WO2002055927A2

WO2002055927A2 - Surface with angularly dependent light transmission

Info

Publication number: WO2002055927A2
Application number: PCT/IL2002/000019
Authority: WO
Inventors: Rami Kalfon
Original assignee: Pasit Ltd; Rami Kalfon
Priority date: 2001-01-09
Filing date: 2002-01-08
Publication date: 2002-07-18
Also published as: IL140816A0; AU2002219491A1; WO2002055927A3

Abstract

A window (46) with angularly dependent light transmission, provided by means of a transmissive panel (80, 82, 100, 102, 110, 112) with an array of rows of prismatic shape (48, 86) aligned at an angle to a window edge, such that the desired transmission characteristics are optimized as a function of the sun's path across the sky, thereby increasing the efficiency of the angularly dependent transmission of the window. The window can be equipped with two such panels, and the overall transmission characteristics can be tuned by optical design optimization methods to minimize the changes in transmission through the window during the course of the day, or to generally optimize desired transmission characteristics during the course of the day or as a function of seasonal changes in incident solar radiation. Furthermore, the optimization process can be utilized to reduce viewing distortion through the window.

Description

SURFACE WITH ANGULARLY DEPENDENT
LIGHT TRANSMISSION
FIELD OF THE INVENTION
The present invention relates to the field of surfaces which allow variable light transmission through them as a function of the angle of incidence of the light thereon, especially for use in controlling the amount of solar radiation transmitted.

BACKGROUND OF THE INVENTION
A number of methods have been described in the prior art for varying the percentage of transmission of light through a transparent surface, as a function of the angle of incidence of the light on the surface. Such methods are used on windows in order to regulate the entry of the sun's rays into the interior of a windowed volume. They allow the entry of direct rays when the sun is low in the sky, and therefore not too hot, and stop the transmission of the sun's rays when the sun is high in the sky and hot.

In U. S. Patent No. 4,519,675, to Bar-Yonah for Selectively Light
Transmitting Panel, and in a number of prior Patents cited therein, especially
German Published Patent Application No. 1,171,370 to A. Grün, there are described methods of using the internal reflection properties of light within 90 triangular prisms in order to regulate the transmission of light through a surface made of an array of such prisms. However, although such surfaces should be environmentally advantageous in saving heating costs in winter and cooling costs in summer, and at low capital expenditure, they suffer from a number of drawbacks and disadvantages which have limited their usefulness, and they have not achieved widespread deployment.

Amongst these disadvantages are: (i) The difficulty of designing the optimum panel for the particular application desired, whether in terms of the location, direction or inclination of the window to be made selectively transmissive.

(ii) The direction of the prismatic structure is only disclosed aligned parallel with a side of the window, with the result that when the direction of incidence of the light on the window is not perpendicular to that side of the window, there is comparatively low overall efficiency of the modification of the transmissive properties of the surface as a function of incident angle. Furthermore, this prior art structure limits the ability to achieve a specific transmission objective.

(iii) The level of distortion of the light transmitted through the window to an observer, as measured in any viewing direction.

(iv) Distortion or scattering arising from a lack of geometric perfection of the prismatic shapes in the surface, and the inability to prepare prismatic surfaces without these geometric imperfections.

(v) Limitations engendered by the use of triangular prisms only.

(vi) Limitations engendered by the use of triangular prisms having a 90 angle only.

There therefore exists a serious need for a surface with angularly dependent light transmission which overcomes the disadvantages of such prior art surfaces, and which can be easily manufactured and installed at low cost, in order to enable more widespread use of such surfaces.

The disclosures of all publications mentioned in this section and in the other sections of the specification, are hereby incorporated by reference, each in its entirety.

SUMMARY OF THE INVENTION
The present invention seeks to provide a novel window construction made up of one or more transparent surfaces, each of which preferably has a repetitive array of rows of a geometric form, such as a prismatic form of a triangular or a more complex cross-section, such as trapezoidal or pyramidal shape. The shapes are such that, due to internal reflections, only a fraction of the light incident on them is transmitted therethrough, and that fraction of light transmitted is a function of the angle of the incident light. The term surface is used in this application to describe either the structure present on a sheet or layer of transmissive material operative to amend its optical transmission properties, or the structured sheet or layer itself.

The transmissive surface of the present invention differs from prior art surfaces in a number of ways.

According to a first preferred embodiment of the present invention, the direction of the rows of geometric form, of whatever shape or angle, are aligned at an arbitrary inclination relative to a window edge. In both the above-mentioned
U. S. Patent No. 4,519,675, and in German Published Patent Application No.

1,171,370, there are described only windows wherein rows of right angled prisms are aligned parallel to a window edge and the direction of incidence of the incident radiation is always shown coming at right angles to the direction of the rows of prisms. As a result, the transmission characteristics are limited, since, when the direction of the sun is in a plane other than perpendicular to the direction of the prism rows, its radiation will not impinge on the rows of prisms at the optimum angle for which the prisms were designed, as shown in the drawings in those patent documents. According to the present invention, the rows could be aligned at any angle with respect to a window edge, that angle being calculated such that the optimum desired transmission characteristics as a function of the sun's path across the sky, are obtained.

At the same time, the angular orientation of the arrays can preferably reduce distortion. If the room in which the window is installed is to be utilized for only part of the day, then the average inclination and direction of the sun is preferably taken over the hours of use only.

Though the invention is operable with any geometric form in the rows, and has been thuswise described, since prismatic cross-sectional forms are the most generally used forms in such windows, the variously preferred embodiments of the invention are generally described and claimed in terms of prismatic rows, and more preferably, in terms of prismatic rows with triangular cross-sections. It is to be understand, however, that the invention is not meant to be limited to such forms, but is applicable to any geometric form, wherever relevant.

According to a second preferred embodiment of the present invention, there is provided a method for optimizing the geometric shape and size of geometric forms or prismatic forms of rows on an angularly dependent transmissive window surface, and for optimizing the direction of those rows, in order to provide optimum control of the solar radiation transmitted through the window. The optimization method takes into account factors which include the latitude of the building where the windows are to be installed, the direction which the window faces and the inclination of the window. The inclination factor could also be used to take into account windows installed in the roof of a room, where the direction of the prismatic arrays, as well as the configuration, would influence the light transmissivity through the window.

The first two factors determine the elevation and bearing of the sun relative to the window as a function of the season of the year and of the time of the day respectively, and the third qualifies the first two factors on the basis of architectural, aesthetic or utilitarian preferences. All of these factors may be taken into account, according to the method of this preferred embodiment of the present invention, in designing the shape of the prisms used in the surface, and their size and orientation, in order to optimize the light transmission for differently exposed sides of the building and differently inclined windows. In U. S. Patent No. 4,519,675 mentioned above, there is described the use of differently configured prisms for handling sunlight incident at different angles.

Mention is also made of the fact that the angle of solar incidence is different between summer and winter. But no suggestion or mention is made of a method of selecting a prismatic array surface with different transmissive properties, by virtue of their having different angles, different shapes or different orientations, for windows facing different directions, in order to utilize the most energy efficient design for different windows in the building.

According to a third preferred embodiment of the present invention, the parameters of the elements of the window, including the shapes of the prismatic profiles, are preferably selected such that distortions of the light transmitted through the window are minimized. The level of distortion present is a function of a number of factors, including: (i) the angle of view; (ii) the gap between the surfaces, for a window constructed of two surfaces as described below; (iii) the number of facets of the prismatic shape used; and (iv) the angles between the facets of the prismatic shape used. Factors (iii) and (iv) are more important for single layer windows, or for double windows with a comparatively large gap between them.

Most of these factors are also operative in determining the solar transmission of the surface or surfaces. According to this embodiment of the present invention, the architect of the building is provided with a design tool, which enables him to select the desired trade-off between uniform solar radiation as a function of time, and visual distortion through the window. This is achieved by means of a weighting parameter which is assigned to each of these two factors, according to the relative importance of the two factors, and which is taken into account in the iterative optimization process.

According to this preferred method, the optimum prism configuration is chosen, according to the latitude and orientation of the window, so as also to reduce residual distortion through the window to the minimal level possible according to these parameters. This advantage arises because panels designed for transmitting high angles of incidence have a higher level of visual distortion than those for transmitting lower angles of incidence. The level of distortion is given a weighted value, and is also taken into account together with the weighted value given to the transmission modulation efficiency in the method of the second embodiment described above.

The result is a preferred method whereby the parameters of the prismatic array used in constructing the desired window are chosen as a result of an optimization process which simultaneously both improves the transmission characteristics and reduces the residual distortion characteristics, both according to the location, direction and inclination of the window.

According to another preferred embodiment of this aspect of the present invention, the included angles of the prisms are selected such that the transmission characteristic through the window are such that the transmitted light intensity shows less variation during the course of a day, than prior art prismatic array windows. In the prior art there is only described the use of right angled prisms, which result in a large diurnal variation of transmitted intensity..

According to this preferred embodiment of the present invention, the use of prisms with angles other than 90 , if the prismatic angles are correctly chosen, results in substantially more uniform illumination during the course of the day.

Furthermore, the angular orientation of the rows of the prisms can also be aligned at an angle which will give optimum optical transmission uniformity. According to a further preferred embodiment of the present invention, the optimization procedure can be adapted so that overall transmission level is minimal in the summer and maximal in the winter, or has any other desired characteristic as a function of time.

According to a fourth preferred embodiment of the present invention, the prismatic shapes are embossed onto the surface of a plastic window material by means of a specially designed embossing tool comprising a number of embossing discs, whose edge angle and inclination are such as to provide the correct predefined prism angles with a minimum of rounding of the bottoms of the grooves between prisms. Such rounded groove bottoms are dead space with respect to optical transmission through the window, causing additional optical distortion of the light passing through them.

According to a fifth preferred embodiment of the present invention, the prismatic shapes in the surface are of forms different to the hitherto used triangular prisms. Examples of such forms are trapezoidal prisms, or prisms of pyramidal form. According to these embodiments, additional degrees of freedom are enabled for optimization of the parameters for providing the desired range of transmission angles.

According to a sixth preferred embodiment of the present invention, a method is provided of reducing angular distortion from an angularly dependent transmission window, by the use of a pair of prismatic array surfaces, the prisms having a selected geometric form, in a double-paned window construction. Such a double-paned construction has a number of additional advantages over the prior art single surface window. The use of two surfaces with angularly dependent transmission provides an additional degree of freedom in the design of optimum range of transmission angles with minimum visual distortion.

The use of a complementary double layer of prismatic structures has been first proposed in German Published Patent Application No. 1,171,370, and thereafter in U. S. Patent No. 4,519,675, in order to correct the lateral shift of transmitted light incident in a plane perpendicular to the direction of the prismatic structure array. Although this shift is termed a distortion in Patent No. 4,519,675, such a shift simply moves the whole image laterally, and does not generally distort the subjective view in that direction through the window. It is not thus strictly a distortion. However, no mention is made in that prior art of a far more serious and a real distortion, resulting from light transmitted in a plane not perpendicular to the direction of the prismatic arrays. Under such conditions, the image becomes distorted, such that, for instance, a square becomes a parallelogram.

Such distortions are significantly more serious than the lateral shifts considered, because they result in angular shape and/or dimensional distortion of objects viewed. The use of a complementary double layer of prismatic structures is operative to reduce such"non-perpendicular"distortions to acceptable proportions. The extent to which such distortion can be reduced is dependent on the distance between the surfaces, the angle of the viewer's line of sight through the window, and the form of the prismatic shapes, a trapezoid, for instance, being more difficult to correct than a triangular prism, and a row of pyramidal shapes being more difficult to correct than a single prismatic form along the length of the array row.

According to this preferred embodiment of the present invention, the method is equally effective whether the direction of the prismatic arrays are horizontal, or whether they are tilted with respect to the horizontal, as described in the first preferred embodiment above.

In all of the prior art embodiments of double layers of prismatic structures, the direction of the rows prismatic profiles on one surface are parallel to those on the second surface, and in general have complementary profiles, the two layers mutually interacting optically to reduce distortion. According to a further preferred embodiment of the present invention, the two layers, each of which may itself be aligned at an arbitrary angle to an edge of the window in which it is installed, are aligned at an angle to each other. Furthermore, each of the layers can preferably have a different profile, each having its own preselected optical properties, thereby even further expanding the possibilities of custom designing the window to provide specific performance parameters.

However, since such a double panel with prismatic ridges lying at different angles cannot be manufactured by the commonly used extrusion methods, a novel method of double prismatic panel construction is disclosed, in which the prismatic panels are made separately by an injection molding process, and are supported on a central honeycomb support structure, preferably with fixing points built in. This provides a double panel of higher strength than equivalent prior art panels manufactured by extrusion, and is of low weight and low material use, is easily installed, and makes possible the insertion of panels of different design on each side of the support.

Furthermore, an anti-reflection layer can preferably be incorporated between the two surfaces, or on one or both of them, in order to prevent multiple image effects from disturbing the visual quality through the window. In addition, the use of a thin optical film on one or both of the surfaces can provide enhancement of the angularly dependent transmission effect, as described in co-pending Israel Patent Application No. 140,310, by the applicant of the present invention. Alternatively and preferably, one or more thin film stacks can be used to provide spectral filtering of the transmitted light, either by limiting the transmission of the infra-red light, which causes heating of the building interior without adding any visual advantage, or to correct any color bias caused by the angularly dependent thin film coating mentioned above.

The thin films can preferably be applied either to a sheet incorporating the angularly dependent transmission structure, or on a separate layer attached or in proximity to it.

Furthermore, the incorporation of an anti-fogging agent in the plastic sheets enables the window to be constructed with less rigorous sealing requirements than prior art double windows.

In accordance with yet another preferred embodiment of the present invention, there is provided a window with angularly dependent optical transmission properties, comprising a first transmissive surface with an array thereon consisting of rows of geometric forms, the geometric forms being such as to internally reflect light incident on the surface over a predetermined range of angles, and wherein the rows are aligned at any angle with respect to a window edge. This angle is preferably calculated such that the angularly dependent light transmission properties are optimized.

There is further provided in accordance with still other preferred embodiments of the present invention, a window as described above and wherein the geometric forms are prisms of triangular cross-section, or of trapezoidal cross-section or are of pyramidal shape.

In accordance with a further preferred embodiment of the present invention, there is also provided a window as described above and also comprising a second transmissive surface disposed in proximity to the first transmissive surface, wherein the second transmissive surface also has an array thereon comprising rows of geometric form. The shapes and alignment of these rows may preferably be complementary to those of the first transmissive surface.

In accordance with yet further preferred embodiments of the present invention, any of the windows described above may also include at least one thin optical film on a surface, to further modify the optical properties of the window.

The at least one thin optical film may preferably be an anti-reflective coating, or may have angularly dependent transmission properties and be operative to enhance the angularly dependent transmission properties of the window.

Furthermore, the at least one thin optical film may have preferential spectral transmissive properties, which may be operative to attenuate the transmission of infra-red radiation through the window.

There is even further provided in accordance with a preferred embodiment of the present invention, a method of determining an optimized prism array configuration for use in an angularly dependent transmissive window, comprising the steps of : (a) calculating the solar radiation incident on the window, based on the latitude of the window, the window orientation and the inclination of the window to the vertical, (b) providing a library of prism array configurations, (c) selecting a prism array configuration from the library, (d) calculating the transmission function of the selected configuration, (e) calculating the transmission through the array of the solar radiation incident on the window, (f) determining whether the transmission is less than a predetermined level, and (g) repeating steps (c), (e) and (f)

if the transmission is not less than the predetermined level. Furthermore, in accordance with yet another preferred embodiment of the present invention, the geometric configuration of the prism array is preferably defined by the prism shape, prism orientation, and prism size.

In accordance with a further preferred embodiment of the present invention, in the method mentioned above, the predetermined level may preferably comprise an integrated level of transmitted solar radiation during the day, or of an instant level of transmitted solar radiation.

In accordance with yet another preferred embodiment of the present invention, there is provided a method of determining a distortion-optimized prism array configuration for use in an angularly dependent transmissive window, comprising the steps of : (a) calculating the viewing angle through the window, from the location of the viewer and the inclination of the window to the vertical, (b) providing a library of prism array configurations, (c) selecting a prism array configuration from the library, (d) calculating the distortion of light transmitted through the selected configuration, (e) determining whether the distortion is less than a predetermined level, and (f) repeating steps (c), (d) and (e) if the transmission is not less than the predetermined level.

In accordance with still another preferred embodiment of the present invention, in the method described above, the prism array configuration may consist of at least one of prism shape, prism orientation, prism size and gap between the two surfaces containing the prisms.

There is further provided in accordance with still another preferred embodiment of the present invention a method of reducing distortion caused during the passage of light through a first surface having angularly dependent transmissive properties by virtue of an array of rows of prismatic form on the surface, comprising the step of adding a second transmissive surface disposed in proximity to the first surface, the second transmissive surface comprising a prismatic array having a shape and alignment complementary to that of the first surface, wherein the method is operative to reduce distortion arising from the passage of light through the surface at an angle which is not perpendicular to the direction of the rows of prismatic form.

Furthermore, in accordance with yet another preferred embodiment of the present invention, there is provided a window with angularly dependent optical transmission properties, comprising a first transmissive surface with an array thereon comprising prismatic rows of trapezoidal cross-section, whose form is such that the fraction of light incident on the surface that is transmitted depends on the inclination and bearing of the incident light.

In accordance with a further preferred embodiment of the present invention, there is also provided a window as described above and also comprising a second transmissive surface disposed in close proximity to the first transmissive surface, wherein the second transmissive surface has an array thereon comprising prismatic rows of trapezoidal cross-section having a shape and alignment complementary to those of the first transmissive surface.

There is further provided in accordance with still another preferred embodiment of the present invention a method of increasing the uniformity of solar transmission through a window, comprising the steps of providing on a first surface of the window an array of parallel rows of prismatic form, disposing in proximity to the first surface a second transmissive surface with an array of parallel rows of prismatic form, and optimizing the uniformity of solar transmission through the window over a selected period of time by iteratively varying at least one parameter of the rows of prismatic form, or the prismatic forms themselves. Preferably, if the prismatic form has a triangular cross-section, the parameter may be the apex angle of the triangular cross section.

The second transmissive surface may preferably comprise an array of parallel rows of prismatic form having a shape and alignment complementary to that of the first surface. The step of optimizing the uniformity of solar transmission through the window over a selected period of time may preferably be performed alternatively or additionally by iteratively varying the orientation of the array of parallel rows of prismatic form. Additionally or alternatively, any of the above-mentioned iterative methods may be adapted to provide optimally desired levels of transmission during different seasons or times of day.

In accordance with yet another preferred embodiment of the present invention, there is also provided a window with improved solar transmission uniformity comprising a first transmissive surface with an array thereon comprising rows of prismatic forms having a triangular cross-section, and a second transmissive surface with an array thereon comprising rows of prismatic forms having a triangular cross-section, the second surface being aligned in proximity to the first surface, wherein the apex angle of at least one of the triangular cross-sections is iteratively varied such that the uniformity of solar transmission through the window over a selected period of time is optimized.

The apex angle is preferably between 90 and 100 , more preferably between 93 and 97 , and even more preferably approximately 95 .

BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:
Fig. 1A shows a schematic flow chart of a method for determining an optimized prism configuration for use in optimizing the solar transmission according to the geographic location, direction and inclination of the window in which the prism configuration is used;
Fig. 1B shows a schematic flow chart of a method for determining the optimized prism configuration for use in minimizing the visual distortion through the surface according to the latitude, orientation and inclination of the window in which the prism configuration is used, and, when more than one layer is used, according to the gap between the layers;

Figs. 2A and 2B are schematic illustrations of prismatic arrays on a window, showing in Fig. 2A, a prior art window with the direction of the prismatic rows aligned parallel to a side of the window, and in Fig. 2B, a window according to a preferred embodiment of the present invention, with the array at an arbitrary angle to a side of the window;
Figs. 3A to 3C are graphs showing the solar transmission characteristics of a prior art window, such as that shown in Fig. 2A, during the course of a day in mid-summer, at the equinox and in mid-winter respectively;
Figs. 4A to 4C are graphs showing the solar transmission characteristics of a window, such as that shown in Fig. 2B, constructed and operative according to a preferred embodiment of the present invention, during the course of a day for the longest day of the year, the equinox and the shortest day respectively.

Figs. 5A to 5F are graphs showing the daily solar transmission characteristics of a window having double prismatic panels, constructed and operative according to a preferred embodiment of the present invention, for two different latitudes and for the longest day, the equinox and the shortest day;

Figs. 6A and 6B are schematic drawings of a window constructed from a pair of prismatically structured sheets, according to a preferred embodiment of the present invention;
Figs. 7A to 7F show computer simulation results of the optical transmission distortion characteristics of various windows, both prior art and according to preferred embodiments of the present invention, and wherein the incident light is not necessarily normal to the window;
Fig. 8 shows a window pane of the type displayed in Fig. 6A, but also including a multi-layer thin film on its smooth surface to further modify the transmissive properties of the window;

Fig. 9 is a schematic representation of a double-paneled window, constructed according to a further preferred embodiment of the present invention, each panel having a prismatic structure inclined at a different angle to the other, such that the prismatic ridges in the top panel are not parallel to those in the bottom panel; and
Fig. 10 is a schematic drawing of a window constructed according to a further preferred embodiment of the present invention, of two separate injection molded prismatic panels, each with its characteristic prismatic structure and angle, each firmly attached to a different side of the support framework.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is now made to Figs. 1A and 1B, which illustrate schematic flow charts used for methods, according to preferred embodiments of the present invention, for determining the parameters needed for constructing various windows according to the present invention. Fig. 1A illustrates a schematic flow chart of a preferred method for determining the optimum prism configuration and orientation for use according to the latitude, orientation and inclination of the window in which the prism configuration is used. A number of inputs are made by the user. In step 10, the location, expressed as the latitude of the building is input. In step 11, a desired date is input.

In step 12, the sun's path is calculated from this input data, and in step 13, the inclination and azimuthal angles of the sun are calculated as a function of the time of day for each day of the year. In step 14 and 15, the window azimuthal direction and inclination are respectively input.

In step 16, these window-related data are combined with the data about the sun's position during the course of the day to output a table of solar radiation incident on the window for the entire day.

This data is now used to determine the effect of various prism configurations on the solar transmission through the window for the whole of the year. In order to achieve this, the type of prism profile is input in step 17, and its characteristics stored in memory in a library of prism configurations at location 18. In step 19, the orientation of the rows of prisms is input, since this has a major effect on the solar transmission through the arrays of prisms. In step 20, the incident solar radiation, described in terms of its intensity and incident direction, is inserted into the angular transmission function of the selected prism configuration and orientation. The result is an output function, provided in step 21, of hour-by-hour, daily solar transmission through the window for each day of the year.

This graph is then compared in step 22 with the solar transmission desired of the window. If the result does not reach expectations, and the integrated solar radiation penetrating the window is greater than the level desired, then in step 24, a new prism configuration is chosen, the selection re-entered into steps 17 and 19, and the transmission results are recalculated according to the flow chart shown. The prism type selected in step 17 and the prismatic array orientation selected in step 19 are changed iteratively, in a manner which ensures convergence towards the desired result. When the desired solar transmission is achieved, the resulting window design is output at step 25.

It is to be understood that the definition of the desired solar transmission can be a function of the total integrated daily transmission, or a function which ensures that the instantaneous transmission at any time during the day does not exceed a preset level, or any combination thereof.

Reference is now made to Fig. 1B, which is a schematic illustration of a flow chart of a method, according to another preferred embodiment of the present invention, for determining the optimum prism configuration for minimizing distortion in the light transmitted through the window. The distortion through a prismatic array of the type described in this application, is dependent on at least four parameters: (i) the angle of view ; (ii) for a window constructed of two complementary surfaces as described below, the gap between the surfaces, as is known from the prior art ; (iii) the number of facets of the prismatic shape used ; and (iv) the angles between the facets of the prismatic shape used.

Factors (iii) and (iv) are more important for single layer windows, or for double windows with a comparatively large gap between them. The distortion can be minimized by the use of a double prismatic structure with a very small gap between the arrays. The distortion produced in viewing through the prisms is dependent on these factors in the following ways. The smaller the angles of the prisms, the greater the distortion. The larger the gap between the layers, the greater the distortion. The greater the angle of view from the vertical, the greater the distortion.

A number of inputs are made by the user in the method illustrated by the flow chart of Fig. 1A. In step 30, the mostly used viewing location in the room is entered, which together with the window inclination, 31, determines the angle of view 32 through the window. The parameters of the window are input at steps 33, 34 and 35. At step 33, the orientation of the prismatic arrays in the window are entered. At step 34, the characteristics of the prism profiles are entered. At step 35, if the window is of a double complementary prismatic layer type, the gap between the layers is entered.

The three window parameters and the viewing angle are used in calculating, in step 36, the distortion level expected from that combination. In step 37, this distortion level is compared with the desired maximum distortion level, and if found to be less than the desired level, the parameters are output at step 38 for use in designing the window. If the distortion level is still too high, the window configuration parameters are amended and the new selection re-entered into steps 33,34 and 35, and the distortion level is recalculated at step 36 according to the flow chart shown. The prismatic array orientation selected in step 33, the prism type selected in step 34 and the window layer gap selected in step 35 are changed iteratively, in a manner which ensures convergence towards the desired result.

Since the effect of changing the window parameters also effects the transmission characteristics of the window, it is not generally possible to optimize both the distortion, according to the flow chart of Fig. 1B, and the solar radiation correction, according to the flow chart of Fig. 1A simultaneously. According to a further preferred embodiment of the present invention, each of these results is given a weighting factor, according to its importance in the application or situation on hand, and the combined weighted result is optimized by running the procedures in both flow charts alternately and iteratively, until the window design with the desired combination of properties is obtained.

Reference is now made to Fig. 2A, which is a schematic illustration of a prior art window 40, with an array of prismatic shapes 42 providing it with angularly dependent light transmission. The rows of prisms are aligned parallel to a window edge. Such a prior art window is shown in Fig. 2A installed in a wall whose orientation is such that the direction of a light ray 43 from the sun 44 at local noon, subtends on the wall of the building in which the window is installed, an angle 0 to the vertical 45. In general, the light is not incident on the rows of the array of such a prior art window from a direction normal to the direction of the rows of the array, and consequently, the window does not operate at its optimum efficiency in terms of solar radiation modification performance.

Reference is now made to Fig. 2B, which is a schematic illustration of a window 46, according to a preferred embodiment of the present invention. The window provides angularly dependent light transmission, by means of an array of prismatic shapes 48, but, unlike prior art arrays, the array is aligned at an angle to a window edge, such that the projection onto the window plane of the direction of the sun at its highest point 44 preferably subtends, for instance an angle of 90 with the direction of the rows of the array. The array thus operates at its optimum design efficiency when the sun is at its highest point, and consequently also averaged over the whole of the solar radiation"day".

It is to be understood that the preferred embodiment shown in Fig. 2B is only an example of the application of this aspect of the present invention, and that in a similar manner, the alignment of the array direction can be selected to provide optimum performance with regard to the sun's position, at any time of the day, according to the requirements of the building. Thus, for instance, if a window in a particular room faces south, but the room is only in use in the mornings, the array could be aligned such that it is correctly orientated with respect to the average direction of the sun during those hours of use.

Furthermore, although Fig. 2B shows a window installed in a wall, it is to be understood that this preferred embodiment of the invention can be equally applied to windows installed in roofs as skylights or in glasshouses, or in sloping walls inclined at an angle to the vertical.

Reference is now made to Figs. 3A to 3C, which are graphs showing the calculated solar transmission characteristics of a prior art window, such as that shown in Fig. 2A, during the course of a day in mid-summer, at the equinox and in mid-winter respectively. The results were calculated using the Advanced
Systems Analysis Program (ASAPTM) ray tracing program, supplied by Breault
Research Organization Inc. of Tucson, Arizona. The results are shown for the latitude of Tel Aviv, being 32 North. The window incorporates an array of 30 -90 -60 prisms, aligned horizontally across the width of the window, as depicted in Fig. 2A. The window faces due West, and is vertically inclined.

The graphs in Figs. 3A to 3C show, by means of the dotted curve, the solar radiation transmitted through the window during the course of the day, at different times of the year. As is observed, since the window faces west, the sun shines into it only during the afternoon. For comparison purposes, to show the efficiency of the window, the incident solar radiation is also plotted on the same graphs, as a solid line.

Fig. 3A shows the solar radiation transmission profile for June 21, i. e. the longest day of the year. The total integrated radiant energy transmitted during the day through this prior art window is 6,800 BTU per square meter of window. For comparison purposes, the total thermal solar thermal flux, as measured through a plain glass window, is 9,700 BTU per square meter, meaning that this prior art window transmits 70% of the incident input thermal flux.

Fig. 3B shows the solar radiation transmission profile for September 21, i. e. the equinox. The total integrated heat input over the day through this prior art window is 5,400 BTU per square meter of window, compared with 8,300 BTU per square meter of total incident thermal solar flux. The window thus transmits 65% of the incident thermal flux.

Fig. 3C shows the solar radiation transmission profile for December 21, i. e. the shortest day of the year. The total integrated heat input over the day through this prior art window is 1,900 BTU per square meter of window, compared with 4,700 BTU per square meter of total thermal solar thermal flux.

The window thus transmits 40% of the incident solar thermal flux.

Reference is now made to Figs. 4A to 4C, which are graphs showing the calculated solar transmission characteristics of a window, such as that shown in
Fig. 2B, constructed and operative according to a preferred embodiment of the present invention. The graphs show the transmission during the course of a day in mid-summer, at the equinox and in mid-winter respectively. The results are shown for the latitude of Tel Aviv, being 32 North. The window incorporates an array of 30 -90 -60 prisms, whose rows are aligned in this preferred embodiment at an angle of 70 to the horizontal, such that they have a more advantageous alignment with respect to the average direction of the sun. The window faces due
West, and is vertically inclined.

Fig. 4A shows the solar radiation transmission profile for June 21, i. e. the longest day of the year. The total integrated heat input over the day through this window is 2,700 BTU per square meter of window, meaning that the window according to this embodiment of the present invention reduces the transmitted flux to only 28% of its incident value. This is a significant improvement over the prior art window shown in Fig. 3A. Furthermore, the graph shows that the thermal input flux is uniformly low, unlike the prior art window, wherein between the hours of 12.00 noon and approximately 3.30 p. m., the transmitted flux is virtually unreduced from the incident flux.

Fig. 4B shows the solar radiation transmission profile for September 21, i. e. the equinox. The total integrated heat input over the day through this window is 5,000 BTU per square meter of window, a reduction of 60% compared with the incident solar flux. This reduction is slightly more advantageous than the prior art window shown in Fig. 3B, and the shape of the intensity profile is generally similar.

Fig. 4C shows the solar radiation transmission profile for December 21, i. e. the shortest day of the year. The total integrated heat input over the day through this window is 4,000 BTU per square meter of window, compared with 4,700 BTU per square meter of total thermal solar thermal flux. The window according to this embodiment of the present invention thus transmits 85% of the incident solar thermal flux, and in the early hours of the afternoon, from 12.00 noon to approximately 3.30 p. m., the window transmits almost all of the incident sunlight. This performance is a very significant improvement over that of the prior art window shown in Fig. 3C, since in the winter months, the window should be operative to attenuate the incident sunlight as little as possible, in order to utilize the sun's thermal energy as much as possible.

From the graphs shown in Figs. 4A to 4C, it is evident that a window constructed according to the present invention, with preferential orientation of its prismatic arrays, provides significant advantages over prior art windows in terms of energy transmission, both in summer to save cooling costs, and in winter to save heating costs.

Reference is now made to Figs. 5A to 5E which are graphs showing the diurnal solar transmission characteristics of a window, constructed and operative according to a preferred embodiment of the present invention, having a double layer of triangular prismatic structures, with angles of 35 -95 -50 . Graphs are shown for different azimuthal alignments of the window and at different times of the year. In all of the graphs, the results are given for the case of the rows of prismatic structures aligned vertically, i. e. from top to bottom of the window.

The prismatic angles used, 35 -95 -50 , and the alignment of the rows of triangular prismatic structures were selected by means of an optical design optimization program, in which the angles of the prisms were varied in order to obtain optimum transmission uniformity during the course of the day. A preferred method of construction of such an array of double prismatic surfaces is described herein below. The window prismatic profiles are manufactured of an acrylic material having a refractive index of 1.65. In all of the graphs, the window tilt is 90 to the horizontal, i. e. the window is located in a vertical wall. The results shown are only meant to be one preferred example of an optimization procedure performed to provide optimum transmission uniformity in such a double window.

According to a further preferred embodiment of the present invention, the angular orientation of the prismatic rows can also be varied to optimize the transmission uniformity for each particular location and window direction.

In Figs. 5A to 5C are shown, by way of example, the transmission at the equinox for the latitude of Tel Aviv. In Fig. 5A, the results are shown for a window facing south. The transmitted solar radiation is reduced by a factor of 70%. However, more significant for this preferred embodiment is the fact that the solar radiation through the window is comparatively uniform during the course of the day. This uniformity of illumination achieved in this embodiment is especially advantageous since it enables significant savings to be made in the provision of light and heat, in that it significantly reduces the level of thermal heating during the middle of the day, while maintaining a good level of light at the beginning and end of the day. Similarly dramatic improvements in the uniformity of illumination are attained for such windows facing other directions.

Thus, for instance, Fig. 5B shows the results for such a window facing east, with an 87% reduction in transmission, and Fig. 5C for such a window facing west, with an 88% reduction in transmission. As is observed, there is good uniformity of illumination in both these examples.

In a similar manner, Figs. 5D to 5F show the results of using the same window design at the latitude of Madrid, and on June 21. Fig. 5D is for the window facing south, Fig. 5E for that facing east, and Fig. 5F, facing west. The reduction in total solar flux through the window is calculated as ranging from 83 to 84% in all three azimuthal cases, and the uniformity obtained is good in all three cases.

The invention has so far been described in terms of triangular prismatic shapes. It is to be understood though, that prismatic shapes of any geometric form may preferably be used for the invention, such as trapezoidal prismatic shapes.

Reference is now made to Figs. 6A and 6B, which are schematic drawings of a window constructed of a pair of prismatically structured sheets, according to yet another preferred embodiment of the present invention. Fig. 6A is an overall isometric view of such a window, while Fig. 6B is a cross section showing the two transparent window surfaces 80,82, facing each other. In the embodiment shown in Fig. 6B, the window pane material is glass 84, while the prismatic structure which provides the angularly dependent transmission is in the form of a thin plastic sheet with embossed prisms 86, attached to the glass pane. The two facing complementary prism structures co-operate optically to provide an optimum range of transmission angles with minimum optical distortion.

The space between the panes can preferably be filled with an inert gas, such as argon, and the material of the panes themselves, can preferably include an anti-fogging agent to maintain a clear condensation-free interior between the panes. In order for this to be effective, the panes must have a gas-tight seal between them.

Reference is now made to Figs. 7A to 7F, which show the results obtained from optical simulations on windows with angularly dependent transmission properties. The simulations were performed using the Advanced Systems
Analysis Program (ASP) ray tracing program, supplied by Breault Research
Organization Inc. of Tucson, Arizona. A square shaped frame is used as the luminous source, and the effect of distortion in passage of the light from the source through the various windows tested is observed qualitatively on the images produced. Figs. 7A to 7F are direct reproductions of the images on the monitor of the computer on which the results were calculated, and the cross lines appearing have no significance.

Fig. 7A shows the effect of the transmission of light through a regular window composed of two flat panes, with the illumination coming from a direction at a normal to the plane of the window. As is observed, there is no significant geometric distortion.

Fig. 7B shows the effect of the illumination transmitted through the window of Fig. 7A but at an azimuthal angle of 5 , and an elevation angle of 4 , making a total angle of 6.5 to the normal to the window surface. As is observed, there is no significant geometric distortion.

Fig. 7C shows the effect of the illumination transmitted at normal incidence through a prior art window with a single layer of transparent sheet including a prismatic array whose prisms are triangular with angles of 35-95-50 .

The image is somewhat distorted, being shortened in the azimuthal direction, but remains rectangular.

Fig. 7D shows the effect of the illumination transmitted through the prior art window of Fig. 7C, but at an azimuthal angle of 5 , and an elevation angle of 4 . The image is severely distorted, with the square source being transmitted as a parallelogram shape.

Fig. 7E shows the effect of the illumination transmitted at normal incidence through a window according to a preferred embodiment of the present invention, such as that shown in Figs. 6A and 6B, the window being composed of two layers of transparent sheet, each including a complementary prismatic array whose prisms are triangular with angles of 35-95-50 . It is observed that there is no significant geometric distortion, but that the image is slightly more diffuse, as a result of the increased number of reflections which the rays undergo in passing through a double set of prisms.

Fig. 7F shows the effect of the illumination transmitted through the window of Fig. 7E, but at an azimuthal angle of 5 , and an elevation angle of 4 .

It is observed that the image is somewhat distorted, being lengthened in the azimuthal direction, but remaining rectangular. This distortion is significantly less than that resulting from similar off-normal incident illumination on a single layered prismatic array.

Reference is now made to Fig. 8, which shows a single window pane of the type used to construct a window such as that displayed in Fig. 6A, including a multi-layer thin film 90 on the smooth surface, according to a further embodiment of the present invention. The thin film can be operative as an anti-reflective coating, thereby reducing the production of ghost images from multiple reflection between the two panes in the embodiment of Fig. 6A.

Alternatively and preferably, the thin film coating can provide enhancement of the angularly dependent transmission effect, or it can be used to provide spectral filtering of the transmitted light, either by limiting the transmission of the infra-red light, which causes heating of the building interior without adding any visual advantage, to correct any color bias caused by the angularly dependent thin film coating mentioned above.

Reference is now made to Fig. 9, which is a schematic representation of a double-paneled window, constructed according to a further preferred embodiment of the present invention, each panel having a prismatic structure inclined at a different angle to the other, such that the prismatic ridges in the top panel 100 are not parallel to those in the bottom panel 102. The use of rows of prismatic structures inclined at different angles to each other in a double-paned window provides a further degree of freedom in designing the optimum or desired transmission characteristics of the window. The prismatic profile of the prismatic ridges in the top panel can preferably even be of a different shape to those in the bottom panel.

In prior art windows, with the direction of the prismatic rows parallel to a window side, it is simple and cost-effective to manufacture the prismatic panels by means of an extrusion process, with the rows of prisms running along the length of the extruded sheet. A singly extruded sleeve consisting of both prismatic panels and the side walls joining the panels is extruded in a continuously long flow, and the length is cut according to the dimensions of the window required. The ends are then sealed by adhesively inserting sections of a profile which fits into the cross sectional interior space of the window. It is also possible to extrude support ribs at intervals inside the sleeve, for use in very wide window panels which require support across their width.

According to the preferred embodiments of the present invention, wherein the direction of the prismatic rows is not parallel to the direction of a window edge, this extrusion production method is not possible. Therefore, another low cost method must be devised for producing the panels and assembling them at the correct spacing with respect to each other.

Reference is now made to Fig. 10, which illustrates schematically a window having directionally amended transmissive properties, constructed according to a further preferred embodiment of the present invention. The window shown in Fig. 10 is constructed of two separate prismatic panels 110, 112, each with its characteristic prismatic structure and angles, each firmly attached to a different side of a framework 114. The profile of the framework 114 is preferably provided with grooves 116, into which integral lip profiles 118 at the edges of the panels can be inserted and adhesively joined to provide a gas-tight join. To provide additional strength and gas-tightness, the edges of the panels can preferably also be supplied with an internal lip 120, which is stuck to the inside of the framework profile.

Gas tightness is important to avoid the ingress of moisture and dirt, which would reduce the performance of the window, and to prevent the leakage of any inert gas filling provided.

The panels 110,112 are preferably manufactured by an injection molding process, and are preferably made of a polycarbonate or more preferably, of an acrylic material. Acrylic has higher optical transparency, is more UV resistant, attracts dust less and is cheaper than polycarbonate, so is the preferred material for the panels. The support framework 114, is preferably manufactured of an impact resistant plastic, such as a glass-fiber reinforced plastic. This framework structure can be provided with reinforced mounting points to simplify the installation process. By this means, the double prismatic panel of the present invention is manufactured with low weight, high impact resistance and is capable of simple installation.

Because the internal framework is visible through the panels, this method of construction is generally only suitable for smaller windows, where the framework is only required at the edges, or for large area windows for use as environmentally corrective windows, such as in skylights, in greenhouses, or in the roofs of swimming pools, where the view through the window is of secondary importance to its thermal radiation transmissive properties. In such large windows, a complete network of supporting framework is preferably provided across the entire area of the window, supplying support to the prismatic panels as necessary.

The use of an injection molded support framework has a number of advantages over prior art extruded integral frames. Firstly, it is possible to build into the framework protrusions and other features which are non parallel to the direction of extrusion. By this means, areas or regions having enlarged dimensions can be incorporated into the framework for use as mounting points. In addition, in order to provide higher structural strength to the end product, it is possible to make the support framework of a plastic incorporating reinforcement means, such as glass fiber reinforcement.

The method of construction used in double panel windows according to the above-mentioned preferred embodiments of the present invention, namely the use of injection molded outer panels supported and sealed onto a support framework preferably manufactured of a high strength, impact resistant, injection molded plastic, may also be advantageously used for the construction of panels for general use, such as in walls and dividers, where there is required a low cost, high impact resistant wall with possibly superior insulating properties engendered by the sealed double wall structure of the present invention.

It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove.

Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.

Claims

CLAIMS We claim: 1. A window with angularly dependent optical transmission properties, comprising a first transmissive surface with an array thereon comprising rows of geometric form, said geometric form being such as to internally reflect light incident on said surface over a predetermined range of angles, and wherein said rows are aligned at any angle with respect to an edge of said window.

2. A window according to claim 1 and wherein said angle is such that said angularly dependent light transmission properties are optimized according to the directions of incidence of said light.

3. A window according to claim 1 and wherein said rows of geometric form are rows of prisms of triangular cross-section.

4. A window according to claim 1 and wherein said rows of geometric form are rows of prisms of trapezoidal cross-section.

5. A window according to claim 1 and wherein said rows of geometric form are rows of pyramidal shapes.

6. A window according to any of claims 1 to 5 and also comprising a second transmissive surface disposed in proximity to said first transmissive surface, said second transmissive surface also having thereon an array comprising rows of geometric form.

7. A window according to claim 6 and wherein said rows of geometric form in said array on said second transmissive surface are disposed complementarily to those of said first transmissive surface.

8. A window according to any of claims 1 to 6 and also comprising a second transmissive surface disposed in proximity to said first transmissive surface, said second transmissive surface having an array thereon comprising rows of geometric form, and wherein said rows on said second transmissive surface are aligned at an angle to said rows of said first transmissive surface.

9. A window according to any of claims 1 to 8 and also comprising at least one thin optical film on a surface of said window, to further modify the optical properties of said window.

10. A window according to claim 9 and wherein said at least one thin optical film is an anti-reflective coating.

11. A window according to claim 9 and wherein said at least one thin optical film has angularly dependent transmission properties, and is operative to enhance the angularly dependent transmission properties of said window.

12. A window according to claim 9 and wherein said at least one thin optical film has preferential spectral transmissive properties.

13. A window according to claim 12 and wherein said preferential spectral transmissive properties are operative to attenuate the transmission of infra-red radiation through said window.

14. A method of determining an optimized prism array configuration for use in an angularly dependent transmissive window, comprising the steps of : (a) calculating the solar radiation incident on said window, from the latitude of the location of the window, the geographical direction which the window faces and the inclination of the window to the vertical; (b) providing a library of prism array configurations; (c) selecting a prism array configuration from said library; (d) calculating the transmission function of said selected configuration; (e) calculating the transmission through said array of said solar radiation incident on said window;

(f) determining whether said transmission is less than a predetermined level; and (g) repeating steps (c), (e) and (f) if said transmission is not less than said predetermined level.

15. The method of claim 14 and wherein said prism array configuration comprises at least one of prism shape, prism orientation, and prism size.

16. The method of claim 14 and wherein said predetermined level comprises an integrated level of solar radiation during the day.

17. The method of claim 14 and wherein said predetermined level comprises an instant level of solar radiation.

18. A method of determining a distortion optimized prism array configuration for use in an angularly dependent transmissive window, comprising the steps of : (a) calculating the viewing angle through said window, from the location of the viewer and the inclination of the window to the vertical; (b) providing a library of prism array configurations; (c) selecting a prism array configuration from said library; (d) calculating the distortion of light transmitted through said selected configuration; (e) determining whether said distortion is less than a predetermined level ; and (f) repeating steps (c), (d) and (e) if said transmission is not less than said predetermined level.

19. The method of claim 18 and wherein said prism array configuration comprises at least one of prism shape, prism orientation, prism size and prism array gap.

20. A method of reducing distortion caused during the passage of light through a first surface having angularly dependent transmissive properties by virtue of an array of rows of prismatic form on said surface, comprising the step of adding a second transmissive surface disposed in proximity to said first surface, said second transmissive surface comprising a prismatic array having a shape and alignment complementary to that of said first surface, wherein said method reduces distortion arising from the passage of light through said surface at an angle which is not perpendicular to the direction of said rows of prismatic form.

21. A method of increasing the uniformity of solar transmission through a window, comprising the steps of : providing on a first surface of said window an array of parallel rows of geometric form; disposing in proximity to said first surface, a second transmissive surface with an array of parallel rows of geometric form; and optimizing the uniformity of the intensity of solar transmitted radiation through said window over a selected period of time by iteratively varying at least one parameter of at least one of said surfaces.

22. The method according to claim 21, wherein said parameter is the angle of the rows of at least one of said surfaces relative to a side of said window.

23. The method according to claim 21, wherein said parameter is a property of said geometric form.

24. The method according to claim 21, wherein said geometric form is prismatic form having a triangular cross-section.

25. The method according to claim 24, wherein said step of iteratively varying at least one parameter of at least one of said surfaces comprises the step of varying at least the apex angle of said triangular cross-section of said prismatic form on at least one of said surfaces.

26. A method according to claim 21, and wherein said second transmissive surface comprises an array of parallel rows of geometric form having a shape and alignment complementary to that of said first surface.

27. A method according to claim 26, and wherein said step of optimizing is performed by iteratively varying a parameter of said geometric form of both of said surfaces.

28. A method according to any of claims 21 to 25, and also comprising the step of optimizing the uniformity of solar transmission through said window over a selected period of time by iteratively varying the orientation of at least one of said arrays of parallel rows of prismatic form.

29. A window with improved solar transmission uniformity comprising: a first transmissive surface with an array thereon comprising rows of prismatic forms having a triangular cross-section ; and a second transmissive surface with an array thereon comprising rows of prismatic forms having a triangular cross-section, said second surface being aligned in proximity to said first surface; wherein the apex angle of at least one of said triangular cross-sections is iteratively varied such that the uniformity of the intensity of solar transmitted radiation through said window over a selected period of time is optimized.

30. A window according to claim 29, and wherein said apex angle is between 90 and 100 .

31. A window according to claim 30, and wherein said apex angle is between 93 and 97 .

32. A window according to claim 31, and wherein said apex angle is approximately 95 .

33. A window with improved solar transmission uniformity comprising: a first transmissive surface with an array thereon comprising rows of prismatic forms having a triangular cross-section; and a second transmissive surface with an array thereon comprising rows of prismatic forms having a triangular cross-section, said second surface being aligned in proximity to said first surface; wherein the angle of said rows of prismatic forms on at least one of said surfaces is iteratively varied such that the uniformity of the intensity of solar transmitted radiation through said window over a preselected period of time is optimized.

34. A double paneled window comprising: a first and second transmissive panel, each with an array thereon comprising rows of prismatic forms; a support framework separating said first and second transmissive panels; wherein said support framework is constructed of an injection molded plastic material.

35. A double paneled window according to claim 34 wherein said injection molded plastic material comprises reinforcing material.

36. A double paneled window according to claim 35 wherein said reinforcing material is glass fibers.

37. A double paneled window according to any of claims 34 to 36 and wherein said support framework comprises lips to which the edges of said first and second transmissive panels are sealed.

38. A double paneled window according to any of claims 34 to 36 and wherein said support framework comprises regions of enlarged dimensions, such that said regions may be used for mounting purposes.

39. A double paneled window according to any of claims 34 to 38 and wherein at least one of said first and second transmissive panels is constructed of an injection molded plastic material.

40. A double sided panel comprising: first and second side sheets; a support framework separating said first and second side sheets ; wherein said support framework is constructed of an injection molded plastic material.

41. A double paneled window according to claim 40 wherein said injection molded plastic material comprises reinforcing material.

42. A double sided panel according to claim 41 wherein said reinforcing material is glass fibers. 43. A double sided panel according to any of claims 40 to 42 and wherein said support framework comprises lips to which the edges of said first and second side sheets are sealed.

44. A double sided panel according to any of claims 40 to 42 and wherein said support framework comprises regions of enlarged dimensions, such that said regions may be used for mounting purposes.