CA1278203C - Non-reflective image display device - Google Patents
Non-reflective image display deviceInfo
- Publication number
- CA1278203C CA1278203C CA000535569A CA535569A CA1278203C CA 1278203 C CA1278203 C CA 1278203C CA 000535569 A CA000535569 A CA 000535569A CA 535569 A CA535569 A CA 535569A CA 1278203 C CA1278203 C CA 1278203C
- Authority
- CA
- Canada
- Prior art keywords
- display device
- image display
- image
- angle
- prisms
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/02—Diffusing elements; Afocal elements
- G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
- G02B5/021—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
- G02B5/0231—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures the surface having microprismatic or micropyramidal shape
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B3/00—Simple or compound lenses
- G02B3/02—Simple or compound lenses with non-spherical faces
- G02B3/08—Simple or compound lenses with non-spherical faces with discontinuous faces, e.g. Fresnel lens
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/02—Diffusing elements; Afocal elements
- G02B5/0273—Diffusing elements; Afocal elements characterized by the use
- G02B5/0278—Diffusing elements; Afocal elements characterized by the use used in transmission
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/02—Diffusing elements; Afocal elements
- G02B5/0273—Diffusing elements; Afocal elements characterized by the use
- G02B5/0294—Diffusing elements; Afocal elements characterized by the use adapted to provide an additional optical effect, e.g. anti-reflection or filter
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/04—Prisms
- G02B5/045—Prism arrays
Abstract
NON-REFLECTIVE IMAGE DISPLAY DEVICE
Abstract of the Disclosure An image display device comprises an image to be displayed and a cover of substantially transparent material overlying and in optical contact with the image. The cover has a minutely textured outer surface such that the angle between a first vector normal to a randomly selected point on the surface; and, a second vector which passes through the selected point and which is normal to a plane tangential to the image at the point of intersection of the second vector with the image; has substantially unity probability of exceeding 45°.
An array of parallel, longitudinal right angle prisms of height exceeding about fifty times the wave-length of light provides a preferred non-reflective image cover.
Abstract of the Disclosure An image display device comprises an image to be displayed and a cover of substantially transparent material overlying and in optical contact with the image. The cover has a minutely textured outer surface such that the angle between a first vector normal to a randomly selected point on the surface; and, a second vector which passes through the selected point and which is normal to a plane tangential to the image at the point of intersection of the second vector with the image; has substantially unity probability of exceeding 45°.
An array of parallel, longitudinal right angle prisms of height exceeding about fifty times the wave-length of light provides a preferred non-reflective image cover.
Description
8~:)3 NO~-REFLECTIVE IMAGE DISPLAY DEVICE
Field of the Invention This application pertains to a non-reflective image display device whereby an image may be viewed in the absence of reflective glare.
Background of the Invention Images (for example, paintings, photographs, posters, prints and the like) are conventionally dis-played by mounting them beneath a protec-tive glass or plastic cover. Such covers reflect incident light into the observer's eyes, so the observer must subconsciously ignore reflected images which appear in the plane of the cover. Human observers naturally "train" themselves from an early age to subconsciously ignore re~lected images of this sort. However, the reflected images are always present and, in the case of particularly bright reflections, may inhibit the observer's ability to see the image clearly.
Various anti glare or anti-reflective image covers such as low glare glass are known in the prior art. However, these do not eliminate reflected glare;
they merely scatter reflected light in a multiplicity of directions, so that the observer does not perceive a sharp reflected image, but perceives only a substantial-ly blurred reflection, which is easier to subconsciously ignore. Unfortunately, even though the substantially blurred reElection is easier to ignore, it still very greatly reduces the level of contrast in the perceived image.
~ .
~LX'78;~V3 The prior art has also evolved a variety of anti-reflec-tive coatings such as those which are common-ly applied to camera lenses. However, such coatings are expensive and fragila. They are thus not well suited to use in general purpose image display situations.
The present invention provides an anti-reflec-tive image display device which substantially eliminates reflective glare, without blurriny or otherwise signifi-cantly distorting the quality of the displayed image,and which is relatively inexpensive and durable, thus rendering the invention well suited to use in a wide variety of image display situations.
Summary of the Invention The invention provides an image display device comprising an image to be displayed and a cover of sub-stantially transparent material overlying the image.
The cover has a minutely textured outer surface such that an angle 01 between a first vector normal to a randomly selected point on the surface; and, a second vector which passes through the selected point and which is normal to a plane tangential to the image at the point of intersection of the second vector with the image; has substantially unity probability of exceeding 45. Preferably, the outer surface is textured such that the probability distribution of the angle 01 for points on the outer surface is substantially 0 if 01 is less than 45; has a maximum value at a selected angle; and, is substantially 0 for values of 01 which differ from the selected angle by more than a selected deviation angle of less than about 10.
The cover is preferably also in optical con-8;~03 tact with the image. If such contact is impossible or undesirable then the cover may also have a minutely tex-tured inner surface such that an angle 02 between:
a third vector normal to a randomly selected point on the inner surface; and, a fourth vector which passes through the selected inner surface point and which is normal to a plane tangential to the image at the point of intersection of the fourth vector with the image; is greater than or equal to:
45 + 1/2(0 in ~ sin ((1/n)sin0 i )) where "n" is the refractive index of the cover mater-ial, and 0 i is the greatest angle for which it is true for substantially all points on the outer surface that 01 0min The average vertical displacement from the bottoms of recesses in the cover's outer surface, to the apices of protrusions from the cover's outer surface, preferably exceeds about fifty times the wavelength of light. Advantageously, the average vertical displace-ment aforesaid exceeds about .1 mm.
If protrusions from the cover's outer surface have apices of average width "e", then e/a is preferably less than about .02, where "a" is the average vertical displacement aforesaid.
Advantageously, the cover may comprise an ar-ray of parallel, longitudinal right angle prisms. A
substrate of thickness "b" may be provided between the prisms and the image which is to be displayed. The sub-strate cover may be removably optically contactible with the image.
If the cover has both inner and outer textured .. ~ xt7~3 surfaces then -those surfaces may each advantageously comprise an array of parallel, longitudinal prisms; the sides of each of the prisms preferably being inclined at an angle of about 63 with respect to a plane beneath each prism and tangential to the image.
The inven-tion also provides a "window" which may serve as an image display device or which may serve as a conventional window. The window comprises a sub-stantially transparent material having minutely texturedfirst and second surfaces which lie on opposed sides of a notional reference surface such that an angle 01 between: a first vector normal to a randomly selected point on the first surface; and, a second vector ~hich passes through the selected point and which is normal to a plane tangential to the reference surface at the point of intersection of the second vector with the reference surface; has substantially unity probability of exceed-ing 45; and wherein an angle 02 between: a third vector normal to a randomly selected point on the second surface; and, a fourth vector which passes through the selected second surface point and which is normal to a plane tangential to the reference surface at the point of intersection of the fourth vector with the reference surface; is greater -than or equal to:
45 + l/2(0 in ~ sin l((1/n)sin0 i )) where "n" is the refractive index of the window mater-ial, and 0 . is the greatest angle for which it is mln true for substantially all points on the first surface that 0 > 0 . -mln Brief Description of the Drawings Figure l is a cross-sectional side elevation view of a portion of a conventionally displayed image.
~X78;~03 Figure 2 is a cross-sectional side elevation view of a portion of an image display device according to the first embodiment of the invention.
Figure 3 is a cross-sectional side elevation view of a portion oE an image display device according to the second embodiment of the invention.
Detailed Description of the Preferred Embodiment Figure 1 depicts a prior art image display device in which an image 10 such as a painting, photo-graph, poster, print or the like is displayed beneath a protective sheet of transparent solid material (i.e.
glass) 12. Glass 12 may be in optical contact with im-age 10, or there may be a small air gap 14 between the inner surface of glass 12 and the outer surface of image 10. (By "optical contact", it is meant that any gaps between image 10 and glass 12 are very substantially less than the wavelength of light.) A human observer perceives image 10 by the reflection of incident light rays therefrom. An incident light ray "I" which strikes the outer surface of glass 12 is substantially refract-ed, along path "Rl", through glass 12 and is partially reflected, along path rl, away from the outer surface of glass 12. Those skilled in the art will readily ap-preciate that the fresnel reflectivity o-f glass having a refractive index n = 1.5 is such that at least 4% of the radiant energy of incident light ray I is reflected along path rl. When refracted ray Rl encounters the inner surface of glass 12, at least 4% of ray Rl is similarly reflected therefrom along path r2, the bal-ance being refracted through glass 12 toward image 10 along path R2.
~27~ 03 ~ hen reflected ray r2 encounters the outer surface of ylass 12, a major portion thereof is refract-ed through glass 12 along path R3, the balance (at least 4%) being reflected once again into glass 12.
~hen refracted ray R2 encounters the surface of image 10 it is reflected therefrom and the reflected ray (not shown) is similarly refracted and reflected by glass 12 to yield an emerying ray R4 (the intermediate refrac-tion and reflection paths are not shown). Ideally, -the radiant energy of emerging rays reflected by image 10, such as ray R4, is maximized; and, the radiant energy of emerging rays reflected by glass 12, such as rays rl and R3, is minimized. However, as explained above, a transparent glass cover reflects at least 4% of incident light ray I along path rl.
Consider now Figure 2 which is a side eleva-tion view of a portion of an image display device con-structed in accordance with the first embodiment of the invention. The image display device of Figure 2 com-prises a cover 16 having an outer surface formed of an array of parallel, longitudinal right angle prisms 20, 22, 24 ... 30 overlying and in optical contact with image 10. An incident light ray "I" which, for example, strikes the outer surface of prism 26 as illustrated in Figure 2 is substantially refracted through cover 16 along path Rl to image 10 and is partially (at least 4%) reflected along path rl toward prism 28. ~hen reflected ray rl encounters prism 28 it is in turn substantially refracted through prism 28 along path R2 and partially (at least 4%) reflected by prism 28 along path r2. If we assume the use of ideal materials to construct the image display devices of both Figures 1 and 2, then it will be appreciated that at least 4% of incident ray I is reflected along path rl in the prior ~.~78~3 art device of Figure 1. However, only a small portion of a small portion (i.e. at least 4% of a-t least 4%, or at least .16 percent) of incident ray I is reflected along path r2 in the embodiment of the invention il-lustrated in Figure 2. Accordingly, the intensity oflight re-flected from the outer surface of cover 16 is substantially diminished, thus allowing light reflected from the surface of image 10 to dominate the observer's perception.
Although it is expected that, in practice, the advantages aforesaid will be easily attainable with the aid of a cover comprising an array of parallel, longitu-dinal right angle prisms such as cover 16 illustrated in Figure 2, the use of prisms is not essential to attain the benefits of the invention. One need only place over and in optical contact with the image to be displayed a cover of substantially transparent material having a minutely textured outer surface such that an angle 01 between a first vector A normal to a randomly selected point on the surface; and, a second vector C
which passes through the selected point and which is normal to a plane tangential to the image at the point of intersection of the second vector with the image; has substantially unity probability of exceeding 45. (It will be noted that neither image 10 nor cover 16 need be flat). Because it is physically impossible to construct prisms (or other objects) having perfectly sharpened apices, there will be small rounded or flattened apices on the prisms (or on the other objects which yive the cover material its texture) where a normal vector will not satisfy the relationship aforesaid. However, such areas can be minimized; hence the use of the term "sub-stantially unity probability". Moreover, those skilled in the art will appreciate that the term "normal" is 8;~
used in relation to a surface in the sense that a vector is normal to the average slope of the surface over a characteristic distance which substantially exceeds the wavelength of light.
A preferred (but not essential) characteristic of the cover material, which assists in further obscur-ing any partially reflected images which may be present, is that its outer surface be textured such that the pro-Dability distribution of the angle ~1 for points onthe cover's outer surface is substantially 0 if 01 is less than 45; has a maximum value at a selected angle; and, is substantially 0 for values of ~1 which differ from the selected angle by more than a selected deviation angle of less than about 10.
To be optically effective it is necessary to ensure that the average vertical displacement from the bottoms of recesses in the outer surface of the cover material (i.e. the bottoms of the "V" grooves between adjacent prisms) to the apices of protrusions from the cover's outer surfacP (i.e. the apices of the prisms) exceeds about fifty times the wavelength of light. Ad-vantageously, the average vertical displacement afore-said exceeds about .1 mm. to inhibit entrapment ofparticulate matter between adjacent protrusions on the cover and facilitate cleaning of the cover's outer surface.
If the protrusions from the cover's outer sur-face have apices of average width "e" (i.e. "e" is a measure of the imperfection of the prisms or other ob-jects used to form the cover material) and if the aver-age vertical displacement aforesaid is "a" (see Figure 2) then the ratio e/a is less than about .02 in order to ~:7~
minimi~e reElection from the apices of the protrusions.
Advantageously, the cover material may further comprise a highly conformable substrate 32 of thickness "b" which may be placed in optical contact with the outer surface of the image to be displayed. To facili-tate re-use of the cover it may be removably optically contactible with the outer surface of the image. The dimension a+b is preferably less than about .5 mm.
where "a" is the vertical displacement aforesaid. This minimizes distortion of the image caused by viewing it through a prism.
As indicated above, a particularly preferred embodiment of the invention utilizes a cover of substan-tially transparent material comprising an array of par-allel, longitudinal right angle prisms. Optical light-ing film sold under the trade mark SCOTCHCAL by 3M Com-pany, St. Paul, Minnesota is a suitable form of such material. The prisms in that material have bases of about .07 inches and height o-f about .03 inches. A sub-strate about .15 inches thick adjoins the prism bases.
In some situations it may be impractical to place cover 16 in optical contact with image 10. For example, image 10 may be too valuable or too fragile to risk such contact. In such situations cover 16 may be provided with a minutely textured inner surface, as well as a textured outer surface of the sort described above. Cover 16 is then placed over image 10, leaving an air gap 14 between the inner surface of cover 16 and image 10 as shown in Figure 3 (which assumes the use of prisms to texture the inner and outer surfaces of cover 16). More particularly, the inner surface of cover 16 is preEerably textured such that an angle 02 between 78~0;~
a third vector D normal to a randomly selected point on the inner sur-face; and, a fourth vector F which passes through the selected inner surface point and which is normal to a plane tangential to a notional reference surface G located between the inner and outer surfaces of cover 16 (once ayain it is noted that neither imaye 10 nor cover 16 need be flat), at the point of intersec-tion of the fourth vector with the reference surface; is greater than or equal to:
45 + 1/2(~ - sin~l((l/n)sin0 )) min min where "n" is the refractive index of the cover mater-ial and 0 is the greatest angle for which it is min true for substantially all points on the outer surface that ~ . where 01 is the angle described above with reference to the outer surface of cover 16.
It can be shown that an especially interesting situation occurs where ~1 = 02 = about 63.
This angle satisfies the foregoing criteria. Moreover, since the prisms on both surfaces are equal, the optical clarity of cover 16 is enhanced. Furthermore, rays ori-ginating in the normal direction and refracted within cover 16 can be shown to be parallel to the opposed prism sides, hence facilitating extremely clear image transmission. It will readily be appreciated that the cover of Figure 3 is of general utility and may, for ex-ample, serve as a conventional window as well as part of an image display device of the sort depicted in Figure 3.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many al-terations and modifications are possible in the practice of this invention without departing from the spirit or 7~;~03 scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance de-fined by the following claims.
Field of the Invention This application pertains to a non-reflective image display device whereby an image may be viewed in the absence of reflective glare.
Background of the Invention Images (for example, paintings, photographs, posters, prints and the like) are conventionally dis-played by mounting them beneath a protec-tive glass or plastic cover. Such covers reflect incident light into the observer's eyes, so the observer must subconsciously ignore reflected images which appear in the plane of the cover. Human observers naturally "train" themselves from an early age to subconsciously ignore re~lected images of this sort. However, the reflected images are always present and, in the case of particularly bright reflections, may inhibit the observer's ability to see the image clearly.
Various anti glare or anti-reflective image covers such as low glare glass are known in the prior art. However, these do not eliminate reflected glare;
they merely scatter reflected light in a multiplicity of directions, so that the observer does not perceive a sharp reflected image, but perceives only a substantial-ly blurred reflection, which is easier to subconsciously ignore. Unfortunately, even though the substantially blurred reElection is easier to ignore, it still very greatly reduces the level of contrast in the perceived image.
~ .
~LX'78;~V3 The prior art has also evolved a variety of anti-reflec-tive coatings such as those which are common-ly applied to camera lenses. However, such coatings are expensive and fragila. They are thus not well suited to use in general purpose image display situations.
The present invention provides an anti-reflec-tive image display device which substantially eliminates reflective glare, without blurriny or otherwise signifi-cantly distorting the quality of the displayed image,and which is relatively inexpensive and durable, thus rendering the invention well suited to use in a wide variety of image display situations.
Summary of the Invention The invention provides an image display device comprising an image to be displayed and a cover of sub-stantially transparent material overlying the image.
The cover has a minutely textured outer surface such that an angle 01 between a first vector normal to a randomly selected point on the surface; and, a second vector which passes through the selected point and which is normal to a plane tangential to the image at the point of intersection of the second vector with the image; has substantially unity probability of exceeding 45. Preferably, the outer surface is textured such that the probability distribution of the angle 01 for points on the outer surface is substantially 0 if 01 is less than 45; has a maximum value at a selected angle; and, is substantially 0 for values of 01 which differ from the selected angle by more than a selected deviation angle of less than about 10.
The cover is preferably also in optical con-8;~03 tact with the image. If such contact is impossible or undesirable then the cover may also have a minutely tex-tured inner surface such that an angle 02 between:
a third vector normal to a randomly selected point on the inner surface; and, a fourth vector which passes through the selected inner surface point and which is normal to a plane tangential to the image at the point of intersection of the fourth vector with the image; is greater than or equal to:
45 + 1/2(0 in ~ sin ((1/n)sin0 i )) where "n" is the refractive index of the cover mater-ial, and 0 i is the greatest angle for which it is true for substantially all points on the outer surface that 01 0min The average vertical displacement from the bottoms of recesses in the cover's outer surface, to the apices of protrusions from the cover's outer surface, preferably exceeds about fifty times the wavelength of light. Advantageously, the average vertical displace-ment aforesaid exceeds about .1 mm.
If protrusions from the cover's outer surface have apices of average width "e", then e/a is preferably less than about .02, where "a" is the average vertical displacement aforesaid.
Advantageously, the cover may comprise an ar-ray of parallel, longitudinal right angle prisms. A
substrate of thickness "b" may be provided between the prisms and the image which is to be displayed. The sub-strate cover may be removably optically contactible with the image.
If the cover has both inner and outer textured .. ~ xt7~3 surfaces then -those surfaces may each advantageously comprise an array of parallel, longitudinal prisms; the sides of each of the prisms preferably being inclined at an angle of about 63 with respect to a plane beneath each prism and tangential to the image.
The inven-tion also provides a "window" which may serve as an image display device or which may serve as a conventional window. The window comprises a sub-stantially transparent material having minutely texturedfirst and second surfaces which lie on opposed sides of a notional reference surface such that an angle 01 between: a first vector normal to a randomly selected point on the first surface; and, a second vector ~hich passes through the selected point and which is normal to a plane tangential to the reference surface at the point of intersection of the second vector with the reference surface; has substantially unity probability of exceed-ing 45; and wherein an angle 02 between: a third vector normal to a randomly selected point on the second surface; and, a fourth vector which passes through the selected second surface point and which is normal to a plane tangential to the reference surface at the point of intersection of the fourth vector with the reference surface; is greater -than or equal to:
45 + l/2(0 in ~ sin l((1/n)sin0 i )) where "n" is the refractive index of the window mater-ial, and 0 . is the greatest angle for which it is mln true for substantially all points on the first surface that 0 > 0 . -mln Brief Description of the Drawings Figure l is a cross-sectional side elevation view of a portion of a conventionally displayed image.
~X78;~03 Figure 2 is a cross-sectional side elevation view of a portion of an image display device according to the first embodiment of the invention.
Figure 3 is a cross-sectional side elevation view of a portion oE an image display device according to the second embodiment of the invention.
Detailed Description of the Preferred Embodiment Figure 1 depicts a prior art image display device in which an image 10 such as a painting, photo-graph, poster, print or the like is displayed beneath a protective sheet of transparent solid material (i.e.
glass) 12. Glass 12 may be in optical contact with im-age 10, or there may be a small air gap 14 between the inner surface of glass 12 and the outer surface of image 10. (By "optical contact", it is meant that any gaps between image 10 and glass 12 are very substantially less than the wavelength of light.) A human observer perceives image 10 by the reflection of incident light rays therefrom. An incident light ray "I" which strikes the outer surface of glass 12 is substantially refract-ed, along path "Rl", through glass 12 and is partially reflected, along path rl, away from the outer surface of glass 12. Those skilled in the art will readily ap-preciate that the fresnel reflectivity o-f glass having a refractive index n = 1.5 is such that at least 4% of the radiant energy of incident light ray I is reflected along path rl. When refracted ray Rl encounters the inner surface of glass 12, at least 4% of ray Rl is similarly reflected therefrom along path r2, the bal-ance being refracted through glass 12 toward image 10 along path R2.
~27~ 03 ~ hen reflected ray r2 encounters the outer surface of ylass 12, a major portion thereof is refract-ed through glass 12 along path R3, the balance (at least 4%) being reflected once again into glass 12.
~hen refracted ray R2 encounters the surface of image 10 it is reflected therefrom and the reflected ray (not shown) is similarly refracted and reflected by glass 12 to yield an emerying ray R4 (the intermediate refrac-tion and reflection paths are not shown). Ideally, -the radiant energy of emerging rays reflected by image 10, such as ray R4, is maximized; and, the radiant energy of emerging rays reflected by glass 12, such as rays rl and R3, is minimized. However, as explained above, a transparent glass cover reflects at least 4% of incident light ray I along path rl.
Consider now Figure 2 which is a side eleva-tion view of a portion of an image display device con-structed in accordance with the first embodiment of the invention. The image display device of Figure 2 com-prises a cover 16 having an outer surface formed of an array of parallel, longitudinal right angle prisms 20, 22, 24 ... 30 overlying and in optical contact with image 10. An incident light ray "I" which, for example, strikes the outer surface of prism 26 as illustrated in Figure 2 is substantially refracted through cover 16 along path Rl to image 10 and is partially (at least 4%) reflected along path rl toward prism 28. ~hen reflected ray rl encounters prism 28 it is in turn substantially refracted through prism 28 along path R2 and partially (at least 4%) reflected by prism 28 along path r2. If we assume the use of ideal materials to construct the image display devices of both Figures 1 and 2, then it will be appreciated that at least 4% of incident ray I is reflected along path rl in the prior ~.~78~3 art device of Figure 1. However, only a small portion of a small portion (i.e. at least 4% of a-t least 4%, or at least .16 percent) of incident ray I is reflected along path r2 in the embodiment of the invention il-lustrated in Figure 2. Accordingly, the intensity oflight re-flected from the outer surface of cover 16 is substantially diminished, thus allowing light reflected from the surface of image 10 to dominate the observer's perception.
Although it is expected that, in practice, the advantages aforesaid will be easily attainable with the aid of a cover comprising an array of parallel, longitu-dinal right angle prisms such as cover 16 illustrated in Figure 2, the use of prisms is not essential to attain the benefits of the invention. One need only place over and in optical contact with the image to be displayed a cover of substantially transparent material having a minutely textured outer surface such that an angle 01 between a first vector A normal to a randomly selected point on the surface; and, a second vector C
which passes through the selected point and which is normal to a plane tangential to the image at the point of intersection of the second vector with the image; has substantially unity probability of exceeding 45. (It will be noted that neither image 10 nor cover 16 need be flat). Because it is physically impossible to construct prisms (or other objects) having perfectly sharpened apices, there will be small rounded or flattened apices on the prisms (or on the other objects which yive the cover material its texture) where a normal vector will not satisfy the relationship aforesaid. However, such areas can be minimized; hence the use of the term "sub-stantially unity probability". Moreover, those skilled in the art will appreciate that the term "normal" is 8;~
used in relation to a surface in the sense that a vector is normal to the average slope of the surface over a characteristic distance which substantially exceeds the wavelength of light.
A preferred (but not essential) characteristic of the cover material, which assists in further obscur-ing any partially reflected images which may be present, is that its outer surface be textured such that the pro-Dability distribution of the angle ~1 for points onthe cover's outer surface is substantially 0 if 01 is less than 45; has a maximum value at a selected angle; and, is substantially 0 for values of ~1 which differ from the selected angle by more than a selected deviation angle of less than about 10.
To be optically effective it is necessary to ensure that the average vertical displacement from the bottoms of recesses in the outer surface of the cover material (i.e. the bottoms of the "V" grooves between adjacent prisms) to the apices of protrusions from the cover's outer surfacP (i.e. the apices of the prisms) exceeds about fifty times the wavelength of light. Ad-vantageously, the average vertical displacement afore-said exceeds about .1 mm. to inhibit entrapment ofparticulate matter between adjacent protrusions on the cover and facilitate cleaning of the cover's outer surface.
If the protrusions from the cover's outer sur-face have apices of average width "e" (i.e. "e" is a measure of the imperfection of the prisms or other ob-jects used to form the cover material) and if the aver-age vertical displacement aforesaid is "a" (see Figure 2) then the ratio e/a is less than about .02 in order to ~:7~
minimi~e reElection from the apices of the protrusions.
Advantageously, the cover material may further comprise a highly conformable substrate 32 of thickness "b" which may be placed in optical contact with the outer surface of the image to be displayed. To facili-tate re-use of the cover it may be removably optically contactible with the outer surface of the image. The dimension a+b is preferably less than about .5 mm.
where "a" is the vertical displacement aforesaid. This minimizes distortion of the image caused by viewing it through a prism.
As indicated above, a particularly preferred embodiment of the invention utilizes a cover of substan-tially transparent material comprising an array of par-allel, longitudinal right angle prisms. Optical light-ing film sold under the trade mark SCOTCHCAL by 3M Com-pany, St. Paul, Minnesota is a suitable form of such material. The prisms in that material have bases of about .07 inches and height o-f about .03 inches. A sub-strate about .15 inches thick adjoins the prism bases.
In some situations it may be impractical to place cover 16 in optical contact with image 10. For example, image 10 may be too valuable or too fragile to risk such contact. In such situations cover 16 may be provided with a minutely textured inner surface, as well as a textured outer surface of the sort described above. Cover 16 is then placed over image 10, leaving an air gap 14 between the inner surface of cover 16 and image 10 as shown in Figure 3 (which assumes the use of prisms to texture the inner and outer surfaces of cover 16). More particularly, the inner surface of cover 16 is preEerably textured such that an angle 02 between 78~0;~
a third vector D normal to a randomly selected point on the inner sur-face; and, a fourth vector F which passes through the selected inner surface point and which is normal to a plane tangential to a notional reference surface G located between the inner and outer surfaces of cover 16 (once ayain it is noted that neither imaye 10 nor cover 16 need be flat), at the point of intersec-tion of the fourth vector with the reference surface; is greater than or equal to:
45 + 1/2(~ - sin~l((l/n)sin0 )) min min where "n" is the refractive index of the cover mater-ial and 0 is the greatest angle for which it is min true for substantially all points on the outer surface that ~ . where 01 is the angle described above with reference to the outer surface of cover 16.
It can be shown that an especially interesting situation occurs where ~1 = 02 = about 63.
This angle satisfies the foregoing criteria. Moreover, since the prisms on both surfaces are equal, the optical clarity of cover 16 is enhanced. Furthermore, rays ori-ginating in the normal direction and refracted within cover 16 can be shown to be parallel to the opposed prism sides, hence facilitating extremely clear image transmission. It will readily be appreciated that the cover of Figure 3 is of general utility and may, for ex-ample, serve as a conventional window as well as part of an image display device of the sort depicted in Figure 3.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many al-terations and modifications are possible in the practice of this invention without departing from the spirit or 7~;~03 scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance de-fined by the following claims.
Claims (27)
1. An image display device, comprising:
(a) an image to be displayed; and, (b) a cover of substantially transparent material overlying said image, said cover having a min-utely textured outer surface wherein an angle ?1 between:
(i) a first vector normal to a randomly selected point on said surface; and, (ii) a second vector which passes through said selected point and which is normal to a plane tangential to said image at the point of in-tersection of said second vector with said image;
has substantially unity probability of exceed-ing 45°.
(a) an image to be displayed; and, (b) a cover of substantially transparent material overlying said image, said cover having a min-utely textured outer surface wherein an angle ?1 between:
(i) a first vector normal to a randomly selected point on said surface; and, (ii) a second vector which passes through said selected point and which is normal to a plane tangential to said image at the point of in-tersection of said second vector with said image;
has substantially unity probability of exceed-ing 45°.
2. An image display device as defined in claim 1, wherein said cover is in optical contact with said image.
3. An image display device as defined in claim 1, wherein said outer surface is textured such that the probability distribution of said angle for points on said outer surface:
(a) is substantially 0 if said angle is less than 45°;
- Page 1 of Claims -(b) has a maximum value at a selected angle; and, (c) is substantially 0 for angles which differ from said selected angle by more than a selected deviation angle of less than about 10°.
(a) is substantially 0 if said angle is less than 45°;
- Page 1 of Claims -(b) has a maximum value at a selected angle; and, (c) is substantially 0 for angles which differ from said selected angle by more than a selected deviation angle of less than about 10°.
4. An image display device as defined in claim 3, wherein the average vertical displacement from the bot-toms of recesses in said surface, to the apices of pro-trusions from said surface, exceeds about 50 times the wavelength of light.
5. An image display device as defined in claim 3, wherein:
(a) protrusions from said surface have apices of average width "e"; and, (b) e/a is less than about .02, where "a" is the average vertical displacement from the bottoms of recesses in said surface to the apices of said protrusions.
(a) protrusions from said surface have apices of average width "e"; and, (b) e/a is less than about .02, where "a" is the average vertical displacement from the bottoms of recesses in said surface to the apices of said protrusions.
6. An image display device as defined in claim 3, wherein the average vertical displacement from the bot-toms of recesses in said surface, to the apices of pro-trusions from said surface, exceeds about .1 mm.
7. An image display device as defined in claim 3, wherein said cover further comprises a substrate of thickness "b" between said outer surface and said image.
8. An image display device as defined in claim 7, - Page 2 of Claims -wherein a+b is less than about .5 mm., where "a" is the average vertical displacement from the bottoms of re-cesses in said surface to the apices of protrusions from said surface.
9. An image display device as defined in claim 2, wherein said cover is removably optically contactible with said image.
10. An image display device as defined in claim 7, wherein said cover substrate is removably optically con-tactible with said image.
11. An image display device as defined in claim 2, wherein said cover comprises an array of parallel, long-itudinal prisms.
12. An image display device as defined in claim 11, wherein said prisms are right angle prisms.
13. An image display device as defined in claim 11, wherein the height of said prisms exceeds about 50 times the wavelength of light.
14. An image display device as defined in claim 11, wherein:
(a) said prisms have apices of average width "e";
and, b) e/a is less than about .02, where "a" is the height of said prisms.
(a) said prisms have apices of average width "e";
and, b) e/a is less than about .02, where "a" is the height of said prisms.
15. An image display device as defined in claim 11, wherein the height of said prisms exceeds about .1 - Page 3 of Claims -mm.
16. An image display device as defined in claim 11, wherein said cover further comprises a substrate of thickness "b" between said prisms and said image.
17. An image display device as defined in claim 16, wherein "b" is about .15 inches.
18. An image display device as defined in claim 16, wherein a+b is less than about .5 mm., where "a" is the height of said prisms.
19. An image display device as defined in claim 16, wherein said substrate is removably optically con-tactible with said image.
20. An image display device as defined in claim 11, wherein said prisms have a base of about .07 inches and a height of about .03 inches.
21. An image display device as defined in claim 1, said cover further comprising a minutely textured inner surface wherein an angle 02 between:
(i) a third vector normal to a randomly selected point on said inner surface; and, (ii) a fourth vector which passes through said selected inner surface point and which is nor-mal to a plane tangential to said image at the point of intersection of said fourth vector with said image;
is greater than or equal to:
- Page 4 of Claims -45° + 1/2(?min - sin-1((1/n)sin?min)) where "n" is the refractive index of said material, and is the greatest angle for which it is true for ?min substantially all points on said outer surface that ?1 > ?min.
(i) a third vector normal to a randomly selected point on said inner surface; and, (ii) a fourth vector which passes through said selected inner surface point and which is nor-mal to a plane tangential to said image at the point of intersection of said fourth vector with said image;
is greater than or equal to:
- Page 4 of Claims -45° + 1/2(?min - sin-1((1/n)sin?min)) where "n" is the refractive index of said material, and is the greatest angle for which it is true for ?min substantially all points on said outer surface that ?1 > ?min.
22. An image display device as defined in claim 21, wherein said inner and outer surfaces each comprise an array of parallel, longitudinal prisms.
23. An image display device as defined in claim 22, wherein the sides of each one of said prisms is in-clined at an angle of about 63° with respect to a plane beneath said one prism and tangential to said image.
24. A window comprising a substantially transpar-ent material having minutely textured, first and second surfaces on opposed sides of a notional reference sur-face, wherein an angle ?1 between:
(i) a first vector normal to a randomly selected point on said first surface; and, (ii) a second vector which passes through said selected point and which is normal to a plane tangential to said reference surface at the point of intersection of said second vector with said reference surface;
has substantially unity probability of exceeding 45°;
and wherein an angle ?2 between:
(iii) a third vector normal to a randomly selected point on said second surface; and, - Page 5 of Claims -(iv) a fourth vector which passes through said selected second surface point and which is normal to a plane tangential to said reference surface at the point of intersection of said fourth vector with said reference surface;
is greater than or equal to:
45° + 1/2(?min - sin-1((1/n)sin?min)) where "n" is the refractive index of said material, where ?min is the greatest for which it is true for substantially all points on said first surface that ?1 > ?min.
(i) a first vector normal to a randomly selected point on said first surface; and, (ii) a second vector which passes through said selected point and which is normal to a plane tangential to said reference surface at the point of intersection of said second vector with said reference surface;
has substantially unity probability of exceeding 45°;
and wherein an angle ?2 between:
(iii) a third vector normal to a randomly selected point on said second surface; and, - Page 5 of Claims -(iv) a fourth vector which passes through said selected second surface point and which is normal to a plane tangential to said reference surface at the point of intersection of said fourth vector with said reference surface;
is greater than or equal to:
45° + 1/2(?min - sin-1((1/n)sin?min)) where "n" is the refractive index of said material, where ?min is the greatest for which it is true for substantially all points on said first surface that ?1 > ?min.
25. A window as defined in claim 24, wherein said first and second surfaces each comprise an array of parallel, longitudinal prisms.
26. A window as defined in claim 25, wherein the sides of each one of said prisms is inclined at an angle of about 63° with respect to a plane beneath said one prism and tangential to said reference surface.
27. A window as defined in claim 24, wherein said surfaces are textured such that the probability distri-bution of either of said angles ?1 or ?2 for points on said surfaces:
(a) is substantially 0 if said angle is less than 45?;
(b) has a maximum value at a selected angle; and, - Page 6 of Claims -(c) is substantially 0 for angles which differ from said selected angle by more than a selected deviation angle of less than about 10°.
- Page 7 of Claims -
(a) is substantially 0 if said angle is less than 45?;
(b) has a maximum value at a selected angle; and, - Page 6 of Claims -(c) is substantially 0 for angles which differ from said selected angle by more than a selected deviation angle of less than about 10°.
- Page 7 of Claims -
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000535569A CA1278203C (en) | 1987-04-24 | 1987-04-24 | Non-reflective image display device |
| US07/169,292 US4883341A (en) | 1987-04-24 | 1988-03-17 | Non-reflective graphic surface |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000535569A CA1278203C (en) | 1987-04-24 | 1987-04-24 | Non-reflective image display device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1278203C true CA1278203C (en) | 1990-12-27 |
Family
ID=4135499
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000535569A Expired - Lifetime CA1278203C (en) | 1987-04-24 | 1987-04-24 | Non-reflective image display device |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4883341A (en) |
| CA (1) | CA1278203C (en) |
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| US4657355A (en) * | 1981-05-25 | 1987-04-14 | Masataka Negishi | Device for changing light width and direction |
-
1987
- 1987-04-24 CA CA000535569A patent/CA1278203C/en not_active Expired - Lifetime
-
1988
- 1988-03-17 US US07/169,292 patent/US4883341A/en not_active Expired - Lifetime
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| Publication number | Publication date |
|---|---|
| US4883341A (en) | 1989-11-28 |
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