Optical: systems and elements – Glare or unwanted light reduction – Directional or angular discrimination
Reexamination Certificate
2001-05-02
2002-09-03
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Glare or unwanted light reduction
Directional or angular discrimination
C359S614000, C359S601000, C359S602000, C359S606000
Reexamination Certificate
active
06443579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to field-of-view controlling arrangements, such as privacy screens, made up of microprism or lenticular sheets.
More particularly, the invention relates to a field-of-view controlling arrangement made up of a microprism or lenticular sheet having a plurality of sets of parallel surfaces that intersect to form prisms or lenticular structures, and in which field-of-view control or privacy screening is achieved by:
for sheets made up of parallel “one-dimensional” microprism or lenticular structures having at least two intersecting sets of mutually parallel surfaces, altering a first set of mutually parallel surfaces and at least one second set of the mutually parallel surfaces of the microprism or lenticular structures, and/or portions of the at least two sets of mutually parallel surfaces, by applying a light-attenuating treatment to the surfaces,
for sheets made up of “two-dimensional” or polyhedral lenticular structures having at least three intersecting sets of mutually parallel surfaces, or at least one set of curved surfaces extending in directions transverse to directions in which the field-of-view is to be limited, altering at least one set of the mutually parallel or curved surfaces by applying a light-attenuating treatment to the at least one set of mutually parallel or curved surfaces, and
for any type of microprism or lenticular sheet, including a diffusing agent in at least a portion of the sheet, and arranging the surfaces of the microprism or lenticular sheet so that light transmitted along selected optical paths is attenuated before exiting the sheet through a first set of surfaces while light transmitted along other optical paths is relatively unattenuated before exiting the sheet through a second set of surfaces oriented at a nonzero angle relative to each of the surfaces in the first set of surfaces,
thereby achieving a privacy screen that restricts viewing of an image from more than one side of the potential field-of-view.
The privacy screens of the invention represent an improvement over the privacy screens disclosed in copending U.S. patent application Ser. Nos. 09/583,731, filed Mar. 30, 2000, and 09/481,942, filed Jan. 13, 2000, (both incorporated herein by reference), which disclose privacy screens in which privacy screening is achieved by altering just one set of mutually parallel surfaces or facets of a conventional microprism sheet of the type having a single set of “one-dimensional” prisms, i.e., prisms formed by parallel grooves in the sheet, to attenuate light so as to restrict the field-of-view, for images transmitted by the sheet, to only one side of the field-of-view.
The privacy screens of the invention may be used as overlays for video displays, for example to restrict eavesdropping with respect to a computer display, or as window coverings. When used as window coverings, the privacy screens of the invention have the additional advantage that the prisms or lenticular structures that make up the screen may be used to bend incoming light and improve the view from the window. In addition, the privacy screens of the invention may, at desired angles, include embedded images or graphics, and may provide other screening functions such as attenuation of ultra-violet light or other radiation, polarization, and so forth.
2. Description of Related Art
As illustrated in
FIG. 1
, the privacy screen disclosed in copending U.S. patent application Ser. No. 09/481,942 is made up of a microprism sheet
1
having multiple sets of parallel surfaces
3
,
4
that intersect to form prisms defined by adjacent parallel grooves
2
.
In order to provide a privacy screening effect, one set of the parallel surfaces
3
is altered by surface treatment to attenuate or scatter transmitted light in selected directions. The result of this arrangement is a simple and inexpensive privacy screen that permits viewing of an image by an observer
25
through the untreated set of surfaces
4
, and that prevents viewing of the image through the treated sets of surfaces
3
, the angles &agr; and &bgr; of the respective surfaces determining the range of angles in which viewing is restricted. Uses for the privacy screen described in copending application Ser. No. 09/481,942 include computer monitor overlays that prevent eavesdropping, stereoscopic viewing devices, and two-player video game arrangements such as the one illustrated in
FIG. 3
, in which an overlay
12
consisting of multiple sheets
6
and
7
is used to restrict viewing by the respective game players of opposite portions of an image displayed on screen
13
.
Although the privacy screen described in U.S. patent application Ser. No. 09/481,942 is ideally suited to applications such as the one illustrated in
FIG. 3
, in which only one side of the field-of-view of an image needs to be restricted, applications such as eavesdropping prevention often call for restriction of viewing from at least two sides. Furthermore, it would be desirable if additional optical effects could be achieved with a single sheet, even if viewing from only one side need be restricted.
One solution to the problem of limiting viewing from more than one side of the field-of-view is proposed in the above-cited U.S. patent application Ser. No. 09/583,731. According to this solution, privacy screens identical to those described in U.S. patent application Ser. No. 09/481,942 are stacked with the treated sets of surfaces oriented in different directions to restrict the field-of-view of an image from multiple sides. While this solution is simple and effective, the present invention proposes two even simpler solutions, both involving use of a single rather than multiple microprism or lenticular sheets.
The two alternative solutions respectively involve use of surface treatment and bulk diffusion materials, and are discussed separately below.
Surface Treatment
The first alternative solution to the problem of restricting the field-of-view of an image from multiple sides is to use surface treatments similar to those described in the above-discussed U.S. patent application Ser. Nos. 09/481,942 and 09/583,731. However, instead of altering a single set of parallel surfaces or facets of a the microprism sheet to attenuate light so as to narrow the field-of-view of images passing through the sheet, the present invention proposes to achieve privacy screening by altering at least two of the sets of mutually parallel surfaces, portions of the at least two sets of mutually parallel surfaces, or a corresponding set of identically oriented curved surfaces, and in particular by applying a light attenuating surface treatment to the sets of mutually parallel or curved surfaces. The result of such treatment of multiple sets of surfaces is a privacy screen that restricts viewing of an image from more than one side of the potential field-of-view without the need to stack multiple sheets.
As discussed in detail in U.S. patent application Ser. No. 09/481,942, it is of course well-known in general to selectively treat surfaces of a microprism or lenticular structure for the purpose of selectively attenuating light passing through the sheet. However, such treatments had always been, prior to development of the privacy screen disclosed in U.S. patent application Ser. No. 09/481,942, used in a way that attenuates or scatters background light, rather than the image itself, so as to reduce glare or increase image visibility, contrast, or relative brightness. Furthermore, the prior microprism or lenticular structures had always been combined with other structures to form a rear or front projection screen, rather than being used as a stand-alone sheet or overlay used solely for the purpose of privacy screening.
The numerous prior patents disclosing treatment of microprism or lenticular surfaces to attenuate or re-direct background light for purposes of glare reduction, brightness and contrast optimization, or the like, thus tend to teach away from the invention, which involves intentional attenuation of the imag
Bacon & Thomas
Myers Kenneth
Sikder Mohammad
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