generating system in which solar energy is utilized for some or all of the power generation. The invention will increase the efficiency of solar collectors and will thus reduce the use of fossil fuels.

A second application area includes use with any non-emissive display technology — such as electrochromic, ferroelectric, ferromagnetic, electromagnetic, and liquid crystal — where it is desired to use both externally generated (ambient) light and internally generated (artificial) light. The film is a replacement for the transflective/reflective/transmissive element of the non- emissive displays, where the replaced element is either independent of or integral to the internally generated light (backlight system). Use of this film will allow brightness contributions simultaneously from artificial light and ambient light such that systems will see a significant decrease in power usage. In system where a battery is used for some or all of the power supply, battery life can be increased by as much as 174%.

A third application area includes building materials in which a film can be used to direct light from a light source (such as a window or skylight) while at the same time reflecting ambient light within a building or structure. Backfire und-Description of Prior Art Solar Collectors

The prior art for solar collectors includes photovoltaics where sunlight is converted directly to electricity, solar thermal energy used to heat water, and large scale solar thermal power plants used to generate electricity. In these systems solar energy is "collected" by placing panels or arrays of panels in the direct path of the sun. These panels are composed of mirrors or mirror-like material to reflect solar energy to a specific point for collection, or are made up of a variety of absorbent materials. Systems where absorbent materials are used can be further be divided into systems where solar energy is collected in cells or where solar energy is absorbed as thermal energy to heat either water or a heat-transfer fluid, such as a water-glycol antifreeze mixture. Most commercially available solar cells are made from wafers of very pure monocrystalline or polycrystalline silicon. Such solar cells, typically, can attain efficiencies of up to 18% in commercial manufacture. The silicon wafers used to make them are relatively expensive, making up 20-40% of the final module cost. The alternative to these "bulk silicon" technologies is to deposit a thin layer of semiconductor onto a supporting material such as glass. Various materials can be used such as cadmium telluride, copper-indium-diselenide and silicon. There are basically three types of thermal collectors: flat-plate, evacuated-tube, and concentrating. A flat-plate collector, the most common type, is an insulated, weatherproofed box containing a dark absorber plate under one or more transparent or translucent covers.

Evacuated-tube collectors are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber, covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ("evacuated") from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss. Concentrating collector applications are usually parabolic troughs that use mirrored surfaces to concentrate the sun's energy on an absorber tube (called a receiver) containing a heat-transfer fluid.

Emissive Displays The prior art for non-emissive displays, particularly liquid crystal displays, include either reflective displays or surface light source (transmissive) displays, commonly denoted backlit displays. The conventional reflective display which uses a reflective film as the bottom layer to redirect ambient light back through the display elements has a composition as illustrated in figure 1. In this drawing ambient light 10 (sunlight, artificial light - such as office lighting - or from a light source attached to the top of the unit 11) enters the display unit, passes through the various layers of the unit, 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension, and is redirected from the reflective film 9 back through the various layers to produce an image. This method of creating an image with available ambient light is limited by the available light. This method is not an effective means for producing high quality graphic images and severely limits the quality of color images in a variety of conditions. The conventional backlit (transmissive) display has a composition as illustrated in figure 2. In this drawing, light is produced with a backlight assembly 7 and directed as light ray 13, through the various layers, such as 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension, to produce an image. This method of producing an image with artificial light is limited by the amount of ambient light and, in systems where a battery is used some or all of the time to generate power, by limited battery life. When ambient light is present, glare is created by light reflecting off the various layers, as described above, without passing through all the layers 6 through 8. To overcome this glare and to produce an image that is palatable to a user, the backlight gain must be increased to produce more usable light, i.e. more light passing through layers 6 through 8. This increase in artificial light causes an added drain on the battery and thus reduces the usability of the system to which the display is attached. As ambient light increases, glare increases and thus, at some point the backlight becomes ineffective in producing a palatable image.

Previous attempts to use simultaneously the ambient light and a backlight have resulted in applications that compromise both the transmissive qualities and the reflective qualities of the display. Hochstrate, in U.S. 4,196,973 teaches the use of a transflector for this purpose. Weber, in U.S. 5,686,979, col. 2, teaches the limitations of the transflector for this purpose and alternatively proposes a switchable window that at one time is wholly transmissive and at another time is wholly reflective. Building Materials

The prior art for building materials is related to films or coatings for light sources (such as windows, skylights, or light pipes) in which the control of transmittance and/or reflection of light is desired. Films or coatings generally fall within two categories: tinting or reflecting materials. Tinting materials have the quality of reflecting a certain percentage of light from one side of the film while transmitting the remainder of the light. In tinting films or coatings, the ratio of transmittance/reflectance is determined by the properties of the material(s), and is the same on either side of the film (Reflectivity R + Transmissivity T =1). For reflective films or coatings, the reflectivity R is less than or equal to 1, where the limit is determined by the properties of the material.

Objects and Advantages

A primary object of this invention is to direct light in such a manner as to reflect incoming light from one direction with minimal loss of said light and with controlled redirection of said light, while at the same time transmitting light from the opposite direction with minimal loss of said light and with minimal redirection of said light.

Another object of this invention is to direct light in such a manner as to transmit incoming light from one direction with minimal loss of said light and with minimal redirection of said light, while at the same time reflect light from the opposite direction with minimal loss of said light and with controlled redirection of said light in such a manner as to contain said light within a system, i.e. solar collector, or structure (such as an office building, museum, etc.).

The Multiflecting Light Directing Film according to the present invention will increase the brightness and reduce the effects of glare in systems where this is required and/or will increase the efficiency of systems where containing light is required.

Brief Description of the Drawings

Figure 1 (prior art) is a diagram showing the operation of a conventional reflective display. Figure 2 (prior art) is a diagram showing the operation of a conventional backlight display.

Figure 3 is a diagram showing the general features of a backlight embodiment of the present invention. Figure 4 is a diagram showing the general features of a solar panel embodiment of the present invention.

Figure 5 is a diagram showing the typical composition of a non-emissive display utilizing the present invention.

Figure 6 is a diagram showing the operation of an embodiment of the present invention utilizing a collimator.

Figure 7 is a diagram showing a cross section of an embodiment of the present invention and the associated light paths.

Reference Numerals in Figures 1-5 6 polarizers

7 glass plates

8 liquid crystal suspension

9 reflective film

10 ambient light from sun or room 10A light ray striking absorber directly

10B light ray strikes absorber directly, is reflected off absorber, is reflected off base of reflective structure back to absorber, etc.

IOC light ray strikes side of reflective structure and is directed to absorber, is reflected off absorber, is reflected by base of reflective structure back to absorber, etc.

11 controllable source of light from exterior of display

12 backlight assembly

13 light ray from backlight assembly

14 transparent material of the multiflector 15 reflective material of the multiflector

16 remainder of the non-emissive display system 17 base of the reflective structure

18 spacing between reflecύve structures at the base

19 thickness of the multiflector film

20 height of the reflecting structure from base to apex 21 the number of reflecting structures per pel (picture element of display)

22 multiflector in cross-section

23 the sun

24 absorbing material in a solar collector

Detailed Description of the Preferred Embodiments

The film material will be transparent and will be designed as an integral element of the system in which it is a part. The film contains a set of indentations, or discrete shapes, which are filled with reflective material(s). The cross section of the indentations may assume the shape of a triangle or other polyhedron which may be arranged in a variety of patterns. The indentations may be replaced by a series of discrete objects such as pyramids, cones, or any polyhedron, and likewise may be arranged in a variety of patterns. The discrete faces of the indentations or objects may be planar, concave, convex, or pitted such that light reflecting from any face may be controlled. The preferred material for filling the indentations is a material with high reflectivity such as aluminum or silver, but may be a composite paste, a composite material, or multiple materials with different refractive indices or reflective qualities. The reflective material is embedded in the transparent material such that the base of each shape is approximately parallel to and coincident with, or slightly recessed from the transparent material. The indentations, or discrete objects, are repeated in parallel and spaced across the area of the film. The indentations, or discrete objects, may be arranged in varying shapes, heights, angles, or spacings before a pattern is repeated.

In Figure 3, let 14 represent the transparent material, 15 represent the reflective indentations or objects, 12 represent the backlight assembly, and 16 represent the remainder of the non-emissive display system and the direction from which the display is viewed. Let: 17 = r = half width of base of the groove, or object

2r = base of groove, or object

/ = multiple of the half width of base of the groove

18 = fr = spacing between indentations

19 = Th = film thickness (based on the height of the groove, or object, and is determined by the nature of the transparent material)

K = multiple of the half- width of base of the groove

20 = Kr = height of groove, or object

21 = M = number of indentations per pel (picture element) defined here as the smallest controllable area of the display

Also let

R_M2 = reflectance of the reflective material to normally incident light 22 represent the invention as a whole

The mirror-like and funnel effects can be accomplished by using a combination of appropriate (1) shaping of the material comprising the film and (2) choice of materials with either different reflectivities, indices of refraction, composites, or a combination of the two. The light directing/Tunneling structures and/or microstructures include, but are not limited to indentations (intersecting or not), cones or other conic sections, multi-sided structures (regular or not) such as pyramids or tetrahedrons, all structures of the same or different sizes generally varied periodically and in which the reflectance, transmittance, and absoφtion of the film might have different values. This enables the achievement of high reflectivity and low transmissivity through the film in one direction and high transmissivity and low reflectivity in the other direction.

R, = reflectivity from one side T, — transmissivity from one side

A, = absorptivity from one side R₂ = reflectivity from the other side T₂ = transmissivity from the other side A₂ = absoφtive from the other side From the conservation of energy: R, + T, + A, = 1 and R₂ + T₂ + A₂ = 1 In the prior art of transflectors, R = R, = R₂; T = T, = T₂; and A = A, = A₂. It follows that in the prior designs, R + T = 1 when A = 0. Even where prior art claims to overcome the limit of transflectors and where the disclosed transflector is meant to channel or direct light, no overall transmitance or reflectance is shown so that any possible gain cannot be determined and is not apparent.

In this art, the value of the reflectance on one side of the film is significantly decoupled from the value of the reflectance on the other side, and the value of the transmissivity on one side is significantly decoupled from the value of the transmissivity on the other side. This newly disclosed film allows R, ≠ R₂, T, ≠ T₂, and A, ≠ A₂. A specific embodiment will be shown below in which T,, R₂, A,, and A₂ are small. It follows that R, + T₂> 1. This disclosed film multiplies the transflecting effect. In the theoretical limit, for this non-emissive version of the film, T, = R₂ = A, = A₂ = 0. Then R, + T₂ = 2.

The first embodiment of the film is related to uses in which light is to be directed without regard to dispersion upon transmission, in particular for use in solar collectors or any device in which radiated light is to be directed or collected as illustrated in Figure 4. In this drawing light from the sum 23 enters the transparent material 14 as light ray 10A and is transmitted directly to an absorbing material 24. Light ray 10B passes through the transparent material 14 and is partially reflected by the absorbing material 24. Light ray IOC passes through the transparent material 14 and is redirected by the reflecting structure 15 to the absorbing material 24, is partially reflected by the absorbing material 24. The film material will be highly optically transmissive to visible, ultraviolet, and/or near infrared light between about 300-2,500 nanometers, stable to ultraviolet light, impervious to moisture, non-hygroscopic, scratch resistant, and easy to keep clean, with an appropriately chosen refractive index to match the other elements of the system in which it is a part. The adhesive is highly optically transmissive to light between about 300-2,500 nanometers and stable to ultraviolet light. In the first embodiment, the design is for maximum sum of transmissivity and reflectivity. Then maximum sunlight will be collected and retained within the specific device in which the film is a part. Therefore, for this embodiment, let R_M2 = 1.00; a perfectly reflecting material. Let/= 0.1 , the practical limit for manufacturability of the indentations. Choose values for r and/large enough to avoid diffraction and interference effects. For example, choose r = 200 / so that the spacing between adjacent indentations at the base is 20//, well above the longest wavelength of visible light. For a solar collector where multiple reflections during transmission are insignificant as long as perfectly reflecting material is used, R, = 2 / (2 + )=0.952 and T₂ = 1.000. Thus, R, + T₂ = 1.952, near the theoretical limit of 2.000. Thus, virtually all light energy entering the system will be trapped. The second embodiment of the film is related to use with a non- emissive display system, such as liquid crystal displays, or other devices in which light is directed for the puφose of creating an image. This embodiment of the film may be inserted between the backlight assembly and the remainder of the display system, may be a component of the backlight assembly, or may be attached to a component of the remainder of the display. The preferred artificial light source in this case would include a means of collimating light such that the majority of light emerges peφendicular to the film. The highly transmissive side of the disclosed film faces the backlight system and the highly reflective side faces the viewer. The film will cover the full area of the display. The indentations or objects may be arranged at any angle to the edge of the display, from parallel to oblique.

Non-emissive display systems using the invention will have a composition illustrated in figure 5. In this drawing ambient light 10 will pass through the various layers 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension and will be redirected by the reflective elements of the invention 22, back through the various layers 6 through 8, while at the same time artificial light rays 13 generated from backlight assembly 12 will pass through the transparent elements of the invention 22 may be attached to adjacent elements such as backlight assembly 12 or be installed as a separate layer in the display system. Let

W_τ = width of the display m = number of indentations per pel (picture element) defined here as the smallest controllable area of the display

F_w = format of display in horizontal direction (number of distinct elements, where each element has a red, green, and blue pel) Then r = W_τ / [ 3 F_w m ( 2 +f) ] for a color liquid crystal display. To illustrate the method of design, let W_τ = 246mm and F_w = 800 represent the typical values for a vintage 1996/97 color liquid crystal display design. Also, let m = 3 to eliminate the necessity of alignment of the film with the pels of the display during the display assembly process. Additionally, m may be increased oi decreased as necessary to eliminate visible non- uniformities in the light distribution, such as banding, which may be created by the film.

For the designs shown for the second embodiment, let/= 0.5. This minimizes the redirection of light, preserving the original direction of the transmitted light. For this value of/, 20% of parallel light from the backlight system will be transmitted without reflection, 40%> will be transmitted with one redirection from the reflecting indentations or objects, and 40%> will be transmitted after two redirections from the reflecting indentations or objects. In this instance r can be calculated using the equation r = W_τ / [ 3 F_w m (2 +/) ] to be 13.7 / with a spacing/r (spacing between indentations) of 6.9/ . The reflectance R, and transmittance T₂ can be computed if R_M2 (normal reflectance of the material) is known. Note two design examples:

1. Let R_M2 = 1, then R, = 2/(2 + ) = 0.8. and T₂ = 1.0, resulting in R, + T₂ = 1.8.

2. Let R_M2 = 0.86, then R, = 2 R_M2 (2 +/) = 0.688. and T₂ = 0.840, resulting in R, + T₂ = 1.528.

Both designs show the significant improvement available from use of the multiflector technology in the place of existing transflector technology.

As used herein, a multiflector is a transflector, being a device capable of transmitting and reflecting light.

An embodiment is shown in Figure 6. Let 31 represent the transparent material (body of the element), 32 represent the reflective/refractive shapes, 33 represent a reflective material (where no fill, gas, vacuum, or a change of indices of refraction are used to create structures), and 34 represents a collimating element attached to the Multiflector element. Light ray 35 strikes the base 33 of a shape 32 and is redirected away from the element (reflected). Light ray

36 enters the element from a transmissive energy source (not shown), passes through the collimator 34 without redirection, passes through the body of the element 31 without striking any shaped structures 32 and exits the reflecting side of the element without redirection. Light ray 37 enters the collimator from a transmissive energy source (not shown) at an incident angle greater than 10 degrees and is redirected by the collimator 34 to less than 10 degrees. Light ray

37 enters the body of the element 31 and passes through without being redirected.

Figure 7 represents a cross section of the Multiflector element, where 41 represents the boundary edge of the element. Structure 43 extends into the element a percentage of the total element thickness. Let the apex (tip) of structure 43 have an angle of 4 degrees. Additionally, let the apex of structure 43 face one light source (not shown) while the base of the structure 43 faces another light source (not shown). Light ray 44 enters the element peφendicular to the plane of the element and passes through the element without striking a shaped structure 43 and exits the element without redirection. Light ray 45 enters the element peφendicular to the plane of the element and strikes the midpoint of a structure 43 and is minimally redirected (4 degrees relative to peφendicular to the plane of the element) such that it exits the element without striking an adjacent structure 43. Light ray 46 enters the element peφendicular to the plane of the element and strikes a structure 43 near the apex (tip) and is minimally redirected (4 degrees relative to peφendicular to the plane of the element) such that it strikes an adjacent structure near the base of the structure (16.6% of the height of the structure) and is again minimally redirected (as above) such that the total redirection of light ray 46 is 8 degrees from the peφendicular to the plane of the element upon exiting the element. Light ray 47 enters the element at an angle greater than 10 degrees of peφendicular to the plane of the element and strikes a structure 43 above the midpoint and is minimally redirected (4 degrees relative to peφendicular to the plane of the element). Due to the increased angle of entry of light ray 47, multiple redirections occur before light ray 47 exits the element. In this example, seven redirections are necessary for light ray 47 to exit the element - the cumulative redirection is 28 degrees. Light ray 48 is reflected by a structure 43 at an angle equal to the angle of incidence. Light ray 49 enters the element at a steep angle relative to the peφendicular to the plane and strikes a structure 43 near the apex (tip), due to the cumulative redirection light ray 49 cannot exit the opposite side of the element.

Figure 7 is configured with structures 43 at an aspect ratio of 14.3, a spacing between structures 43 of 25% of the base width, and structures evenly spaced across the body of the element 42. Such an element will produce a transmissivity of 94% of light rays entering the element peφendicular to the plane from the side closest to the apex (tip) of structures 43 (transmissive side). The element described above will provide the additional benefit of reflecting 76% of light striking the element from the opposite direction. In this example, 20% of light entering from the transmissive side will pass through the element without redirection, 40% will pass through with a single redirection (4 degrees relative to peφendicular to the plane of the element) and 40% of the light will have two redirections (8 degrees relative to peφendicular to the plane of the element). This example provides an R + T of 1.70.

The combination of aspect-ratio and spacing of structures described above are intended to illustrate the effects of configuration of the element and are not intended to be limiting. Another embodiment of the invention is related to uses in which light is to be directed or focused upon transmission, in particular for use in building materials where light from the sun is used to illuminate an interior area or augment artificial lighting. In this embodiment the indentations, or objects, may be angled such that the base of the indentation, or object is not parallel or coincident with the boundary of the transparent material. This embodiment will allow the light to be directed at a given angle to the transparent material independent of the angle of the light source.

The present invention may be stated as being a transflector having means for reflecting of light impingent thereon from a first direction, and having means for transmitting of light arriving from a direction opposing to said first direction wherein the sum of the percent of light being reflected relative to the light coming from the first direction, and the percent of light being transmitted relative to the amount of light coming from the opposing direction, is greater than 100 percent.

The present invention may also be stated as a light transmitting material capable of transmitting light in a first and second direction, having a first surface, said first surface having reflecting means for reflecting a percentage but not all of the light striking said first surface from said first direction, and having one or more reflecting structures associated with said reflector means, said structures having sidewalls extending from said first surface, said sidewalls being at an angle sufficient to reflect light striking said structure from said second direction through said first surface such that a percentage of light from said second direction passes through said first surface, wherein the sum of the percent of light being reflected relative to the light coming from the first direction, and the percent of light being transmitted relative to the amount of light coming from said second direction is greater than 100 percent.

The Multiflector element is independent of any specific system, but will typically be included as one of several elements incoφorated within a system. The Multiflector element will provide optimized reflection of energy in one direction while simultaneously optimizing the transmission of energy in the opposite direction. This is accomplished by utilizing high-aspect ratio structures embedded, embossed, or by other means created in the body of the element. By significantly increasing the surface area of the reflecting/refracting structures in one direction (the apex of the structure) with respect to the base of the structure, the amount of energy that can reflected in one direction can be decoupled from the amount of energy transmitted in the opposite direction.

The Multiflector element can be placed in conjunction with other elements to produce additional effects. In the preferred embodiment, a collimating element may be integrated with the Multiflector to form a single element, attached to the Multiflector, or incoφorated into another component of a system to which the Multiflector is attached, such that the collimating element is proximal to the transmitting side of the Multiflector element and between the element and the transmissive light source. The collimating element accepts incoming energy waves distributed over a broad angle and redirects the energy waves to emerge at an angle less than some specified angle as measured from the normal to the surface of the element. The use of a collimating element ensures that virtually all energy entering the Multiflector element from the transmissive side will be constrained within an arc of about 10° of peφendicular to the plane of the element. Constraining transmitted energy in this manner will improve the performance of the Multiflector element, but is not a requirement for the Multiflector element to produce beneficial effects.

The determining factors for configuring the element are the aspect ratio of the reflecting/refracting shaped structures, spacing between structures, and materials used to construct the element. These factors determine (1) the allowable incident angle of the energy entering the element from one direction (transmissive), (2) the proportion of energy transmitted from that direction, (3) the proportion of energy reflected by the opposite side of the element, (4) the distribution of energy emerging from the element, (5) the percentage of energy lost to internal absoφtion or scattering. Aspect ratio (the ratio of height to base) of the reflecting/refracting shapes determines the relationship between the specific angle at which the transmitted energy enters the element and the angle at which the transmitted energy emerges from the element. The spacing between the shaped structures determines the proportion of energy reflected by the element (from the reflective side) and the distribution of transmitted energy (from the transmissive side). By increasing the spacing between the shaped structures, a smaller proportion of energy is redirected from the transmissive side while reflection of energy from the opposite direction is reduced. Conversely, by decreasing the spacing between the shaped structures, a greater proportion of the transmitted energy will be redirected while a larger proportion of the energy from the opposite direction will be reflected. The general relationship between the aspect ratio of height to base for the reflecting/refracting structures and the spacing between structures is illustrated in the following examples:

Example 1 : A single structure is triangular in cross section and extends along the full length of the element from one side to the other. The above structure is repeated at regular intervals such that one side of the entire body of the element is covered with the bases of alternating triangular rows and spaces in-between. If the specific application requirement for the element calls for approximately 66.6% of the energy from one side (the reflecting side) is to be reflected and the transmitted energy from the opposite side is restricted to emerge about 5°, than the aspect ratio must be a minimum of 11.5: 1. The spacing between the shaped structures in this example will be approximately half the dimension of the base of a shaped structure. In this example the sum of potentially useful reflected energy from one side R plus the sum of potentially useful transmitted energy from the opposite side T is approximately 1.66 (R + T = 1.66). This can be restated as 66.6% of the energy entering the element from the reflective side is reflected and 100% of energy entering the element from the transmissive side is transmitted (R = 66.6% and T = 100% so that R + T - 166%).

Example 2: Assume that the shaped structures are the same as in example 1 and that the specific application requirements call for maximizing the amount of transmitted energy independent of any specific angle of emergence. Also assume that the energy entering the element from the transmissive side is uniformly collimated within about 10^° of peφendicular to the plane of the element.

In this application the requirements are for reflection of about 80% of the energy in one direction (the reflecting side) and for transmission of more than 95% of the energy from the opposite side (the transmitting side). An element with an aspect ratio of 15:1 will be approximately 96.8% transmissive, assuming a perfectly reflecting material for the shaped structures. The spacing between the shaped structures is about one-fourth the dimension of the shaped structures. In this example the sum of potentially useful reflected energy from one side R plus the sum of potentially useful transmitted energy from the opposite side T is approximately 1.77 (R + T = 1.77). Additionally, the element can be configured to specifically control the distribution of both reflected and transmitted energy. As an example, such a configuration may be useful in a display application to improve viewing angle.

A light ray striking a triangular row of structures near the tip will have the most number of redirections before possibly exiting the element. By using basic geometry and a rudimentary understanding of geometric optics, one skilled in the art can calculate what aspect ratio and width between structures is necessary to preferably redirect light striking near the tip no more than twice before exiting. A geometric plot of the light ray path can be used to derive the relationships between the various parameters, including the constraints of the system. The height of the structure will be determined by several factors, among which is the thickness of the transparent material. If the requirement of a specific application is to transmit light through the transflector within 10 degrees of peφendicular, then assuming a height, one can plot or calculate the apex angle. The apex angle and the height will give the aspect ratio and thus the width of the base of the structure. In the preferred embodiment for non-emmisse displays, the element should not exceed

100 mils thickness. The body of the element should have a transmissive co-efficient of > 97%. The apex (tip) of each of the shapes penetrates into the body of the element a percentage of the total thickness between 10% - 100%. Each shape will have a fixed apex angle of between 2.6° - 9.5°, with an altitude to base ratio of between 6:1 - 22:1. In another embodiment, the shape will have a fixed apex angle of between 3.0° - 7.0°, with an altitude to base ratio of between 8:1 - 18: 1. In either embodiment, the altitude to base ratio may be as low as 4: 1. This results in the walls of the structure being at an angle relative to the base of between about 83 degrees to less than 90 degrees. The base of the shape is parallel to a surface of the element and has a base width of between 2.0 - 200.0// (μ = microns). In another embodiment, the base width may be between 2.0/ - 50.0// . Whether the shape is created with fill material or through an optical process, the base of each structure needs to be reflective. This can be achieved either through a fill process, through a deposition/photoresist process, or other methods such as the use of overlays. The triangular row structures are periodically repeated with a fixed spacing between the apex of each triangle of between 3.0 / - 300.0// and the spacing between the base of each adjacent isosceles triangle is between 1.0 / - 100.0//. In another embodiment, the spacing between the apex may be between 3.0/ - 70.0// and the spacing between the bases may be between 1.0/ - 20.0//. In the preferred embodiment, a collimating element is attached to the element adjacent to the transmitting side of the Multiflector element. The dimensions described in the preferred embodiment should not be inteφreted as limitations since other applications may require, or allow, variations on the above specifications In the preferred embodiment, the cross section of a single shape is triangular and extends from one edge of the element to the opposite edge to form a single row and is oriented in the transparent material (body of the element) such that the base of the triangle is parallel to and coincident with, or slightly recessed from, the plane of one surface of the body of the element (the reflective side). In the preferred embodiment, said triangular row is repeated in parallel and evenly spaced across the entire area of the element forming a striped pattern of shapes and spaces. In other embodiments said triangular-shaped rows may be replaced by discrete objects such as pyramids, cones, or any polyhedron, and likewise may be arranged in a variety of patterns to achieve specific effects. In other embodiments, the discrete shapes, as described above, may be arranged in varying shapes, heights, angles, or spacing. In the preferred embodiment, the discrete faces of each triangular row are planar. In other embodiments one or more of the discrete faces of the row, or discrete shapes, may be concave, convex, and/or pitted. Additionally, micro-shapes (such as pyramids or cones) may be deposited on the flattened base of each structure to further control the direction of reflected energy.

In the preferred embodiment, the material for the transparent "body" of the element will have specific properties that minimize absoφtion and redirection of energy - such as internal scattering. In addition, the material for the body of the element will require specific properties necessary for etching, molding, or other processes that alter the body of the element. Examples of suitable materials are polymers such as polycarbonate and PMMA (polymethylmethacrylate). Where etching, molding, or embossing is used to create a series of indentations in the body of the element, fill material such as a highly reflective metal may be used. Additionally, clear material such as a polymer, or no material (gas, air, or vacuum) may be used to fill the indentations. Where clear material or no material is used to fill the indentations, the material chosen for the body of the element should have a higher index of refraction than the fill. The minimum difference in index of refraction between the fill and the body of the element is estimated to be 0.01. In the preferred embodiment, indices of refraction are the same for each shape across the body of the element. For puφoses of the present invention, the term reflection, when discussing light striking the body of the structure, also includes refraction where the difference in the index of refraction of the materials, along with the angle of incidence, results in substantial or near total reflection of the light striking the structure.

Where the indentations are filled with a reflective material, a single material, or composite material, may be used to create the above mentioned triangular rows. The fill material for the reflective shapes will be optimized to minimize absoφtion and have highly reflective properties for the controlled redirection of energy. Examples of suitable materials are aluminum or silver, with a reflectivity of 95% or greater, but may be a composite paste, a composite material, or hybrid materials with different refractive indices or reflective qualities. As described above, the reflective material may be coated on the transparent body, be part of the fill for grooves in the body, or be the base of the refracting structure physically separate from but attached to the transparent body.

A second method of creating the preferred embodiment of the Multiflector element consists of producing the above-described triangular rows in a photosensitive transparent material. The desired shapes are produced by changing the index of refraction in specific areas of the body of the element. In this embodiment, a thin layer of reflective material, such as aluminum, is deposited on one side of the element, adjacent to the base of the triangular rows (reflective side). Regions of the deposition are removed corresponding to the spaces between triangular rows, creating a striped pattern across the element. Utilizing an optical process to change the index of refraction of specific areas of the element will require photosensitive materials that exhibit favorable optical and mechanical properties. In addition to a sufficient photo-induced refractive index change, a suitable set of "writing" wavelengths (typically in the ultraviolet), optical transparency, thin film formability, and mechanical behavior are of great importance. Such materials may be organic polymers that have optimized mechanical behavior, or organic-inorganic hybrids that combine the chemical versatility of organic polymers, i.e. polysilanes, polygermanes, and/or their sol-gel hybrids.

In other embodiments related to utilizing a photosensitive transparent material, discrete shapes may be arranged in varying shapes, heights, angles, or spacing and one or more of the discrete faces of a shape, including the triangular rows, may be concave, convex, and/or pitted. Additionally, micro-shapes (such as pyramids or cones) may be deposited on one side of the body of the element directly over the base of each structure, either as part of a deposition process, described above, or as an independent process, to further control the direction of reflected energy. In other embodiments, the indices of refraction may be different for each discrete shape such that various alternating patterns are produced across the body of the element to achieve specific effects. In other embodiments, a combination of shapes created by filled indentations and altering the refractive index of a photosensitive material may be used to create various patterns across the body of the element.

The term Light, as used in the present invention, encompasses electromagnetic radiation with wavelengths corresponding to visible through infrared. The present invention's apparatus is, however, applicable to any electromagnetic radiation that is capable of being reflected or refracted, subject to the ability to create structures of a size and a material to do so. Specifically, the present invention can find applicability in the radio, radar, microwave, infrared, visible, ultraviolet, x-ray and gamma forms of radiation.

Another method of creating the structures of the present invention is by fabrication of the structures from some suitable material that will maintain integrity in the physical working environment, and suspending the structures by some suitable method. Suspension may be accomplished by the use of wire or some type of filament that forms a grid, but will depend on the specific application and will be apparent to one skilled in the art. This aspect of the invention is useful in solar applications, where the size of transflectors are not limited by the size requirements of non-emissive displays. One of the more common methods of collecting solar radiation is by the use of mirrors to reflect radiation from the sun onto a complex of pipes. The pipe complex consists of a first pipe carrying the liquid to be heated, surrounded by a second pipe. The space between the two pipes will typically be evacuated to decrease the amount of convection and conduction loss. By mounting the present invention's structure within this space between the pipes, the majority of solar radiation from the mirror will be trapped and reflected back onto the pipe to be heated, thus increasing overall efficiency. In most situations, the heated pipe will also be emitting radiation, which will also be trapped and reflected back. Thus solar radiation passes through the transflector, while radiation not initially absorbed by the solar collector, combined with any radiation being emitted from the solar collector due to it's temperature, is reflected back to the solar collector. In this embodiment, the vacuum is the transparent material associated with the structure. In such solar applications, the height of the structure will only be dependent on the spacing between the pipes, and the base of the structure may be large as compared to the use in non-emissive displays. The width of the base may be 3500// or larger, although the smaller size structures will also be applicable to this use. The multitude of structures will preferably be bent around at least a portion of the pipe to improve both the gathering and reflection of radiation. As used in this patent, the term "structure" refers to the shape of the element refracting or reflecting light. The structure may be a physically separate item mounted on or in the light transmittive material, it may be formed or represent a groove or indentation that has been cut into the light transmitting material, or it may be the end result of treatment of portions of the light transmissive material such that a shape having a different index of refraction is formed. Where the transmittive material is a gas or vacuum, as may be found in solar applications, the structure is mounted "in" the material by means of a grid, wire, filament or other such device, with the grid representing a surface of the transflector.

The present invention has the unique ability to reflect and transmit more light than any prior art device. The sum of the percent of light capable of being reflected, plus the sum of light capable of being transmitted, will be greater than 100 percent.

Claims

Having thus described the invention, it is now claimed:

1. A transflector having means for reflecting of light impingent thereon from a first direction, and having means for transmitting of light arriving from a direction opposing to said first direction wherein the sum of the percent of light being reflected relative to the light coming from the first direction, and the percent of light being transmitted relative to the amount of light coming from the opposing direction, is greater than 100 percent.

2. The transflector of claim 1 wherein said transflector has a first surface, wherein said reflecting means comprise a reflective material covering at least a part of said first surface and wherein said means for transmitting light comprises one or more structures associated with said reflective material.

3. The transflector of claim 2 wherein said structure comprise a base and sidewalls, said base associated with said reflective material and wherein said sidewalls are at an angle relative to said first surface sufficient to reflect light striking said structure from said opposing direction through said first surface.

4. The transflector of claim 3 wherein said angle of said sidewall is between 83 degrees and less than 90 degrees.

5. The transflector of claim 4 wherein the base of said structure is a elongated rectangle, said rectangle running in one direction across said first surface.

6. The transflector of claim 5 wherein said rectangle of said base has a length and a width, said width being smaller than said length, and wherein said structure has a height, and the ratio of said height to said width of said base is between about 6 and 22.

7. The transflector of claim 1 wherein said transflector comprises a light transmitting material having a first surface, said first surface having one or more indentations.

8. The transflector of claim 7 wherein said indentations have sidewalls communicating with said first surface and wherein said sidewalls are at an angle relative to said first surface of between about 83 degrees and less than 90 degrees.

9. The transflector of claim 7 wherein the indentation is filled with a reflective material.

10. The transflector of claim 9 wherein the reflective material is selected from the group consisting of aluminum, silver, gold or combinations thereof.

11. The transflector of claim 8 wherein said indentation forms one or more grooves in said light transmitting material, said grooves running in one direction across said first surface.

12. A light transmitting material capable of transmitting light in a first direction, having a first surface, said first surface having reflecting means for reflecting a percentage but not all of the light striking said first surface from an opposing direction, and having one or more reflecting structures associated with said reflector means, said structures having sidewalls extending from said first surface toward said first direction, said sidewalls having an internal angle relative to said first surface of less than 90 degrees, said angle sufficient to reflect light striking said sidewalls from said first direction through said first surface such that a percentage of light from said first direction passes through said first surface, wherein the sum of the percentage of light being reflected relative to the light coming from said opposing direction, and the percentage of light being transmitted relative to the amount of light coming from said first direction is greater than 100 percent.

13. The light transmitting material of claim 32 wherein said reflecting structures are formed in the light transmitting material by treating said material in a manner sufficient to create a different index of refraction from said light transmitting material.

14. An electromagnetic radiation transmitting material capable of transmitting radiation in a first direction, having a first surface, said first surface having reflecting means for reflecting a percentage but not all of said radiation striking said first surface from an opposing direction, and having one or more reflecting structures associated with said reflector means, said structures having sidewalls extending from said first surface toward said first direction, said sidewalls having an internal angle relative to said first surface of less than 90 degrees, said angle sufficient to reflect said radiation striking said sidewalls from said first direction through said first surface such that a percentage of radiation from said first direction passes through said first surface, wherein the sum of the percentage of said radiation being reflected relative to said radiation coming from said opposing direction, and the percentage of said radiation being transmitted relative to the amount of said radiation coming from said first direction is greater than 100 percent.

15. A solar collection device, said device containing a grid and a solar collector, wherein solar radiation passes in a first direction through said grid to said solar collector, and a portion of said solar radiation is reflected from said collector to said grid in an opposing direction, said grid having a first surface, said first surface having reflecting means for reflecting a percentage but not all of the solar radiation striking said first surface from said opposing direction, and having one or more reflecting structures associated with said reflector means, said structures having sidewalls extending from said first surface toward said first direction, said sidewalls having an internal angle relative to said first surface of less than 90 degrees said angle sufficient to reflect said solar radiation striking said structure from said first direction through said first surface such that a percentage of said solar radiation from said first direction passes through said first surface, wherein the sum of the percentage of said solar radiation being reflected relative to the said solar radiation coming from the opposing direction, and the percentage of said solar radiation being transmitted relative to the amount of said solar radiation coming from said first direction is greater than 100 percent.

16. The solar collection device of claim 38 wherein said solar collector generates additional radiation, said additional radiation striking said first surface from said opposing direction, wherein a portion of said additional radiation is reflected back to said solar collector.