BACKGROUND ART As is known, electromagnetic waves constituting light radiation vibrate in a direction perpendicular to the direction of propagation, and, in the absence of polarizing phenomena, oscillate in all directions in the plane perpendicular to the direction of propagation. If, on the other hand, appropriate so-called polarizing devices are used to cause the waves to oscillate in one predetermined direction (and therefore in a plane parallel to the direction of propagation), light is said to be polarized in that direction: in other words, a ray of polarized light is composed of waves which all oscillate in the same plane (polarization plane).

Known light polarizing systems include so-called

Polaroid sheets, which are formed by depositing appropriate substances (e. g. quinine iodophosphate) on a transparent substrate. The substances may be deposited directly on the substrate (e. g. a sheet of glass) or on a film of polymer material which is then applied to the substrate. Normal light passing through the sheets emerges polarized in a predetermined direction.

Light polarization has been used in various applications, including the production of transparent variable-transparency elements : two circular sheets of glass with respective continuous polarizing layers are placed and rotate one on top of the other so as to continuously vary the angle between the polarization directions of the two layers. When the two layers are positioned so that the respective polarization planes coincide, light can pass through the layers; whereas, when the layers are positioned with the polarization planes perpendicular to each other, light is cut off completely. By rotating the layers with respect to each other between these two limit positions, the light intensity transmitted through the layers is varied continuously. Though practical and efficient, the system described briefly above is only suitable for producing small-size elements of a particular shape (only circular, such as portholes) and is therefore of extremely limited application.

To produce large-size transparent elements of any shape, sheets of glass are used in which liquid crystals

are dispersed and oriented in a predetermined direction by an electromagnetic field : the transparency of the element is varied by varying the orientation of the crystals. Though highly efficient, elements of this sort are extremely expensive, are difficult to produce, and, above all, require a relatively large amount of energy (to orient the crystals as required).

Other variable-transparency devices are made of electrochromic glass. These, however, are extremely expensive, involve highly complex manufacturing technology, and have a short working life due to poor thermal and ultraviolet ray stability.

DISCLOSURE OF INVENTION It is an object of the present invention to provide a light attenuating device designed to eliminate the aforementioned drawbacks typically associated with known devices, and which, in particular, is efficient, relatively cheap and easy to produce, and can be applied to transparent elements of different shapes and sizes.

According to the present invention, there is provided a light attenuating device, in particular for producing transparent variable-transparency elements, comprising a first and a second polarizing element, and actuating means for moving said first and said second polarizing element with respect to each other; the device being characterized in that said first and said second polarizing element in turn comprise respective first and second polarization portions; said respective first

portions having polarization planes differing from the polarization planes of said respective second portions; and said actuating-means moving said first and said second polarizing element with respect to each other so that said first portions of said second polarizing element are superimposed alternatively on said first and said second portions of said first polarizing element.

The device according to the invention thus provides for simply and effectively regulating the transmitted light intensity, is relatively cheap and easy to produce, and provides for producing transparent variable- transparency elements in a wide range of shapes and sizes. In particular, operation of the device is extremely straightforward (the relative movement of the polarizing elements may advantageously be a straightforward linear movement), and only a small amount of energy (e. g. electrical) is required to activate the device.

BRIEF DESCRIPTION OF THE DRAWINGS A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a purely schematic, partly sectioned view in perspective of the basic components of a light attenuating device in accordance with the present invention; Figures 2 and 3 show, schematically, the operating principle of the Figure 1 device.

BEST MODE FOR CARRYING OUT THE INVENTION Number 1 in Figure 1 indicates as a whole a light attenuating device-in the example shown, for producing a transparent variable-transparency element 2, e. g. a rectangular window.

Device 1 comprises a first and a second polarizing element 3,4; and actuating means 5 for moving polarizing elements 3,4 with respect to each other.

In the purely non-limiting example shown in Figure 1, polarizing elements 3 and 4 are in the form of flat rectangular sheets, and comprise respective numbers of first 6a, 6b and second 7a, 7b polarization portions oriented differently and therefore having different polarization planes. Here and hereinafter, the "polarization plane"of a polarizing element (i. e. any element capable of polarizing electromagnetic radiation and in particular light radiation) is intended to mean the plane in which vibrates predominantly or exclusively the electromagnetic radiation (in particular, the light radiation) passing through the polarizing element. The polarization plane defines, for a polarizing element, the orientation of the polarization assumed by the radiation passing through it.

Portions 6a, 7a of polarizing element 3 and corresponding portions 6b, 7b of polarizing element 4 are defined by respective rectangular transverse strips connected to one another along the respective major sides. Portions 6a, 7a of polarizing element 3 are

arranged alternately to form a succession of alternating portions 6a and 7a having different respective polarization planes in a predetermined direction 8; and, similarly, portions 6b, 7b of polarizing element 4 are arranged alternately to also form a succession of alternating portions 6b and 7b having different respective polarization planes in predetermined direction 8.

More specifically, portions 6a, 6b of both polarizing elements 3,4 have respective polarization planes perpendicular to the respective polarization planes of portions 7a, 7b. For example, portions 6a, 6b of both polarizing elements 3,4 all have respective horizontal polarization planes, while portions 7a, 7b all have respective vertical polarization planes.

Portions 6a, 6b, 7a, 7b of polarizing elements 3,4 are all defined by rectangular strips of the same size and which may therefore be superimposed on one another.

In particular, both portions 6a and portions 7a of polarizing element 3 can be superimposed alternatively on portions 6b and portions 7b of polarizing element 4, as shown clearly later on.

Polarization portions 6a, 6b, 7a, 7b may be formed using any known technique. In particular, as any skilled technician knows (and as also stated in the introduction to this disclosure), portions 6a, 6b, 7a, 7b may be formed by depositing appropriate polarizing agents, e. g. quinine iodophosphate, on a transparent substrate. The

polarizing agent may be deposited directly on a supporting substrate (e. g. a sheet of glass or transparent polymer material), or on a film of suitable polymer material which is then applied (e. g. bonded) to the substrate. Depositing the polarizing agent in predetermined directions also determines the corresponding polarization plane.

Other techniques, also referred to purely by way of example, by which to form the devices according to the invention include laminating the polarizing elements on inorganic substrates (e. g. glass sheets) or organic substrates (e. g. polymer, in particular PET, films) using adhesive films such as vinyl butyral resin or polyurethane; or encapsulating the sheets between sheets of glass and/or polymer films using thermal (vacuum or nonvacuum) lamination techniques, or various types of adhesive materials (acrylic, epoxy, polyurethane).

In other words, polarizing elements 3,4 and polarization portions 6a, 6b, 7a, 7b may be formed in any known manner. In particular, polarizing elements 3,4 may comprise respective supporting substrates (e. g. of glass or transparent polymer material) having polarizing layers formed, for example, by deposition of a polarizing agent such as quinine iodophosphate.

Polarizing elements 3,4 are inserted inside a supporting structure 10 defined, for example, by a frame 11 defining a through opening 12 closed by polarizing elements 3,4. Polarizing element 4 is mounted to slide

inside guides 13 formed inside frame 11, while polarizing element 3 is housed in a fixed position inside frame 11.

One end 14 of polarizing element 4 is connected to a known actuating member 15 (not shown in detail for the sake of simplicity) which, when activated by a control switch 16 (of any known type) controlling a motor 17 (e. g. electric), moves polarizing element 4 linearly, along guides 13 and therefore with respect to polarizing element 3, in a sliding direction coincident with the predetermined direction 8 in which portions 6a, 6b and 7a, 7b of polarizing elements 3,4 alternate.

Supporting structure 10 with guides 13, actuating member 15, control switch 16 and motor 17, which together define the actuating means 5 for moving polarizing elements 3,4 with respect to each other, may obviously be of any known type, and are therefore only described and illustrated purely schematically for the sake of simplicity.

Operation of device 1 according to the invention will now be described with reference also to Figures 2 and 3, in which any details similar to or identical with those already described are indicated using the same reference numbers.

In a first operating position shown in Figure 1 and corresponding to the situation shown schematically in Figure 2, polarizing elements 3,4 are so positioned that portions 6a of polarizing element 3 are aligned with and superimposed on portions 6b of polarizing element 4

having the same polarization as portions 6a, as shown schematically in Figure 2 by the lines (horizontal in the example shown) on portions 6a and 6b. Similarly, portions 7a of polarizing element 3 are aligned with and superimposed on portions 7b of polarizing element 4 having the same polarization, as shown schematically in Figure 2 by the lines (vertical in the example shown) on portions 7a and 7b.

In this situation, light beams 21, e. g. of natural (nonpolarized) light, pass through and are polarized by superimposed portions 6a, 6b in parallel polarization planes 22 (horizontal in the example shown schematically in Figure 2), and, likewise, pass through and are polarized by superimposed portions 7a, 7b in parallel (in the example shown, vertical) polarization planes 23, so that light beams 21 are allowed through transparent element 2 which, in this condition, is therefore substantially transparent.

Conversely, to prevent light from passing through transparent element 2, actuating member 15 is operated by means of control switch 16 and motor 17 to move polarizing elements 3,4 into a second operating position shown by the dash-and-dot line in Figure 1 and corresponding to the situation shown schematically in Figure 3, in which portions 6a of polarizing element 3 are aligned with and superimposed on portions 7b of polarizing element 4, and portions 7a of polarizing element 3 are aligned with and superimposed on portions

6b of polarizing element 4. In other words, differently oriented polarization portions of polarizing elements 3, 4 are superimposed (in the example shown, polarization planes perpendicular to one another), so that light beams 21 passing through portions 6a of polarizing element 3 are polarized in polarization planes 22 (Figure 3), whereas the light polarized in polarization planes 22 and passing through portions 7b of polarizing element 4 (which have polarization planes perpendicular to polarization planes 22) is cut off. The same also applies to light beams 21 passing first through portions 7a, by which they are polarized in polarization planes 23, and then through portions 6b, by which the light polarized in polarization planes 23 is cut off. In other words, light beams 21 are prevented from passing through transparent element 2, which, in this condition, is therefore substantially opaque.

Actuating means 5 enable the above operating positions of polarizing elements 3,4 to be alternated as required, and may obviously also be operated to set polarizing elements 3,4 to any number of intermediate positions between the above two operating positions and corresponding to different degrees of transparency (and hence transmitted light intensity) of transparent element 2.

Clearly, changes may be made to the device as described and illustrated herein without, however, departing from the scope of the present invention.

In particular, the polarization portions of polarizing elements 3,4 may be of any number, shape and size; different portions of polarizing elements 3,4 may be superimposed in numerous ways; each polarizing element 3,4 may have more than two series of differently polarized portions; and the polarization portions may obviously be oriented differently from those described herein purely by way of example.

Moreover, polarizing elements 3,4 may be defined by flexible polarizing films, e. g. inserted between nonpolarized rigid transparent sheets, in which case, only the films would be moved with respect to each other by actuating means 5.