Background Art Screens of many types have been installed to cover openings such as windows since early times. Screens have been devised to achieve various objects including shading out of the sun and preventing persons external to the building from looking into the building. While a wide range of screens have been devised, many of the designs have incorporated louvers in horizontal or vertical or both horizontal and vertical orientations. Nevertheless, such louvered designs have been of relatively simple configuration.

Recently, with the development of laws relating to privacy, regulations have been incorporated into building codes in certain jurisdictions to restrict the vision from a window. This reverses previous practices where the concern was solely to restrict people looking into a window from outside a building and instead limits the vision of a person looking out from a window. In addition there is a greater awareness and requirement for limitation of sunlight entry into a building during summertime and enhancing that light entry during winter time.

Typically, the regulations impose restrictions in both the downward and lateral directions. With regard to lateral vision, there is a restriction on the placement of windows in a new building so that an occupant cannot readily see into a window in an adjoining building. By conventional design, this regulation severely limits

the ability of a building designer to incorporate a window on a side face of a building. With regard to vision in a downward direction, there is a restriction when a window is installed above a certain height to limit the downward vision to a certain angle, typically 30°.

Disclosure of the Invention Accordingly, the invention resides in a screen adapted to restrict vision through an opening in a direction located in a plane which is at an angle greater than the angle of a viewing plane which is at a desired angle off-set from a normal axis of the screen, the screen comprising a first set of parallel louvres, spaced across the screen, said louvres being transverse to the viewing plane, each louvre having an external edge, said external edges being co-planar to define an external plane, the screen further comprising a second set of louvres which are parallel with each other, wherein louvres of the second set are alternately disposed between louvres of the first set across the screen, each louvre of one of said sets having an internal edge, said internal edges being co-planar to define an internal plane, wherein the louvres of said second set extend only partially between the external plane and the internal plane.

According to a preferred feature of the invention, the louvres of the second set are parallel with louvres of said first set.

According to a preferred feature of the invention, the internal plane is parallel to said external plane.

According to a preferred feature of the invention, the louvres are oriented transversely to the external plane., According to a preferred feature of the invention, the louvres are planar.

According to a preferred embodiment, each of the louvres of the first set are substantially equidistant from adjacent louvres of the pairs of louvres of the second set.

According to a preferred embodiment, each louvre of the second set is offset from the central axis between adjacent louvres of the first set.

According to a preferred embodiment, the screen is provided with a frame surrounding and supporting the louvres.

According to a preferred embodiment, the internal edges are disposed on the first set of louvres and each of the louvres of the second set has an external edge co-planar with the said external plane and an internal edge, said internal edges being co-planar at an intermediate plane intermediate said external and internal planes.

According to a preferred embodiment, the intermediate plane is substantially midway between the external plane and the internal plane.

According to a preferred embodiment, the internal edges are disposed on the second set of louvres wherein louvres of the first set extend a first predetermined distance between the external and internal planes and louvres of the second set extend a second predetermined distance between the external and internal planes.

According to a further aspect, the invention resides in a screen comprising a first set of parallel, upright louvres, spaced across the screen, each louvre having an external edge and an internal edge, said external edges being co-planar to define an external plane and said internal edges being co-planar to define an internal plane substantially parallel to said external plane, the screen further comprising a second set of upright, parallel louvres which are parallel with the louvres of the first set, each of the louvres of the second set having an external edge co-planar with the said external plane and an internal edge, said internal edges being co-planar at an intermediate plane intermediate said external and internal planes, said louvres of the second set being alternately disposed between louvres of the first set.

According to a preferred feature of the invention, the relative width of the second set of louvres is selected to limit the lateral vision of a person looking through the screen to a selected degree.

According to a further aspect, the invention resides in a screen comprising a first set of parallel, substantially horizontally oriented louvres, spaced across the screen, each louvre of the first set having an external edge, said external edges being co-planar to define an external plane, the screen further comprising a second set of parallel, substantially horizontally disposed louvres, each louvre of the second set having an internal edge, said internal edges being co-planar to define an internal plane wherein the internal plane is parallel to and inwardly disposed from the external plane, louvres of the second set being spaced across the screen alternately and parallel to louvres of the first set, wherein louvres of the first set extend a first predetermined distance between the external and internal planes and louvres of the second set extend a second predetermined distance between the external and internal planes.

According to a preferred feature of the invention, the relative spacing between louvres of the first set and louvres of the second set is selected to limit vision in an upward or downward direction beyond an angle from the horizontal by a person looking through the screen. According to a preferred embodiment, the vision is limited in a downward direction.

According to a preferred feature of the invention, the orientation of the louvres relative to a horizontal plane and the relative spacing between louvres of the first set and louvres of the second set are selected to limit sunlight entry to a predetermined sunlight-angle. According to a preferred embodiment, the predetermined angle is selected according to the latitude of use of the screen.

According to a preferred feature of the invention, the second predetermined distance is equal to the first pre-determined distance. According to a preferred embodiment, the first and second predetermined distances are three-quarters of the distance between the external and internal planes. According to a preferred embodiment, the first and second predetermined distances are selected to

enable the spacing between louvres of the first set and louvres of the second set to be calculated according to the equation: X = W * tan where: X is the spacing downward of the louvre of the second set from the louvre of the first set, and W is the spacing between the external plane and the internal plane, and is the angle at which visibility is completely obstructed.

According to a preferred embodiment, the first and second predetermined distances are selected so that the sunlight-angle is determined by the equation: Y = (W/2) * tan a- (W/2) * tan where: Y is the spacing downward of the louvre of the first set from the louvre of the second set, and W is the spacing between the external plane and the internal plane, and is the angle at which visibility is completely obstructed, and a is the sunlight-angle relative to the horizontal.

According to a preferred embodiment, the arrangement is configured so that the angle of orientation of the louvres from the normal to the external plane is determined by the equation: tan 9 = (tan a-2 tan 3 where : 6 is the angle of orientation of the louvres from the normal to the external plane, and (3 is the angle at which visibility is completely obstructed, and a is the sunlight-angle relative to the horizontal.

According to a preferred embodiment, the arrangement is configured so that the angle of orientation of the louvres from the normal to the external plane is determined by the equation: L = (3 * W * cos A)/4 where: L is the width of the louvre, A is the angle of orientation of the louvres from the normal to the external plane, and W is the spacing between the external plane and the internal plane.

According to a further aspect, the invention resides in laminated glass comprising a pair of glass sheets bonded into a pane by a lamination layer of plastics material wherein a screen as described above is embedded within the lamination layer.

According to a preferred embodiment, the plastics material of the lamination layer is a polycarbonate.

According to a preferred embodiment, the plastics material of the lamination layer is an epoxy resin.

The invention will be more fully understood in the light of the following description of two specific embodiments.

Brief Description of the Drawings The description is made with reference to the accompanying drawings, of which: Figure 1 is a perspective view of a screen according to the first embodiment; Figure 2 is an enlargement of a section of the screen shown in Figure 1; Figure 3 is a section view of a portion of the screen of Figure 1 taken through a horizontal section plane ;

Figure 4 is a diagrammatic sectional view through a horizontal plane through the screen as shown in Figure 1; Figure 5 is a diagrammatic representation of the visibility through a horizontal plane through the screen as shown in Figure 1; Figure 6 is a diagrammatic representation of the visibility through a horizontal plane through a screen which is an adaptation of the screen as shown in Figure 1; Figure 7 is a diagrammatic representation of the visibility through a vertical plane transverse to the window through the screen as shown in Figure 1; Figure 8 is a diagrammatic representation of the visibility and sunlight entry through a vertical plane through the screen as shown in Figure 1; and Figure 9 is a vertical cross-section through a pane of laminated glass according to the second embodiment.

Detailed Description of Preferred Embodiments As indicated previously, the invention has been devised as a result of constraints being imposed on architectural design which are intended to better accord occupants of adjoining houses privacy from their neighbours. Constraints are imposed both on the lateral vision through an opening and also in the direction vertically downwards. With regard to lateral vision, the"R CODE" (the Residential Design Code) of Western Australia restrict a window being positioned in a wall of a domestic building whereby an occupant can look into a window of an adjacent house. The R Codes contemplate that the constraints imposed may be achieved by the provision of a screen. It is proposed that the object of the constraints can be achieved by providing a novel screen which limits the view of the occupant appropriately yet provides sufficient direct vision and sunlight entry into the house. The code also limits downward vision when a window is above a certain height to a maximum of 30 degrees below the horizontal.

In describing the constraints, the R Codes defines a"Cone of Vision", being a means of defining a range of vision by a viewer situated 500mm behind a window. The limits of the Cone of Vision can be seen to be defined if the visibility is reduced below 20% of normal visibility. This definition is used within the specification to help describe the invention and its benefits, but it should be realized that any reference to a Cone of Vision should not be considered as limiting the scope of the invention.

As well as a restriction on lateral vision, it is desirable to provide a screen which limits direct sunlight entry according to a design angle determined from the latitude of the site. With an appropriately selected angle the screen will block out midday sun during summer but allow midday sunlight to enter the premises during winter.

The embodiment of the invention is directed to a screen adapted to provide restricted vision in accordance with certain predefined constraints and also to limit the entry of summertime sun into the building through the window. For convenience, the embodiment will be described with reference to a building situated in a latitude south of the Tropic of Capricorn whereby summertime sunlight is maximum on a northwards facing window. It should be recognised that when the invention is applicable to a building situated north of the Tropic of Cancer, the summertime sunlight is maximum on a northwards facing window and therefore the references to north and south made in the description should be reversed. While generally a building situated in between the equator and the Tropic of Capricorn will follow the criteria as described in relation to a building situated south of the Tropic of Capricorn, certain additional considerations need to be taken when applying the invention. Similar consideration will also apply if the latitude is between the Equator and the Tropic of Cancer.

The first embodiment of the invention is directed to a screen adapted to be installed adjacent to the external surface of a building window. As shown in Figures 1a and 1b, the screen 11 of the embodiment comprises a generally rectangular frame work 21 supporting a plurality of vertically oriented louvers 22

and horizontally oriented louvers 23 between an external face 25 and an internal face 26. The embodiment is particularly adapted for use in an opening facing the north.

The vertical louvres 22 act to restrict vision through the screen in a direction located in a vertical plane which is at an angle greater than the angle of a vertical viewing plane which is at the required angle off-set from the normal axis of the screen. The vertical louvres 22 are adapted to restrict lateral vision of an observer within the building while optimising sunlight entry within the constraints imposed by the required restriction on lateral vision. The operation of the vertical louvres is described with reference to Figures 2 and 3 but it should be noted that, for clarity, within these drawings, details of the horizontal louvres are not shown.

The vertical louvres 22 are planar and parallel and extend normally to the internal and external faces of the screen. To achieve the previously mentioned object, the screen comprises two types of vertical louvres 22 disposed alternately across the screen. The first type of vertical louvres 22 is a full vertical louvre 31 of full depth extending substantially transversely from the external face 25 of the screen to the internal face 26. The second type of vertical louvre 22 is a reduced depth louvre 32 extending transversely from the external face 25 to a depth substantially mid-way between the external face and the internal face.

The configuration is better appreciated by reference to Figure 4. In this diagrammatic view, it can be seen that the arrangement defines a diagonal line 34 extending from the point of intersection of a first full louvre 37 with the external face 25 to a point of intersection of an adjacent second full louvre 38 with the internal face 26. A corresponding diagonal line 35 is also defined between the point of intersection of the adjacent second full louvre 39 with the external face 25 to a point of intersection of the first full louvre 40 with the internal face 26. It can be seen that the inner edge of the reduced depth type of louvre 32 is approximately located at the intersection of these diagonals. By this configuration, the geometrical configuration of the arrangement can be specified by reference to the angle of the diagonals 34 and 35 to the plane of the external

(or internal) face, only (angle 0). According to the arrangement, the relative visibility and sunlight admitted through the screen does not vary with the depth of the screen provided the geometry indicated is maintained.

The lateral visibility through the screen of the first embodiment is illustrated in Figure 5. The visibility is taken at the point 51,500mm behind the window, as required by the Code. The screen is configured to provide a Cone of Vision of 90 degrees. The shaded bands 52 represent the segments of lateral visibility which are obscured by the vertical louvres 22, while the unshaded bands 53 represent the unobstructed regions. It can be seen that visibility in a direction transverse to the window is almost unobstructed, the main obstruction being the thickness of the louvres 22. However, as the angle of vision from the normal increases, a greater percentage of the viewing path is obstructed by the louvres. At the angle of 45 degrees from the normal, the vision is restricted to 20% of full vision which is designated in the Code as an accepted cut-off value.

As a result of the arrangement, the vertical Cone of Vision can be limited to a defined angle by selecting an appropriate angle 6 of the diagonals 34 and 35.

The benefit of the arrangement is that the limitation on viewing is achieved while allowing greater entry of sunlight to the window during the day.

The advantage is illustrated by another example. As shown in Figure 6, in order to provide a Cone of Vision of 60 degrees, the angle of the diagonals is required to be approximately 42 degrees. At this angle, sun incident on a northward facing screen, will contact the glazing of a North facing window directly between the hours of just before 9: 00 am until just after 3: 00 pm at the Equinoxes. While it is possible to achieve an equivalent Cone of Vision with a screen comprising vertical louvres all of the same depth, it would be necessary to separate with an angle of diagonals of approximately 52 degrees. In this case the period of the day during which the sunlight would directly incident the glazing would be considerably reduced. In addition, particularly at the greater angles of incidence, the proportion of sunlight incident upon the glazing would also be reduced. For example for the conditions above, at a solar angle of 60 degrees, the proportion

of sunlight incident on the glass is about 20% for the screen with equal depth louvres while it is about 25% for the present embodiment.

For the arrangement, as shown in Figure 5, the angle of the diagonals 34 and 35 is reduced. This arrangement widens the relative spacing between the louvres for a fixed depth of screen. As a result sunlight would contact the glazing of a northward facing window for a considerably greater period of the day, although the viewing angle would be increased. In this example, a diagonal angle of 34 degrees, provides the viewing angle of about 90 degrees while the sunlight time is extended.

It can thus be seen that the performance of the screen can be varied by altering particular features of the design of the screen. As well as changing the relative angles as described above, the performance of the screen may be adapted by altering various other features. For instance, by biasing the position of the reduced depth louvres 32 slightly from a central position between the adjacent full depth vertical louvres 31, it is possible to increase the proportion of sunlight received during one of the morning or afternoon periods at the expense of the other. Alternatively, it is possible to orient the louvres at an angle away from the normal from the external and internal faces which may be preferred for windows that are not northward facing. Also, it may be preferred in certain instances to orient the louvres somewhat away from the vertical.

The screen 11 is also designed to restrict vertical vision below horizontal to a predetermined angle as specified in relevant building regulations. The horizontal louvres 23 act to restrict vision through the screen in a direction located in a plane which is at an angle greater than the angle of a viewing plane which is at desired angle off-set from a normal axis of the screen. Typically the angle specified is 30° and henceforth the angle of 30° will be used in reference to this specified angle. However a different angle may be used instead in the embodiments if appropriate.

To prevent an observation angle downwards of greater than 30° and to restrict sunlight entry in the required manner, the screen provides an array of parallel

horizontal louvers extending for a width of three-quarters of the distance between the external face and the internal face of the screen with alternative louvers set from the rear face and the front face sequentially. By selecting precisely the angles of the blades and the distance apart of the blades it is possible to provide precisely the required cut off angles.

The geometry of the arrangement is explained in more detail with reference to Figure 7. The horizontal louvres 23 are planar and parallel and comprise external louvres 61 extending from the external face 25 and internal louvres 62 extending from the internal face 26 alternately. The internal and external louvres are set alternatively across the height of the screen. The louvres are set at an angle 0 and arranged to extend three-quarters of the distance between the external and internal plane.

The external louvre 61 is positioned a particular distance X below the internal louvre 62 to prevent vision downward beyond a first predetermined angle from the horizontal from the internal side. The necessary displacement X of the external louvre 61 relative to the internal louvre 62 can be calculated relative to the distance W between the external plane and the internal plane by the equation: X = W * tan (3 where: (3 is the angle at which visibility is completely obstructed.

The internal louvre 62 is positioned a particular distance Y below the external louvre 61 to prevent sunlight entry when the sun is above a selected sunlight angle P from the horizontal on the external side. The necessary displacement Y of the internal louvre 62 relative to the external louvre 61 can be calculated relative to the distance W between the external plane and the internal plane by the equation: Y = (W/2) * tan a- (W/2) * tan

where: ß is the angle at which visibility is completely obstructed, and a is the sunlight-angle relative to the horizontal.

It is anticipated that the sunlight angle will be selected midway between the maximum summer sun angle and the minimum winter sun angle, although this compromise may be varied.

To construct the screen, the orientation 6 of the louvres relative to the normal of the external (or internal) plane can be calculated according to the equation: tan 9 = (tan a-2 tan (3)/3 where: 6 is the angle of orientation of the louvres from the normal to the external plane, and ß is the angle at which visibility is completely obstructed, and a is the sunlight-angle relative to the horizontal.

Finally, the width of the louvres can be calculated according to the equation: L = (3 * W * cos 6)/4 where : L is the width of the louvre, A is the angle of orientation of the louvres from the normal to the external plane, and W is the spacing between the external plane and the internal plane.

The performance of the screen is illustrated diagrammatically in Figure 8, which shows the visibility through the screen below the horizontal and the sunlight entry above the horizontal. The shaded areas indicate the regions obstructed by the louvres in each case.

It should be noted that at angle ß vision is completely obstructed. The Code only requires visibility to be reduced to 20% and therefore a greater cut-off angle can be determined which will fall within the Code.

As can be seen from the above description, the first embodiment enables the vertical vision and sunlight entry to be controlled according to the various constraints imposed. It will be recognized that, while the particular embodiment leads to an arrangement whereby the various parameters of the screen are easily calculated, alternative arrangements of a screen may be devised in accordance with the invention which limit the vision and sunlight entry but have parameters differing from those of the embodiment. For instance, arrangements can be determined whereby the louvres extend for other than three-quarters of the distance between the external and internal louvres.

While the embodiment described is directed to a northward facing window, it is to be appreciated that screens incorporating at least some of the features may be devised which will be applicable to other orientations. For example, for a southward facing window, there is no need to seek to provide any restriction on sun-entry. Nevertheless, control of lateral and downward vision remains important. For windows close to the ground, there is no need to provide downward control. Thus a range of screens falling within the scope of the invention can be devised to suit a specific requirement.

While the first embodiment has been described as being external to the window it may easily be adapted to be installed internally or indeed, in the case of a double glazed window may be installed within the spacing between the two panes of glass. This last installation would avoid the need for routine cleaning of the screen.

The concept of placing the screen between two panes of glass leads to a further development. It has now become possible to produce a type of laminated glass comprising two sheets of glass and an intermediate lamination layer of transparent plastics material such as polycarbonate or epoxy resin in which a form is embedded. This development allows a screen having the features

described in the first embodiment to be embedded in the lamination layer. An embodiment of such an arrangement is shown in Figure 9. It will be seen that the laminated glass 90 of the embodiment comprises inner glass sheet 91 and outer glass sheet 92 with a first set of louvres 93 extending from proximate the inner glass sheet 91 within the laminated layer 93 and a second set of louvres 95 extending from proximate the outer glass sheet 92 within the laminated layer 93.

In the embodiment, the louvres shown are horizontal louvres configured in the same manner as for those as shown in Figure 7. It will be appreciated that the pane may also include a set of vertical louvres While the screen provided by such an arrangement will be very thin compared with conventional screens and therefore require a considerably larger number of louvres for a particular height or width of screen, this disadvantage is offset because the louvres can be manufactured from very thin material such as metal foil or film. While this process is still in development, it is believed that the ratio of louvre spacing to louvre thickness can be comparable if not even better than for conventional screens so that the optical performance will also be comparable or better. Such an arrangement has many potential advantages. As the louvres are permanently embedded in the lamination layer, there is no risk of damage, other than the normal risk of glass breakage. Installation is as for any other pane of glass. The louvres are fully protected from oxidation and so will not discolour. Also, the need for any screen other than the window is removed-a saving in cost and improved aesthetic appearance.

Modifications and variations as would be known to the skilled addressee are considered to be within the scope of this invention and it should be appreciated that the present invention need not be limited to the particular scope of the embodiment described above. It will also be appreciated that throughout this specification the terms vertical and horizontal when used in relation to louvres are intended to designate the usual, relative orientation of the various sets of louvres in a common configuration. It will be appreciated in certain configurations the"vertical"and"horizontal"may not be perpendicular in orientation and be installed so that neither sets are oriented truly vertically or

horizontally. This terminology is not to be taken to restrict the generality of the description.

Throughout the specification, unless the context requires otherwise, the word "comprise"or variations such as"comprises"or"comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.