WO2001084212A1

WO2001084212A1 - Improved microprism sheets and privacy screens utilizing same

Info

Publication number: WO2001084212A1
Application number: PCT/US2001/010812
Authority: WO
Inventors: Kenneth J. Myers
Original assignee: Greenberg, Edward
Priority date: 2000-04-27
Filing date: 2001-04-18
Publication date: 2001-11-08
Also published as: AU2001253115A1

Abstract

A privacy screen, an image separating screen suitable for creating stereoscopic images, and an image interlacing screen also suitable for use in creating stereoscopic images, are prepared by modifying a standard microprism sheet (1) of the type having a plurality of v-shaped grooves (2). The modifications may include altering the transmission properties of at least one surface (3, 4) of each groove (2) in such a manner that light transmitted in different directions has different properties, for example by attenuating light in one plane (3) and not in the second plane (4) to create a privacy screen, or by altering polarizations in at least one of the two planes (3,4).

Description

Improved Micropris Sheets And Privacy Screens Utilizing Same

This application is a continuation-in-part of U.S. Patent Application Ser. No. 09/583,731, filed March 30, 2000, and herein incorporated by reference, which is a continuation-in-part of U.S. Patent Application Ser. No. 09/481,942, filed January 13, 2000, and also incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to privacy screens that utilize microprism sheets, and to various improved microprism sheets which may be used as privacy screens.

Each of the preferred embodiments of the invention relates to microprism sheets of the type made up of a transparent substrate in which are formed linear grooves having planar surfaces which intersect to form a v-shaped cross-section, the two sets of planar surfaces ' on respective sides of the grooves being selectively arranged to block or alter light transmitted through the sheet.

More specifically, the invention has four principal embodiments : (i) The first principal embodiment relates to a privacy screen, and in particular to modification of a microprism sheet to emulate a privacy screen, to devices utilizing such a privacy screen emulation arrangement, and to methods of making a privacy screen.

(ii) The second principal embodiment relates to a privacy screen, and in particular to modification of a microprism sheet to emulate a privacy screen by differentially polarizing the different facets of the microprism sheet;

(iii) The third principal embodiment relates to combination of multiple privacy screens to provide a more specific field of view than can be obtained using a single privacy screen. (iv) The fourth' principal embodiment relates to modifications to microprism sheets by curving the sheets or varying individual facets to enable more accurate convergence of images by the sheets.

According to the first embodiment of the invention, a privacy screen is made up of a microprism transmission sheet. The microprism sheet of this embodiment is similar to the ones disclosed in U.S. Patent Nos. 2,909,770 (Pugsley)and 4,756,603 (Ohtani) in that one of the two surfaces or facets of a microprism made up of v-shaped grooves is altered to attenuate or scatter light incident on the surface or facet, but instead of attenuating all reflected light originating outside the image path, the modified microprism sheet of this embodiment attenuates or scatters polarized light that would normally be within the optical path from the image source to a viewer situated in front of the microprism sheet, thereb . roviding a louvre or privacy screen effect.

According to the second embodiment of the invention, the different facets of the microprism sheet of the first preferred embodiment of the invention are varied by applying a polarizing coating to at least one set of facets oriented at a first angle so that when polarized light passes through the facets, the facets with the polarizing coating block light transmission while the other set of facets does not. According to this embodiment, polarization of light entering the sheet may be achieved by applying a polarizing coating to the rear face of the sheet that is opposite the facets, although the sheet could also be used with a polarized light source rather than a polarized rear face.

According to the third embodiment of the invention, multiple privacy screens are arranged to provide a more limited field of view than can be provided by a single microprism sheet.

According to the fourth embodiment of the invention, microprism sheets are modified by varying the shape of individual facets, or by curving the sheets to change the direction of light transmission. This aspect of the invention may be used not only in connection with privacy screen applications, but in a wide variety of microprism applications, including image focusing and projection arrangements in general.

2 : Description of Related Art

Microprism sheets in the form of molded substrates with small prisms embedded within the material are well- known. The present invention involves various modifications or re-arrangements of a particular type of known microprism sheet in which a clear plastic material is formed with linear grooves, each having a v-shaped cross-section.

The prior art generally falls into one of two categories: (i) microprism sheets and devices using microprism sheets in which an image is uniformly transmitted through the microprism sheet, each facet of the microprism having identical light transmission properties and the facets being arranged in a uniform fashion across the sheet; and (ii) microprism sheets and devices utilizing microprism sheets in which one of the surfaces or facets of the microprisms in the sheet is altered in such a way as to reduce glare or reflections without affecting transmission of an image through the sheet.

The first category of prior art provides technical background concerning the materials and formation of microprism sheets and the manner in which light is transmitted through the sheets. Except as noted below, the materials and geometry of the sheets used in the preferred embodiments of the invention can easily be selected by those skilled in the art based on the principles disclosed in these patents, once the overall concepts of privacy screen emulation is understood. Examples of patents directed to microprism sheets in general, and to devices using microprism sheets, include the following: U.S. Patent Nos . 5,836,096 (Brauer) , 5,446,594 (Nelson et al . ) , 5,363,237 (Wakatake) , 5,316,359 (Lansinger) , 5,208,620 (Mitsutake et al . ) , 4,708,435 (Yata et al . ) , 4,309,074 (Granieri) , 4,309,073 (Nishimura et al . ) , 3,902,787 (Sherlock), and 4,206,969 (Cobb et al . ) . Each of these patents discloses transmission or projection devices that utilize microprism or Fresnel structures for the purpose of glare reduction or optimizing light transmission at all potential viewing angles. Also of general background interest is the transmission screen disclosed in U.S. Patent No. 5,317,405, which uses Fresnel microprism structures to transmit an image from a television while at the same time reflecting an image of the viewer to a camera, and U.S. Patent Nos. 5,835,661, 5,926,601 and 5,359,691, all to Tai et al . , which relate to light guide structures using microprisms. None of these patents discloses alteration of selected facets or surfaces in different intersecting planes to emulate a privacy screen or separate images according to the principles of the first and second embodiments of the present invention, the combination of multiple privacy screens according to the third preferred embodiment of the invention, or curvature of the sheets according to the fourth preferred embodiment of the invention. U.S. Patent No. 5,512,219 is of interest for its general disclosure of methods of ^■ making microprism sheets by casting, while U.S. Patent No. 3,718,078 (Plummer) is of interest for its description of the use of acid etching for the purpose of creating light diffusing surfaces for non- glare glass and for focusing screens for cameras ("focusing screens" are reflective surfaces used in cameras as disclosed in U.S. Patent No. 3,971,051 (Ruhle) ) . In addition, U.S. Patent No. 5,837,346 is of interest for its description of methods of making "bulk diffusion screens," which may configured for collimation "after the fashion of Fresnel lenses" and in which surface relief features may be formed by hot or cold embossing, by casting, or in any other way, and which may include reflective rear coatings formed by a particulate deposition process for use in front projection screens, or diffusion patterns created by photopoly erization. Those skilled in the art will appreciate that many of the methods of making or altering microprism sheets disclosed in these patents may also be used in making the microprism sheets of the preferred embodiments of the invention, and that the invention in its broadest form is not intended to be limited to any particular method of making or altering the sheets.

The second category of prior art includes U.S. Patent Nos. 2,909,770 (Pugsley) , 4,756,603 (Ohtani) , and 4,165,920 (Brown) , which describe arrangements in which one of the facets or surfaces of a microprism or Fresnel structure is altered by providing a light blocking or coating or treatment . These patents are most relevant to the first and second embodiments of the invention, in which a microprism sheet having linear grooves with a v-shaped cross-section is modified by altering the light transmission properties of at least one of the surfaces of each groove by attenuating or scattering light emitted in one direction. In particular, these patents describe the inclusion of light absorbing or scattering coatings or structures on selected microprism facets or surfaces, although they do not specifically suggest the use of such coatings or structures for the purpose of emulating a privacy screen, i.e., for altering the transmission properties of one of the surfaces or facets relative to another.

To the contrary, where image transmission is of concern in these patents, the microprisms tend to be arranged to increase the angles at which an image transmitted through the sheet is visible, even while limiting glare or reflections. Unlike the privacy screens of the first preferred embodiment of the invention, the glare reduction sheets disclosed in these patents seek to block only externally or internally reflected light and not to affect transmission of the image, whereas in the first embodiment of the invention, light is blocked in the path of the image to a viewer situated at a normal viewing angle. The privacy screens or stereoscopic imaging sheets of the invention, while superficially similar in structure to those used in the various embodiments of the present invention, are thus not to be confused with the glare reduction screens disclosed in this second category of patents, including the ones disclosed in U.S. Patent Nos. 2,909,770 (Pugsley) , 4,756,603 (Ohtani) , and 4,165,920

(Brown) .

The different functions of the prior microprism sheets having treated surfaces or facets manifest themselves in the different angles and arrangement of the microprism surfaces relative to those of the present invention. For example, U.S. Patent No. 2,909,770 (Pugsley) discloses a transmission screen for a projection television receiver, slide projector, or the like, in which a microprism-like structure includes two surfaces, one of which is oriented at a 45° angle so that light incident in the viewing direction is reflected away from the viewer, and the other of which is oriented parallel to the light transmission path so that it does not affect light transmission. To prevent multiple refractions and reflections of light off the microprism structure, the parallel (or "horizontal") surface of Pugsley is "coated with a black or light-absorbent substance 6, such, for example, as dull black paint." Because of its parallel orientation, the coated surface of Pugsley, even though similar to that of the invention, does not serve as a privacy screen, but rather is arranged so as to maximize absorption of reflected light and minimize absorption of transmitted light.

Similar glare or reflection suppressing transmission screen arrangements are disclosed in U.S. Patent No. 4,756,603 (Ohtani) and 4,165,920 (Brown). However, the arrangement of Brown is even less suitable than that of Pugsley for use as a privacy screen since Brown only coats a portion of the facets with an opaque material, while Ohtani discloses equally preferred alternatives involving treatment of a portion of the facets or the entire facets to reduce reflections, demonstrating a lack of concern or recognition of the potential to use the methods disclosed therein for privacy screening purposes. On the other hand, the Ohtani patent is of particular interest because, instead of coating the facets, the facets are altered by forming irregularities in the horizontal plane or at the peaks of the facets, the formation of irregularities being one of the methods that can be utilized to achieve the privacy screen of the first preferred embodiment of the invention

Similar glare reduction principles have also been applied to front projection screens, in which an image is projected onto the screen. For example, the structure disclosed in U.S. Patent No. 4,911,529 (Van De Ven) , includes a rear side reflective Fresnel or microlens structure and a front side Fresnel structure. Again, however, the facets of the front side Fresnel structure that are coated with a light absorbing material are parallel or "horizontal" facets rather than facets or surfaces through which the image would normally be transmitted to a viewer, and thus Van De Ven does not suggest a privacy screen effect, the purpose of the arrangement of Van De Ven being to prevent reflection of off-axis light that would blur the reflected image.

In general, the light absorbing materials used in the transmission screens of these patents must be placed on facets oriented perpendicular to the viewer, or to the image transmission path, so that they do not interfere with transmission or reflection of the image. The purpose of the transmission screen overlays of Pugsley, Ohtani, and Van De Van is essentially to optimize transmission or reflection of the image while suppressing ambient light that does not contribute to the image. Thus, even though microprism sheets are widely available and well-known, they have previously only been used in antiglare arrangements or in relatively complex light guiding or focusing devices. The possibility of modifying microprism sheets to form privacy screens has not previously been recognized. There is no known prior art involving the use of microprism sheets as privacy screens.

SUMMARY OF THE INVENTION

It is accordingly a first objective of the invention to extend the range of applications for microprism sheets to include a simple and inexpensive privacy screen, by modifying a standard microprism sheet of the type having a plurality of v-shaped grooves, to alter the transmission properties of at least one surface of each groove in such a manner that light transmitted in different directions has different properties and thereby create a privacy screen by attenuating light in one plane and not in the second plane

It is a second objective of the invention to provide a privacy screen that is simple to manufacture and that can easily be applied to a computer display or television so as to limit viewing of a displayed image to persons situated at a particular angle relative to the display or television.

It is a third objective of the invention to provide a simple and inexpensive privacy screen that can easily be applied to a computer display or television so as to selectively reveal portions of a displayed image to different viewers situated at different positions in front of the display or television.

It is a fourth objective of the invention to .provide novel applications for microprism sheets arranged to emulate a privacy screen, and to provide various methods of making such privacy screen emulating microprism sheets, including the use of light blocking, light diffracting, and light polarizing coatings.

It is a fifth objective of the invention to provide an arrangement of multiple privacy screens for the purpose of further harrowing the field of view relative to that provided by a single privacy screen and/or limiting the field of view in both a horizontal and a vertical direction.

It is a sixth objective of the invention to provide microprism sheets having a more controllable angle of convergence for use in a wide variety of applications involving microprism sheets.

These objectives are achieved, according to a first preferred embodiment of the invention, by modifying a microprism sheet of the above-described type, i.e., a microprism sheet having substantially linear, v-shaped grooves, so that one of the intersecting surfaces attenuates or scatters transmitted light, thereby forming a privacy screen which permits viewing of an image in the direction of the untreated surface and prevents viewing of the image through the treated surface. The microprism sheet may be used either as a screen overlay to prevent persons from viewing the image who are not positioned, directly in front of or at a specific angle relative to the screen, or in the form of a dual screen overlay to permit two persons to view different portions of an image displayed on a single screen.

Because of its simplicity and low cost, the privacy screens of this embodiment of the invention can be used in a wide variety of novel applications, such as to provide a screen overlay for two-player gaming applications. In such applications, the privacy screen blocks portions of an image in selected directions so that each player sees a different image. The objectives of the invention are further achieved, according to a second preferred embodiment of the present invention, by modifying a microprism sheet of the above type so that one set of facets oriented at a particular angle is coated with a filter that blocks light of a particular polarization. When the surface of the microprism sheet opposite the facets of the microprism is also coated, a privacy screen effect is obtained for ordinary unpolarized light. When only the one set of facets is coated, the privacy screen effect is obtained when the screen is placed in front of polarized light source or, alternatively, when polarized glasses are used to view the screen.

The objectives of the invention are also achieved, in accordance with a third preferred embodiment of the invention, by providing an arrangement of multiple superposed privacy screens arranged to more precisely control the angles at which viewing of images behind the privacy screen is permitted and/or to limit viewing with respect to both the horizontal and vertical directions.

Finally, the objectives of the invention are achieved, in accordance with the principles of the fourth embodiment of the invention, by modifying the construction of the microprism sheets to vary the shape of individual facets, or by curving the sheets to change the direction of light transmission. Although potentially useful in the context of privacy screening, it will be appreciated by those skilled in the art that this aspect of the invention may be used in a wide variety of microprism applications, including image focusing and projection arrangements in general .

In each of the embodiments of the invention involving treated surfaces, whether for purposes of creating a privacy screen or for creating a stereoscopic effect, the surfaces may be treated by coating, delustering, chemical or laser etching, or casting. In the case of chemical or laser etching, surfaces may be made opaque by roughening, either by applying the chemical or directing the laser at the surface through an appropriate mask, or by etching the casting tool or die that forms the sheet. Alternatively, surfaces cast with texturing or a satin finish may be differentially polished to transmit light in the desired direction.

According to yet another aspect of the invention, various non-optical coatings may be added to the privacy screen, such as an anti-radiation coating made up of ground lead as the diffusing agent and applied to either side of the microprism sheet. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1A is a top view of a microprism sheet arranged to emulate a privacy screen in accordance with the principles of a first preferred embodiment of the invention, in which x and y are horizontal axes respectively extending parallel to and perpendicular to the principal plane of the microprism sheet .

Fig. IB is an isometric view of the microprism sheet of Fig. 1A.

Fig. 2A is a top view of a two-player game application of the microprism sheet of Figs. 1A and IB.

Fig. 2B is an isometric view showing the manner in which the microprism sheet of Fig. 2A is arranged on a computer monitor or television.

Fig. 2C is a schematic diagram illustrating the operation of the two-player game application shown in Figs. 2A and 2B.

Figs. 2D and 2E are isometric views further illustrating the operation of the two-player game application shown in Figs. 2A and 2B. Fig. 3 is a schematic diagram illustrating a microprism sheet arranged to include at least one polarizing coating according to the principles of a second preferred embodiment of the invention.

Fig. 4 is a schematic diagram illustrating the use of multiple privacy screens to provide a more limited viewing area than is possible with a single privacy screen according to the principles of a third preferred embodiment of the invention.

Figs. 5A-5C are plan views of modifications of the microprism sheets shown in Figs. 2-6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figs. 1A and IB illustrate the manner in which a microprism sheet 1, which is of the type having v-shaped linear grooves 2 defined by surfaces 3 and 4 extending at respective angles α and β relative to an axis Y transverse to the principal plane of sheet 1, is arranged to emulate a privacy screen according to the principles of a first preferred embodiment of the invention. As illustrated, privacy screen emulation is obtained by modifying surfaces 3 so as to attenuate or scatter light transmitted therethrough. Except for the modification of surfaces 3 to attenuate or scatter light, microprism sheet 1 may be of conventional construction and materials. Modification of surfaces 3 can be carried out by any of the methods described in the prior patents cited above, including coating the surfaces with an opaque material and casting irregularities into the surfaces, or the surfaces may be modified by delustering, and/or chemical or laser etching. In the case of chemical or laser etching, surfaces may be made opaque by roughening,- either by applying the chemical or directing the laser at the surface through an appropriate mask, or by etching the casting tool or die that forms the sheet. In addition, or alternatively, surfaces originally cast with texturing or a satin finish could be polished to permit transmission of light, as could the planar rear surface of the microprism sheet, in which case the "altered" surfaces would be the light transmitting surfaces, or an additional printed black-and-white or color image could be applied to the light attenuating surfaces so that the person viewing the privacy screen would see the printed image rather than the image transmitted through the microprism sheet.

Because of the alteration of surfaces 3 to attenuate or scatter light transmitted therethrough (or the alteration of surfaces 4 to permit transmission of light) , only persons situated in the path of light transmitted through surfaces 4, represented schematically in Fig. 1A by an "eye" 5, will be able to view an image situated behind the microprism sheet 1. Anyone situated at an angle greater than β will have no line-o -sight to surfaces 4 and therefore be screened from the image.

The pitch of the grooves and angles of the respective planes will depend on the particular application. However, those skilled in the art will appreciate that the smaller the pitch, the less visible the grooves, for a smoother appearance. The angles at which viewing is optimal and/or at which a viewer will be unable to perceive an image will of course depend on the exact angles α and β of surfaces 3 and 4 and the index of refraction of the material from which microprism sheet 1 is constructed. In general, for a standard acrylic microprism sheet including parallel grooves having a pitch of .12 to .14 inches, an effective and practical privacy screen can be obtained if angle α is set at between 45° and 60°, and angle β is set at between 45° and 30° relative to axis Y. For example, a privacy screen effect can be achieved with a microprism sheet having a pitch of .13 inches, an angle α of 20°, and an angle β of 40° (i.e. 50° from the plane of the sheet) . In addition to screening an image from those who would otherwise be able to view the image through surfaces 3, those skilled in the art will appreciate that alteration of surfaces 3 will also have the benefit of reducing glare and improving the contrast of images transmitted through surfaces 4 according to the principles described, for example, in U.S. Patent Nos. 2,909,770 (Pugsley) and 4,756,603 (Ohtani), herein incorporated by reference. Those skilled in the art will appreciate that the difference between the microprism sheets disclosed by Pugsley and Ohtani and that of the preferred embodiment is that the altered surfaces of the microprism sheets of Pugsley and Ohtani are horizontal surfaces oriented so as not to affect transmission of the image to any potential viewer, whereas the altered surfaces of the microprism sheets of the preferred embodiment are visible to anyone situated outside a relatively narrow range of angles within which the transmitted image is intended to be viewed. Except for the orientation of the altered surfaces, the construction of the privacy screen of this embodiment may be similar to that used in the anti-glare screens of Pugsley and Ohtani.

When used as a screen overlay in the manner illustrated in Figs. 2A-2E, the microprism sheets may advantageously include an additional anti-radiation coating. For example, the microprism sheet may be coated with a compound including ground lead particles to protect viewers from radiation emitted by the display screen over which the microprism sheet is laid.

While Fig. IB illustrates the v-shaped grooves as being both linear and parallel, those skilled in the art will recognize that it is possible to provide a privacy- screening microprism sheet having grooves that curve, so as to extend the screening effect to three dimensions. Such an arrangement would not only frustrate eavesdroppers positioned to the right or left of a person viewing an image on the screen, but also prevent eavesdropping from above or below the person.

Alternatively, as illustrated in Figs. 2A and 2B, the microprism sheet may be arranged such that one portion 6 of the sheet is arranged to screen an image in one direction and a second portion 7 of the sheet is arranged to screen an image in a second direction. In this variation of the first preferred embodiment of the invention, the grooves 8 and 9 of respective portions 6 and 7 of the microprism sheet have light attenuating or scattering surfaces 10,11 oriented to prevent transmission of light to persons positioned on opposite sides of a plane bisecting the microprism sheet, and corresponding light transmitting surfaces that direct transmitted light to the appropriate positions. Those skilled in the art will appreciate that the term "portions" may refer to physically discrete sheets having respective grooves oriented in different directions and which are either joined together or simply located in • close proximity to each other, rather than a single sheet having grooves oriented in different directions.

The microprism sheet of this variation of the first preferred embodiment of the invention may be arranged as an overlay 12 for part or all of the screen of a computer monitor or television 13, as shown in Fig. 2B,^' and is especially suitable for use in connection with a two-player video game, as illustrated in Figs. 2C-2E. In particular, portion 6 of the microprism sheet illustrated in Fig. 2A is arranged to direct the first image 14 on the left side of the screen to first player 15 while screening image 14 from the second player 16. On the other hand, the portion 7 of the microprism sheet of the variation of the first preferred embodiment illustrated in Figs. 3A is arranged to direct a second image 17 to second player 16 while screening image 17 from first player 15.

As a result, different information or scenes can be provided to each player through the same monitor or television, so that player 15 sees the display illustrated in Fig. 2D while player 16, looking at the same monitor or television, sees the display illustrated in Fig. 2E. By way of example, a game could be devised in which scores or answers were provided to one player and not the other. Alternatively, the microprism sheet could be used in connection with more realistic two player fight or battle simulations, hide-and-seek games, or more traditional "board" games, in which each player is provided with a unique perspective. If the pitch of the grooves is made small enough, the grooves of the privacy screen will not be visible to either player even though the effects of the privacy screen will be immediately apparent.

A variation of the concept of altering one of the surfaces of a microprism sheet to diffract or block light to create a privacy screen is illustrated in Fig. 3. In the arrangement disclosed in Fig. 3, at least one of the surfaces 20 and 21 corresponding to surfaces 3 and 4 of the embodiment illustrated in Fig. 1 is altered to polarize light. When the rear surface 22 of the sheet is also coated with an polarization coating, or when the sheet is used in connection with a polarizing filter or other source of polarized light, or when viewed through a polarizing lens, a privacy screen effect corresponding to the effect obtained by the embodiments illustrated in Figs. 1A, IB, and 2A-2D may be obtained. According to the third preferred embodiment of the invention illustrated in Fig. 4, multiple privacy screens 24 and 25 are arranged to further limit the field of view of a person 5 looking through the sheets. The second sheet 25 may be arranged to have facets arranged at different angles than the first sheet 24, or grooves oriented at different angles so as to, for example, block light with respect to both vertical and horizontal axes.

Finally, as illustrated in Figs. 5A-5C, the microprism sheets used to interlace the images in any of the embodiments of Figs. 2-4 need not be planar microprism sheets with uniform facets. It is also within the scope of the invention to vary the size of the facets so as to focus or project images transmitted thereby, as illustrated in Fig. 5A, to curve the sheets to achieve similar effects, as illustrated in Fig. 5B, or to combine the concepts of varying the size of the facets and curving the sheets, as illustrated in Fig. 5C.

Although potentially useful in connection with privacy screen applications as described herein, the microprism sheet modifications illustrated in Figs. 5A-5C may be used in any context in which microprism sheets are conventionally used, and possibly in additional contexts. For example, if the microprism sheet of Fig. 5B is formed in a parabola shape, the microprism sheet can be used as a convenient focusing lens or collimator.

Having thus described a preferred embodiment of the invention in sufficient detail to enable those skilled in the art to make and use the invention, it will nevertheless be appreciated that numerous variations and modifications of the illustrated embodiment may be made without departing from the spirit of the invention. For example, a privacy screen or stereoscopic effect could be obtained for a reflected rather than transmitted image, and the privacy screen concept could be extended to light collection apparatus rather than just to image display devices. Accordingly, it is intended that the invention not be limited by the above description or accompanying drawings, but that it be defined solely in accordance with the appended claims .

Claims

What is claimed is :

1. A privacy screen, comprising: a microprism sheet including a substrate and a plurality of grooves having intersecting sides that form a v-shape, the sides of the grooves forming first and second sets of substantially planar surfaces oriented at non- zero angles relative to a plane extending transversely to a principal plane of the ^'microprism sheet, wherein the first set of substantially planar surfaces has light transmission properties that are different than corresponding light transmission properties of the second set of substantially planar surfaces so as to permit transmission of light from behind the screen to a first viewer situated in front of the screen along a first optical path through the screen, and to prevent transmission of light from behind the screen to a second viewer situated in front of the screen at a position different from that of the first viewer.

2. A privacy screen as claimed in claim 1, wherein the different light transmission properties include an opacity of the first and second sets of surfaces, wherein the first set of surfaces is transparent and the second set of surfaces is substantially opaque, and whereby a viewer situated along an optical path through the first set of surfaces may view an image transmitted by the microprism sheet but a viewer situated along an optical path through the second set of surfaces may not view the image .

3. A privacy screen as claimed in claim 1, wherein the different light transmission properties include a scattering coefficient, wherein light transmitted through the second set of surfaces is subjected to a higher degree of scattering than light transmitted through the first set of surfaces, and whereby a viewer situated along an optical path through the first set of surfaces may view an image transmitted by the microprism sheet but a viewer situated along an optical path through the second set of surfaces may not view the image .

4. A privacy screen as claimed in claim 1, wherein one set of facets of said microprism sheet is coated with a polarizing coating to achieve said light transmission prevention.

5. A privacy screen as claimed in claim 4, wherein a surface of said sheet opposite said one set of facets is also coated with a polarizing coating to provide a privacy screen effect using an un-polarized light source .

6. A privacy screen as claimed in claim 1, further comprising a second said microprism sheet superposed on the first microprism sheet, said second microprism sheet preventing transmission of light at a different angle from the first microprism sheet to further limit a viewing angle at which images are visible through the privacy screen.

7. A privacy screen as claimed in claim 1, further comprising an anti-radiation coating on one surface of the sheet .

8. A privacy screen as claimed in claim 1, wherein said anti-radiation coating includes ground lead.

9. A privacy screen as claimed in claim 1, wherein the microprism sheet is arranged as an overlay for a computer monitor or television.

10. A privacy screen as claimed in claim 1, wherein the microprism sheet includes two portions arranged such that each of two viewers situated in front of the screen is able to exclusively view a different portions of the 'screen.

11. A privacy screen as claimed in claim 1, wherein the first set of surfaces is coated with a light attenuating material .

12. A privacy screen as claimed in claim 1, wherein the first set of surfaces is textured.

13. A privacy screen as claimed in claim 1, wherein the second set of surfaces is polished and the first set of surfaces is not polished.

14. A microprism sheet including a substrate and a plurality of grooves having intersecting sides that form a v-shape, the sides of the grooves forming first and second sets of substantially planar surfaces oriented at non-zero angles relative to a plane extending transversely to a principal plane of the microprism sheet to form a plurality of facets, wherein dimensions of said facets vary between a center of a sheet and edges of said sheet .

15. A microprism sheet as claimed in claim 13, wherein a size of said facets increases towards the edges of said sheet .

16. A microprism sheet, comprising a plurality of parallel facets defined by grooves having intersecting sides that form a v-shape, wherein said sheet is non-planar.

17. A microprism sheet as claimed in claim 15, wherein dimensions of said facets vary between a center of a sheet and edges of said sheet .

18. A microprism sheet as claimed in claim 16, wherein a size of said facets increases towards the edges of said sheet .