GB2154268A

GB2154268A - Window blinds

Info

Publication number: GB2154268A
Application number: GB08419777A
Authority: GB
Inventors: Howard Ivan Gardner
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-02-06
Filing date: 1984-08-02
Publication date: 1985-09-04
Also published as: GB8419777D0; GB8403092D0

Abstract

A shade for a window comprises at least two sheets of relatively movable partially transparent material, such as polarizing material. In the embodiment shown, two overlapping sheets of polarizing material have alternating regions with different planes of polarization. The regions are outlined by lines 2 and arrows 1 show the direction of polarization. The sheets are shown in the transmission mode. As the sheets are moved relatively in the direction of arrow 3 the directions of polarization on the adjacent sheets will cross, rendering the combination opaque. Also disclosed is the use of an electro-optic system, such as liquid crystals, for providing shading. <IMAGE>

Description

SPECIFICATION Polarshade The present invention relates to shading windows and, in particular, aims to provide an alternative to blinds or curtains. The invention may also be applicable to other systems where shading, particularly variable shading, is required, e.g. sunglasses and visors.

A first aspect of the invention provides a shade for a window or the like, comprising at least two sheets of relatively movable material. One of the sheets may form the window itself.

According to a preferred feature of the invention, both sheets consist of a polarising material. Each sheet comprisea a plurality of areas having different directions of polarisation. The areas may be formed into a repeating pattern in a preferred direction of relative movement of the sheets. Preferably the pattern of areas is such that at certain different relative portions of the sheets the difference in the angle of polarisation for overlapping areas of the sheets is different and substantially constant across the sheets. It is envisaged that a continuously varying angle of polarisation may be provided along the sheets, for example varying sinusoidally.

According to another preferred feature of the invention, provision is made for the use of non-polarising materials comprising specifically patterned or textured sheets. The relative movement of overlapping sheets generates variable interference patterns which in turn are designed to provide variable light transmission through the sheets. An example of a suitable pattern for each sheet consists of small regularly spaced and uniformally sized squares which are alternately opaque and transparent.

The first aspect of the invention will be further described hereinafter under the heading polarshade.

A second aspect of the invention provides a shading system comprising a layer of an electro-optic material.

The term electro-optic material refers to materials or substances in which the light transmission properties of the material or substance can be varied by applying an electric field or voltage across the material.

Examples of such materials are liquid crystals. By applying an electric field across certain types of liquid crystal the amount of light transmitted by the crystal may be varied. An example is the dynamic scattering effect of nematic liquid crystal, which may be transparent in the absence of an applied field and become milky white on the application of a small voltage across the crystal.

Other examples of such materials include substances which change or rotate the plane of polarisation of light passing through the material. An example is twisted nematic liquid crystal. The liquid crystal is arranged between two polarising filters at an angle to one another so that, in the absence of an applied field, polarised light is transmitted through a first of the filters and then rotated by the nematic liquid crystal sufficiently to pass through the second filter. By applying a small voltage, such as an alternating voltage of a few volts, across the liquid crystal, the rotational power of the crystal is lost so that polarised light will not pass through the crossed polarising filters. Other examples of such material are substances which exhibit the Kerr electro-optic effect.Such substances are normally isotropic but become anisotropic on the application of a mechanical stress, or a strong static magnetic or electric field. The result of this anisotropy is that the plane of polarisation of polarised light passing through the material will be altered. Hence by using such material in conjunction with suitably aligned polarising filters the transmission of light may be controlled by a voltage applied across the material.

Where the electro-optic material itself may act as a polariser, a single polarising filter may be used to provide shading.

Very preferably, the electro-optic material and/or the associated electrodes are arranged in areas or bands, to give a banding effect on the window to be shaded. Hence, as will be described hereinafter, the degree of shading across or down a window may be varied, to give an effect similar to the shading given by a roller blind or a venetian blind.

Preferably, controls are provided to enable the areas of electro-optic medium to be controlled individually or in groups. Also the field applied to an area may be variable in a controlled manner to allow variable control of the amount of light transmitted by the medium.

Transparent electrodes may be used for applying a voltage across the electro-optic medium, in a manner similar to that used in liquid crystal displays.

'POLARSHADE'-WHAT IT IS AND HOW IT WORKS 'POLARSHADE' is a completely new way of shading or screening windows from unwanted light both natual and artificial. The design of one form is based on the scientific phenomenon of light polarisation. In simple terms, when light passes through polarising material perpendicularly the light which is transmitted consists of vibrations which are limited to one direction in the plane perpendicular to the light source. This emerging light is said to be plane polarised. If this plane polarised light is then made to pass through a second piece of polarising material it will be noted that unless the plane of polarisation in the second piece is the same as the first there will be a partial to almost total restriction on light transmission through the second piece of polarising material.The degree of light penetration through the second piece depends on the angle between the plane of polarisation in the first and second piece of polarising material. Therefore if the two planes of polarisation are parallel there will be a minimal loss of light transmission, thus the light intensity emerging from the second piece of material will be only marginally lower than the intensity of the source (see below 'POLARSHADE EO'). At the other extreme, if the two planes of polarisation form a right angle (90 ) then almost none of the plane polarised light from the first will be able to pass through the second piece of polarising material. At intermediate axial angles, as. mentioned above, there will only be a partial obstruction of light and this depends on the particular angle made by the two planes of polarisation.

The polarising form of 'POLARSHADE' consists of two pieces of a specially prepared polarising material. One sheet is fixed to the window or glass pane to be shaded whilst the other sheet rests, for instance, in grooves so that it can be made to slide over the fixed sheet of material. The polarising material is constructed in such a way that only a very small sliding movement (perhaps 2 cm) will be necessary to effect a maximum reduction in light transmission through the inner sliding sheet. This sliding movement may be achieved manually e.g. by simply pulling a lever or handle or mechanically by incorporating a small electric motor to do this job.

The material used in both sheets contains several 'panels' of a polarising material. In each panel there is a different plane of polarisation {se,e.. Fig.1 )A.:S anample the ,irst panel will have a vertical pl,a. of- polarisation, the .ecO;.fldQA 5:':;-lE -.diaonal plane th..- third a horizontal plane and the fourth, say a a 45-'; N-W.. of plpe,.of polarisation After. this the subsequent panels merely repeat the pattern across the length of the sheets.

The sliding sheet will be one or more panels longer than the fixed sheet so that the window is covered by this sheet when it is moved across the fixed sheet. When the pattern of the panels of polarisation of the fixed and sliding panels matches there will be virtually no loss of light transmission and the occupants of the room will have an almost unrestricted view of the outside (but see below).

When the sliding sheet is moved the width of one panel in the appropriate direction then, as in Fig. 1. the sliding sheet is moved one panel in width to the left, all the diagonal planes (i.e. 45 N.E. and 45 N.W.) of the movable sheet will rest over all the vertical planes and the horizontal planes of polarisation respectively of the fixed sheet, and all the vertical and horizontal planes on the movable sheet will rest over all the diagonal planes respectively in the fixed sheet. The result here will be a partial shading of the room.When the sliding sheet is again moved another panel's width in the appropriate direction, then, if as in Fig. 1. the sliding sheet is moved a second panel width to the left, all the vertical and horizontal planes of the sliding sheet will rest over all the horizontal and vertical planes of polarisation of the fixed sheet. So the angle made between these planes will be 90 . Likewise all the 45 N.E.

diagonal planes and all the 45 N.W. diagonal planes in the top sheet will rest over each oppositely directed diagonal plane of polarisation in the fixed sheet. Once again the resulting axial directions made by overlapping both sheets in this way form a right angle. In all cases where the angles made between the two planes of polarisation form 90 there will be hardly any light passing into the room.

The above example merely shows the straight forward and basic operation of 'PO LARSHADE' Fig. 1. shows a four panel pattern which permits three main possible degrees of shading: 1) An almost clear view to the outside with zero or very little light obstruction apart from some unavoidable minor loss of light transmission referred to below in 'POLARSHADE EO'.

2) A partial shade, which on the above angles, would result in a welcomed moderation of excessive sunlight (i.e. a reduction in light intensity). Such a partial shading does not obscure the occupants' view to the outside completely since the transparency of the glass is only partially reduced.

3) In its third and, in this example, final position there is a very significant reduction in the amount of light entering the room. From .;the view Iothe-outside- only the sun or very bright artificial larnps-are visible and these take on a pleasant deep blue colouring.

Otherwise - when there is-n-o direct sunlight or other direct bright light sources the window looks blue/black in colour and-inthiscase:-.- 'POLARSHADE' serves as a very effective blind. In its third position (and to some extent also in its second position) the view from the outside of the window looking in is almost completely obstructed so that in this case 'POLARSHADE' functions as curtains or blinds.

N.B. although the example of the panel pattern in Fig. 1. describes the three main possible degrees of shading, it is in fact also possible to obtain intermediate degrees of shading. This is achieved by simply moving the sliding sheet in such a way that only part of each panel of this sheet rests over the panels of the fixed sheet. It will be noted that in any of these intermediate positions what I have termed as a 'banding' effect will occur i.e. th window will show bands of varying degrees of shading.

With a greater number of panels per panel pattern or a different polarising pattern (see Fig. 2.) it is possible to have a wider range in degrees of shading with more gradual changes between the two extremes. However, in these more complex patterns 'banding' may occur (though not necessarily-see Fig. 2.) even when fixed and sliding panels rest directly above one another.

In the case of round panes of glass such as portholes 'POLARSHADE' can be applied with even greater ease. This system merely involves having the movable plane polarised surface pivoted at its centre and simply by revolving this about its centre, the various angles can be created between the two planes of polarisation with the result of achieving the desired amount of shading or screening.

As an alternative to polarising materials, it is possible to use interference patterns generated between two or more relatively movable sheets of a suitably designed non-polarising material so that, as with polarisers, varying degrees of light transmittance will be achieved by small relative movements of these sheets.

For example, the pattern on each sheet may take the form of a series of regularly spaced spots, squares or lines of light reflecting or aborbing coatings on essentially transparent glazing materials or through the use of specially textured glazing materials made, for example, by an etching or engraving process.

The interference pattern may have a different transmittance/reflectance characteristic when viewed internally or externally i.e. good visibility may be achieved when viewing out through the pattern whilst sunlight would be highly reflected.

'POLARSHADE EO' The basic idea behind 'POLARSHADE' can be further developed by incorporating in the system an electro-optical device (hence 'EO').

In essence exactly the same processes which provide the light obstructing effect in a previously described form of shading will be seen to be working in 'POLARSHADE EO' namely that light polarised in a plane which is 90 to the plane of polarisation of another polariser will not pass through this second piece of material. However, the main difference in 'PO LARSHADE EO' is that the plane polarised light which passes through the first polariser is electro-optically varied or modulated so that by the time it passes out of the electro-optic medium the plane polarised light will have been modulated in a particular way. This is because when the electro-optic device is operated the polarising properties of the substance within the device (solid or liquid) are altered.

This is attributable to the 'Pockels' or 'Kerr' effect. With some types of electro-optic materials the plane polarised light entering the medium becomes eliptically polarised the shape of the elipse varying with the applied voltage. Loosely speaking one can say that the light passing out of the electro-optic device is retarded inasmuch as its plane of polarisation is no longer the same as the plane polarised light which enters the device. However, since the electro-optic modulator is not a polariser the light will pass through it-it being transparent irrespective of the applied voltage.If another polariser, whose plane of polarisation is parallel to the input polariser, is placed across the output side of the device then the modulated plane polarised light should be 'totally' (apart from any light leakage due to the particular polarising materials used) or partially obstructed by the second polariser.

Whether or not the light is 'totally' or partially obstructed will depend inter alia upon the voltage which is applied through the electrooptic medium.

The success of the operation of this system will depend on: I) The type and possibly the size of the electro-optic medium chosen. For example a large number of long and narrow electro-optic devices may in practice be required to cover the glass to be shaded.

II) The positioning of the two polarisers in relation to each'other as well as to the direction of the applied voltage through the electrooptic medium.

III) The amount and variability of the voltage applied through the electro-optic medium.

IV) Possibly the temperature of the electrooptic medium.

What does 'POLARSHADE EO' offer to the user? In its intended form the electro-optic version of 'POLARSHADE' will be used to shade domestic, commercial, and horticultural glazing electronically at the touch of a button. Since there will be no moving parts in the system the possibility of mechanical failure will be completely excluded. In addition, by varying the voltage passing through the system the degree of shading can be altered as desired.

This variation of the applied voltage would possibly be achieved (though perhaps indirectly) by using a kind of dimmer switch currently used in lighting systems. When the switch is off, no electro-optic effect will occur, and so since the two polarisers rest opposite each other and have the same plane of polarisation the light entering through the pane of glass will pass straight through both polarisers and the transparent electro-optic medium in the middle) see Fig. 3.). In this case there will be no shading apart from: 1) Any unavoidable but minor loss of light transmission attributable to the polarising materials used-that is polarisers do tend to absorb a proportion of the incident light.

2) Any small loss of light which is reflected back from the polarising surfaces. In practice, if this should prove to be undesirable, a way of reducing this loss would be to use antireflection coatings on the materials.

3) Any small loss of light transmission due to the effect which may take place between the plane polarisers and the partial polarisation of skylight. (This partial polarisation of skylight may produce a mild banding or blotched effect in non-electro-optic 'POLAR SHADE' systems even when the matching fixed and moving panels or polarising patterns overlap. This is very much a weather-dependent phenomenon. On clear days when the sky is deep blue the effect may be fairly pronounced. When the sky is grey the effect will be negligible. The application of a light scattering/de-polarising coating to the outward facing side of the first polariser (fixed sheets in my examples) or a separate sheet of such a material placed in front of the first polariser will markedly reduce the the effects of any skylight polarisation but at the same time previously clear glass may take on a hazy appearance.

When the switch is turned so that it permits, for example, half the optimum applied voltage to pass through the electro-optic medium then this will partially shade the glass.

Finally, when the switch is turned to allow the maximum necessary electro-optic effect to occur the greatest possible degree of shading will be apparent.

Another type of electro-optic medium which may be used in 'POLARSHADE EO' is the socalled 'twisted nematic' liquid crystal. This works by turning the direction of any plane polarised light passing through it through 90 automatically, that is, without any applied voltage. If a second polariser is placed on the output side of the crystal then, providing its plane of polarisation is at right angles with the ptane of pólarisation of the first polariser, light wilf pass throúgh the whole arrangement unobstructed. When an applied voltage is passed through the electro-optic medium the plane pofarised light from the first polariser passes straight through the medium without any effect on the plane of polarisation.Since the plane of polarisation of the second polariser is at right angles to that of the first most of the light which passes out of the crystal will be blocked by the second polariser. With this type of electro-optic device intermeidate degrees of shading are achieved by passing the required voltage through the device with very quick on and off pulses. The degree of shading will depend on the length of the voltage pulse.

The flexibility of 'POLARSHADE' in all of its forms including the electro-optic variant is such that it is possible to accommodate double glazing within the systems described. Indeed the polarisers themselves may be used for this purpose if made of a suitable material for example, glass laminated polarisers-see Fig. 4. Furthermore the use of these shading systems on windows will by no means necessarily prevent the windows from being opened and closed. For instance it will be no problem to attach the fixed and movable sheet polarisers (or, in the case of 'POLARSHADE EO', the fixed polarisers and the electro-optic device) to the window in such a way that the whole unit, whether double glazed or not, will be free to open and close on pivots, hinges or by sliding in grooves.

Needless to say, it will quickly become apparent that the systems which I have described are capable of further modification or variation but for the time being and in the interest of presenting a relatively concise account, I have restricted myself to the basic operations referred to above.

Other types of electro-optic devices, such as ordinary liquid crystals, not necessarily requiring the use of an associated polarising filter or filters may be used in a manner similar to the 'POLARSHADE EO' systems. Like the twisted nematic types, these "ordinary" liquid crystals are transparent when there is no applied voltage but become milky white on applying a voltage. due to an increase in scattering power. A variation of the applied voltage may allow for a controlled variation of the amount of light transmitted.

When reference is made to a variation of applied voltage and to an increase or decrease in applied voltage, this may be taken to include variations in the frequency of an applied alternating voltage, a combination of opposing alternating voltages, variation in the rate of application of voltage pulses and other changes in the characteristics or directions of the applied voltage(s) or electric field(s).

N.B. 'glass', 'glass pane', 'window', and 'glazing' should also be taken to include materials other than purely siliceous substances for example plastics.

The electro-optic shading systems are particularly adaptable to provide shading similar to that in known systems such as roller-blinds and venetian blinds. Such systems will be described hereinafter by way of example with reference to the 'POLARSHADE EO' system incorporating polarising filters, however the banding and other arrangements shown are also applicable to the systems, such as the liquid crystal systems, which do not require an associated polarising filter or filters.

ELECTRO-OPTIC FORMS OF EXISTING SHADING SYSTEMS It has been shown that 'POLARSHADE EO' represents a new way of reducing the amount of light passing through glazing materials. The system differs from existing forms of shading in two main respects: 1. It is a purely non-mechanical device so that the only part of the system which moves is the electronic switch.

2. The shading effect takes place in such a way that the whole of the window becomes darker at the same time and therefore for any given applied voltage the window will provide a uniform amount of shade.

In practice it may well be desirable to maintain some of the particular shading characteristics of existing shading systems. Here it is my intention to briefly describe how 'PO LARSHADE EO' can be made to retain some of these characteristics.

ELECTRO-OPTIC ROLLER BLINDS In order to achieve a roller blind-type mode of operation the electro-optic medium between the two polarisers will be composed of several narrow cells (strips). These will span the window horizontally with each one resting directly below another. The electronics of the system will be such that as a variable switch is operated an applied voltage will pass through the strips starting from the top of the window and working downwards through the strips see Fig. 5. The variable switch may well take the form of a dimmer-type switch, sliding control, touch button electronic tuning-type control or the type of switch used in electric window systems in cars.

In this way the electronic 'roller blind' can be raised or lowered to the desired level. So, for instance, if the switch is operated in a way which activates half of the electro-optic strips (i.e. the top half of the window) then this top half of the window will become opaque whilst the bottom half will remain clear.

NOTE: 1. Although I have described a system which starts shading from the top of the window downwards, it will also be possible to incorporate a separate switch which can reverse this order so that, if desired, the window can be shaded starting from the bottom and working up the window as the control switch is varied.

2. It will also be possible to build into the system another independent control which is capable of varying the applied voltage passing through the electro-optic strips. This will enable the particular degree of shading given by the energised strips to be varied as desired.

VENETIAN BLIND AND VERTICAL LOUVRE TYPE ELECTRO-OPTIC SHADING SYSTEMS In order to re-create the appearance and, to a certain extent, the functional capabilities of Venetian blinds and vertical louvre blinds using electro-optical devices the electro-optic medium between the two polarisers will again be composed of several narrow strips. With the Venetian blind-type these electro-optic strips span the window horizontally and with the vertical louvre blind-type these span the window vertically. From this point the only significant difference between these systems and the electro-optic roller blind-type system is the electronic circuitry.

With the Venetian blind-type systems the height of the blind is raised and lowered in much the same way as described in the roller blind systems. However, when the height adjusting cord of conventional Venetian blinds is operated there is a gap between each of the plastic shutters and these are positioned at right angles to the window so that very little shading is afforded. It is only when the second cord is operated that the angle of the shutters is altered in order to obtain the desired degree of shading. For a suitable electro-optic Venetian blind system it will therefore be desirable to represent the operations of both the cords of a conventional Venetian blind system, that is, the height of the blind and the angle made between the individual shutters and the window. These two operations may be re-created in an electro-optic shading system in a variety of ways.

As an example only, as regards the raising and lowering of the height of the blind a similar method to that described in the electro-optic roller blind system will be used. The difference here will be that only some of the electro-optic strips will darken as the blind is lowered. To explain this let it be assumed for example that the width of each electro-optical Venetian blind shutter is 4 cm and that each one of these is made up of several electrooptic strips for example, 20 such strips each one being 2 mm wide (see Fig. 6).

In order to set the blind to the desired height a variable control is operated so that an applied voltage only passes through the top electro-optic strip of each 4 cm wide shutter (group of 20 electro-optic devices) starting from the shutter at the top of the window working down through successive shutters as the control is varied (although a separate switch may be incorporated to reverse this if desired so that these lines start at the bottom of the window and work upwards). If the blind is lowered, for example, half way down the window in this way it will be seen that the bottom half of the window remains completely clear but the top half of the window will have shown on it several narrow dark lines and that each of these lines is separated by clear gaps each one being 4 cm wide. The lowest of these thin lines (height strips) indicates the particular height of the blind chosen.Another control will serve to operate the remaining 19 (in this example) electro-optic strips in between the visible height strips. Therefore this control enables the clear gaps to be filled in.

The particular way in which these gaps are filled in may be, for example, from the top of each of the thin height electro-optic strips downwards as the control is varied. Therefore, if for instance one intends to operate the electro-optic shutters over the whole of the window with the shutters only half closed then firstly all of the height strips will receive an applied voltage and secondly the shade operating control will be adjusted so that only the top half of each of the 4 cm groups of strips (i.e. the top 10 strips of each shutter in this example) will provide shade and the bottom half of these will remain clear.

As a further refinement to this system a third switch may be incorporated-its purpose being to adjust the applied voltage passing through all of the electro-optic strips thus enabling the degree of shading afforded by the shutters themselves to be varied.

With vertical louvre-type electro-optic blinds the system will take a very similar form to the Venetian blind system as described above.

However, the main difference is that the whole electro-optic arrangement will be rotated through 90 so that, as previously mentioned, the electro-optic strips will span the window vertically instead of horizontally.

THE ELECTRO-OPTIC EQUIVALENT OF CUR TAINS A simple adaptation of the electro-optic roller blind type shading system enables a curtain effect to be achieved. This involves: 1. Rotating the electro-optic arrangement through 90 so that the strips span the window vertically.

2. For a double curtain effect (i.e. two pieces of 'curtain' which close at, say, the middle of the window) the electronics of the system will be such that when a switch is operated the electro-optic strips receive an applied voltage which starts at both the left and right hand side of the window and which works towards the middle of the window as the control is varied.

Ideally, the user will also be able to operate each of these 2 (in this example) 'curtains' independently if he/she so wishes.

Finally it may also be desirable to incorporate another switch to vary the applied voltage and hence the degree of shading provided by each of the electro-optic strips.

FURTHER NOTES The Venetian blind and roller blind type electro-optical shading systems described above differ only in the pattern in which the electro-optic strips receive the applied voltage.

Apart from these switching order differences both systems are the same inasmuch as the electro-optic strips span the window horizontally. This being the case it is possible to have the electronic switching circuitary of both systems combined and housed within one unit to form a single system which is capable of both modes of operation.

Similarly the vertical louvre and curtain-type electro-optic shading systems described above differ only in the pattern in which the electrooptic strips receive the applied voltage. Once again, apart from this, these two systems are the same inasmuch as the electro-optic strips span the window vertically. This being the case it will also be possible to combine both of these two systems to form a single system which is capable of functioning in these two modes of operation.

Finally if the vertically and horizontally stripped electro-optical units are placed together between the two polarisers then, provided that the correct choice and positioning of the electro-optic devices is used, it will be possible to enjoy the benefits of all of the four systems described in a single shading system.

POSSIBLE MODIFICATIONS TO THE ELEC TRO-OPTIC VENETIAN BLIND SYSTEM A possible improvement on the electro-optic Venetian blind shading system described above works by arranging the electro-optic shutters in tiers so as to create small gaps between the planes in which each shutter lies or each of the shutters may be positioned one above the other at a particular angle to the window with equal gaps between these shutters (see Fig. 7). Since the width of each of the gaps is perpendicular to the plane of the window the whole face of the window will still be covered by the shutters with no apparent gaps from the view outside looking in. However, it will now be possible for the occupants of the room to look down through the clear gaps to the outside.In this way it will be possible: a) to prevent direct sunlight from entering the room whilst at the same time permitting some useful daylight to pass up through the gaps and into the room.

b) the occupants of the room will have a partial view down through the gaps to the outside whilst maintaining their own privacy.

If one of these shutter tiers is capable of operating over the whole window in the way described in the original electro-optic Venetion blind shading system then the advantages of both designs can be enjoyed within a single system.

In another embodiment two layers of electro-optic shutters are provided with a gap (perpendicular to the window) between these layers. The shutters all face the window i.e.

they are not angled (see Fig. 8). These shutters alternate in such a way that from a head on view from the outside looking in the window is completely screened when all the shutters are on. However, because of this arrangement (the gaps between the two layers of alternating shutters) some daylight will pass up through these gaps and into the room whilst at the same time the room will be shaded from direct sunlight.

As a control is varied the shutters come on by alternating between layers down the window.

Note: If one of these layers (perhaps the layer furthest from the window) consists of electro-optic strips all the way down the win dow, then, given the appropriate switching circuitry and controls, this layer may also be operated as electro-optic roller blinds and/or Venetian blinds with all of the height and shading functions previously described in these systems.

A brief description of some of the drawings will now be given.

FIG 2.

This shows two other different polarising patterns.

1. This shows the directions of the planes of polarisation.

2. These lines show the divisions between the panels.

3. The arrows show the direction of movement of the sliding sheets.

FIG 3.

THE ELECTRO-OPTIC VERSION-A CROSS SECTION 1. Window-glass/plastic pane.

2. First piece of polarising material with lines showing the plane of polarisation. This plane of polarisation will be set in relation to the direction of the applied voltage through 3.

3. This is the electro-optic device. Here it is in its off position, that is, there is no applied voltage. Since there is no applied voltage there will be no electro-optic effect on the plane polarised light which passes out of 2 and into 3.

4. This shows the second piece of polarising material and the lines show the plane of polarisation. This plane of polarisation is parallel to the plane of polarisation in 2.

In the off position light passes through the window, first polariser (which plane polarises the light), electro-optic medium, second polariser and finally, into the area employing the shading system e.g. room.

5. When the system is switched on an applied voltage will pass through 3. 3 will then modulate the plane polarised light, which passes out of 2, in such a way that by the time it reaches the second piece of polarising material 4 it will effectively have a different plane of polarisation and because of this a cross polarising effect will occur when the light interacts with 4. This interaction between the light passing out of the electro-optic device 3 and the second polariser 4 is represented by 6.

6. When the maximum necessary applied voltage passes through 3 the interaction at 6 will be such that the greatest shading possible will occur. When the applied voltage is below the necessary maximum there will be a lesser degree of shading-the actual amount of shading depending on the applied voltage.

7. This shows the presence and direction light as it passes through the system.

8. This represents shaded light i.e. any light which has managed to pass through 4 when the electro-optical device is switched on.

FIG 4.

'POLARSHADE' AND DOUBLE GLAZING COMBINED Fig. 4 A to C shows the side views of double glazed windows with the incorporation of 'POLARSHADE' so as to form an integrated double glazed and shading system all in one unit.

FIG 4A. 'POLARSHADE' 1. Glass Window.

2. Double glazing gap with or without vacuum depending on the choice of double glazing to be installed.

3. Fixed polariser made of glass/glass laminate or other suitable double glazing material.

4. Sliding polariser. This does not form part of the double glazing arrangement.

FIG 4B 'POLARSHADE EO' 1. Glass Window.

2. Double glazing gap with/without vacuum.

4. Electro-optic device.

5. Fixed polariser.

NOTE: 3, 4 and 5 may consist of a single replaceable unit in which case its inner face will need to be made of a suitable double glazing material.

FIG 4C. 'POLARSHADE EO' 1. Glass window with laminated or attached fixed polariser.

2. Double glazing gap with/withoutva- cuum.

3. Electro-optic device.

4. Glass window with laminated or attached fixed polariser.

NOTE: In Fig 4C the middle section may be a single replaceable unit consisting of a polariser, double glazing gap, electro-optic device, double glazing gap and a second polariser in this order.

It will be apparent that provided the electrooptic device forms a seal between the two gaps a treble glazed effect will be created.

FIG 5 THE ELECTRO-OPTIC ROLLER BLIND TYPE SHADING SYSTEM (A) shows the window before the system is operated.

(B) shows the window at a stage where the variable switch has been turned so that the top half of the window is completely shaded by the electro-optic strips. (NOTE: the small clear gaps seen here will not exist in the working system since each of the electro-optic strips will rest directly below the next. They are merely shown in this diagram to highlight the electro-optic strips.

(C) shows the window at a stage where the variable switch has been turned so so that 43 of the window is shaded by the activated electro-optic strips.

It is noted that in this case the two other controls mentioned in the description are in use. These are: 1. The reverse switch Here the blind started shading from the bottom of the window working to a level i of the way up the window.

2. The voltage (shade) adjusting control has been varied so that in this particular case the degree of shading provided by the activated electro-optic strips has been lowered hence the grey colour of the strips.

FIG 6 THE ELECTRO-OPTIC VENETIAN BLIND TYPE SHADING SYSTEM STAGE this shows the height setting operation. Here only 3 electro-optic shutters are shown (though of course the working system will be made up of several shutters).

(2) and (3) show the width of the electrooptic shutters. Each of these are made up of 20 electro-optic strips (in this example). Since these do not operate at the height adjusting stage they are invisible.

(1 a) to (1 c) shows the height strips. These are visible here because the height adjusting control has been operated and the user has, in this particular case, decided that the height strip (1 c) should represent the lowest part of the window to be shaded. Therefore the two gaps (1 a) to (1 b) and (1 b) to (1 c) will be filled in (see stage 2) leaving the gap 3 completely clear.

STAGE this shows the filling in (shading) operation (4) shows some of the individual electrooptic strips which make up the shutters. Like the height strips these are only visible when the system is in use otherwise the window remains clear.

NOTE: The thin white lines between the these strips will not exist in the working system since each strip will rest directly below the next. They are merely shown in this diagram in order to highlight the electro-optic strips.

(5) shows that in this example the user only intends to shade the top half of each shutter leaving the bottom half (6) un-shaded.

Claims

1. A shade for a window or the like, comprising at least two sheets of relatively movable partially transparent material.

2. A shade as claimed in claim 1, wherein one of the sheets form the window.

3. A shade as claimed in claim 1 or 2, wherein the sheets consist of polarising material.

4. A shade as claimed in claim 3, wherein each sheet comprises a plurality of areas having different directions of polarisation, the areas forming a repeating pattern, relative movement of the sheets causing the patterns on adjacent sheets to move into and out of alignment.

5. A shade as claimed in claim 4, wherein the repeating pattern is such as to provide a plurality of relative sheet positions at which the light transmission properties of the shade are substantially constant across the sheets.

6. A shade as claimed in claim 1 or 2, wherein the sheets are patterned or textured such that relative movement of overlapping sheets generates variable interference patterns which provide for variable light transmission through the sheets.

7. A window shading system comprising a layer of electro-optic material.

8. A shading system as claimed in claim 7, further comprising a layer of polarizing material, said electro-optic material being a material which polarizes and/or rotates the plane of polarization of light.

9. A shading system as claimed in claim 7 or 8, wherein the electro-optic material is arranged to give a banding effect on the window to be shaded.

10. A shading system as claimed in claim 7, 8 or 9, wherein the electro-optic material is a liquid crystal.

11. A shading system as claimed in claim 7, wherein the electro-optic material is arranged in spaced parallel lines in each of two parallel planes.

12. A shading system as claimed in claim 7, wherein the electro-optic medium is arranged in a plurality of planes, one above the other, at an angle to a window or the like to be shaded.

13. A shade or screen for a window, substantially as hereinbefore described with reference to the accompanying drawings.

13. A shade for a window, substantially as hereinbefore described with reference to the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 to 13 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A shade or screen for a window or the like, comprising at least two sheets of relatively movable polarising material.

2. A device as claimed in claim 1, wherein one of the sheets forms the window.

3. A device as claimed in claim 2, wherein each sheet comprises a plurality of areas hav ing different directions of polarisation, the areas forming a repeating pattern, relative movement of the sheets causing the patterns on adjacent sheets to move into and out of alignment.

4. A device as claimed in claim 3, wherein the repeating pattern is such as to provide a plurality of relative sheet positions at which the light transmission properties of the shade are substantially constant across the sheets.

5. A shade or screen for a window or the like comprising a liquid crystal material.

6. A device as claimed in claim 5, wherein the liquid crystal is of an ordinary nematic, dynamic scattering type.

7. A device as claimed in claim 5, wherein the liquid crystal is of a twisted-nematic type, the said liquid crystal being positioned between two crossed linear polarisers.

8. A device as claimed in claims 5 to 7, wherein the voltage or electric field applied to the liquid crystal is made variable so as to permit a controlled variation of the amount of light transmitted through the window or the like.

9. A device as claimed in claims 5 to 8, wherein the liquid crystal material is arranged in adjacent strips which span the window vertically and/or horizontally, each strip or group of strips having its own separate pair of electrodes so that when an appropriate switching circuit and control pattern is incorporated in the device, it will appear to work in a manner similar to Venetian blinds, roller blinds, vertical louvre blinds or curtains.

10. A device as claimed in claim 9, wherein the said strips comprise a layer of a suitable electro-optic material.

11. A shading or screening system comprising an electro-optic material arranged in spaced parallel lines in each of two parallel planes.

12. A shading or screening system comprising an electro-optic medium arranged in a plurality of planes, one above the other, at an angle to a window or the like to be shaded or screened.