WO2003042725A2

WO2003042725A2 - Optical film for high contrast displays

Info

Publication number: WO2003042725A2
Application number: PCT/US2002/029580
Authority: WO
Inventors: Gordon W. Gibbons; Andrew J. Piepel
Original assignee: 3M Innovative Properties Company
Priority date: 2001-11-09
Filing date: 2002-09-18
Publication date: 2003-05-22
Also published as: JP2005509894A; CN1592857A; EP1444537A2; TW591246B; AU2002331871A1; WO2003042725A3

Abstract

Optical systems and methods are disclosed that display information. Optical systems and methods include a light source and an optical film, where the optical film has low reflectance, controlled viewing angle, low glare and/or relatively high optical transmittance for diffuse incident light. Instrument cluster is disclosed that includes such an optical film. The optical film may include display graphics. The optical film may have higher optical transmittance for diffuse incident light than for collimated incident light.

Description

OPTICAL FILM WITH HIGH CONTRAST

FIELD OF THE INVENTION

This invention generally relates to electronic display components. The invention is particularly applicable to an instrument cluster display.

BACKGROUND Electronic displays generally display information to a viewer. The performance of a display is described in terms of various characteristics of the display. One such characteristic is the ability of the display to absorb ambient light originated from various sources of light such as a light bulb, the sun, and the viewer. Ambient light that is incident on a display, if not absorbed by the display, is superimposed on the displayed information resulting in reduced contrast generally referred to as washout. Washout is especially a concern in applications where ambient light is very bright. For example, in outdoor applications, ambient light from the sun can significantly reduce the display contrast thereby making it difficult for a viewer to discern the displayed information. A display, such as an instrument cluster, used in a motor vehicle is particularly susceptible to washout from sunlight. Typically, instrument clusters in a motor vehicle are recessed in a housing to reduce ambient light access to the display. The housing is generally made black to further reduce washout by reducing the amount of light that is reflected towards the front of the display from ambient light incident on the housing.

Another characteristic of a display is the amount of glare. A polished front surface of a display specularly reflects light incident from a nearby object towards the viewer.

Such specular reflection is generally referred to as glare and will reduce the viewability of the displayed information. Typically, glare from the front surface of a display is reduced by making the surface optically diffuse. Such diffuse surface is sometimes referred to as a matte surface. Generally, the front matte surface in a display is separated from the display's image plane, the plane where the image is displayed. Such separation reduces display resolution. It is generally desirable that the separation between the front matte surface and the image plane be minimized in order to minimize resolution loss. In that case the display resolution is not degraded by the front matte surface. Another characteristic of a display is the viewing angle. It is generally desirable that the displayed information be easily viewable over a predetermined range of viewing angles. In some applications, it is further desirable that the displayed information not be viewable outside the predetermined viewing range. In other words, it may be desirable to limit the viewability of a display to a particular and intended viewing position. Limiting the display viewability may be desirable for privacy considerations. Another setting where such limitation may be desirable is where viewability of the display by a person located outside the intended viewing position may interfere with the person's ability to perform a given task. For example, in a motor vehicle, it may be desirable that a display or an instrument cluster be viewable by the driver but not by other passengers as it may interfere with their comfort. Reflection of light from an instrument cluster off the windshield, side windows, or other glossy surfaces in a motor vehicle can be distracting to a driver. Limiting the viewing angle of the instrument cluster, for example to the driver's viewing position, can reduce or eliminate such reflections. Typically, the recessed housing of the instrument cluster may be designed to limit the viewing angle of the displayed information.

Another characteristic of a display is the overall footprint. Displays are generally desirable to have minimized depth in order to reduce overall volume of the display. For example, in reference to an instrument cluster in a motor vehicle, it may be desirable to minimize the recess in the instrument housing in order to save space or, for example, make room for accessories. As one display characteristic is improved, one or more other display characteristics often degrade. As a result, certain tradeoffs are made in a display in order to best meet the performance criteria for a given display application. Thus, there remains a need for displays with improved overall performance while meeting the minimum performance criteria.

SUMMARY OF THE INVENTION

Generally, the present invention relates to optical systems and displays. The present invention also relates to components in optical systems and displays. In one aspect of the invention an optical system includes a light source and an optical film. The optical film transmits light incident form the light source towards a viewer. The total optical transmittance of the optical film is higher for diffuse incident light than for collimated incident light.

In another aspect of the invention an optical system includes a light source and an optical film. The optical film transmits light incident from the light source towards a viewer. The optical film includes an optically absorptive layer and a plurality of optically transmissive beads. The beads are partially embedded in the optically absorptive layer such that a portion of the beads remain exposed to the viewer. A portion of light incident from the light source is transmitted by the optical film towards the viewer.

In still another embodiment of the invention an instrument cluster is described for displaying information to a viewing position. The instrument cluster includes an optically absorptive layer that and an optically transmissive substrate. A plurality of beads are partially embedded in the optically absorptive layer such that a portion of the beads remain exposed to the viewing position. Light incident from a light source onto the substrate is transmitted through the substrate and the beads towards the viewing position. The invention also provides a method for displaying information to a viewing ^' position. The method includes applying an optically absorptive layer onto an optically transmissive substrate. A plurality of optically transmissive beads are partially embedded in the optically absorptive layer such that a portion of the beads remain exposed to the viewing position. A portion of light incident onto the substrate from a light source is transmitted through the substrate and the beads towards the viewing position.

In still another aspect of the invention an optical film includes an optically transmissive substrate, an optically absorptive layer, a plurality of beads, and display graphics. The optically absorptive layer is applied onto the substrate. The beads are partially embedded in the optically absorptive layer such that a portion of the beads remain exposed to a viewing position. Display graphics are applied to the substrate and/or the beads. The optical film transmits light received from the substrate side through the beads towards the viewing position.

BREIF DESCRIPTION OF DRAWINGS The invention may be more completely understood and appreciated in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: Fig. 1 illustrates a schematic side view of an optical system in accordance with the invention;

Fig. 2 illustrates an embodiment of the invention which uses collimated incident light; Fig. 3 illustrates an embodiment of the invention which uses diffuse incident light;

Fig. 4 illustrates concepts of cone angle and viewing angle; Fig. 5 illustrates a schematic side view of an optical system in accordance with an embodiment of the invention;

Fig. 6A illustrates a magnified partial view of an optical film in accordance with one embodiment of the invention;

Fig. 6B illustrates optical transmittance of the optical film in Fig. 6A for collimated incident light;

Fig. 6C illustrates optical transmittance of the optical film in Fig. 6A for diffuse incident light; Fig. 7 illustrates a schematic side view of an optical system in accordance with another embodiment of the invention;

Fig. 8 illustrates a schematic frontal view of a display graphics; Fig. 9 illustrates a schematic frontal view of another display graphics; and Fig. 10 illustrates a schematic frontal view of yet another display graphics.

DETAILED DESCRIPTION The present invention is generally applicable to a number of electronic display applications and particularly to displays used in an environment where it is desirable for the display to absorb a substantial portion of the ambient light, have low specular reflectance, and/or have controlled viewing angle. The present invention is particularly suited for displays used in outdoors or in environments having very bright sources of ambient light. For example, one embodiment of present invention is well suited for use in an instrument cluster in a motor vehicle, a boat, a train, an air plane, and the like. In such applications, ambient light, glare, and uncontrolled viewing angle tend to interfere with viewing a display. While specific examples of the invention are described in detail below to facilitate explanation of various aspects of the invention, it should be understood that the intention is not to limit the invention to the specifics of the examples. Rather, the intention is to cover all modifications, embodiments, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Fig. 1 describes a schematic cross-section of an optical film 100 in accordance with one particular embodiment of the present invention. Optical film 100 is positioned between a light source 101 and a viewing position 150. The optical film has an input face 100 A and an output face 100B. Light originating from light source 101 and incident onto optical film 100 enters the optical film through input face 100A and is transmitted by the optical film. The transmitted light exits optical film 100 through output surface 100B towards viewing position 150. Ray 103 schematically represents ambient light present on the viewer side of optical film 100 and incident on output face 100B of said optical film.

Optical film 100 in accordance with one particular embodiment of the present invention has a higher total optical transmittance for diffuse incident light than for collimated incident light, where the incident light originates from light source 101. Furthermore, optical film 100 has a total optical absorption of more than 50% for diffuse light incident on output face 100B from the viewing side. In some instances the total optical absorption may be more than 60%. In still other instances the total optical absorption may be more than 70%. In addition, in one particular embodiment of the present invention the viewing angle of light transmitted by optical film 100 for diffuse incident light, incident light originating from light source 101, is less than the half cone angle of the incident light.

Optical film 100 in accordance with one particular embodiment of the invention incorporates a structure which creates an image plane that is on the output face 100B that further serves as an anti-glare structure. In other words, the structure provides a diffuse surface 400B thereby reducing or eliminating the need for additional anti-glare treatment of surface 400B. As a result, optical film 100 has a higher optical transmittance for diffuse incident light than collimated incident light and incorporates an output surface 400B that has very low specular reflectance. The specular reflectance for optical film 100 is typically less than 2%. In some instance the specular reflectance is less than 1%. In still other instances the specular reflectance is less than 0.05%. Light originating from light source 101 and incident onto input face 100A of optical film 100 may be collimated or diffuse as described more fully below. Fig. 2 schematically illustrates the total optical transmittance of an optical film 200 for a collimated incident light. Optical film 200, having an input face 200A and an output face 200B, is positioned between a light source 201 and a viewing position 250. Rays 202 are substantially parallel with one another and constitute an array of collimated light rays originating from light source 201 and incident onto input face 200 A of optical film 200. An incident ray 202 A makes an incident angle α with axis 210 where axis 210 is the normal to input surface 200A. As illustrated in Fig. 2, rays 202 have a non-zero incident angle. In general, the incident angle of rays 202 may assume any value from -90 degrees to + 90 degrees. Rays 202 are transmitted by optical film 200 and exit the optical film through output surface face 200B towards viewing position 250. The total optical transmittance of optical film 200 for a collimated incident light is calculated by dividing the total optical power exiting optical film 200 by the total optical power incident on the optical film and originating from light source 201.

Fig. 3 schematically illustrates the total optical transmittance of an optical film 300 for a diffuse incident light. Optical film 300, having an input face 300 A and an output face 300B, is positioned between a light source 301 and a viewing position 350. Rays 302 constitute an array of diffuse light rays originating from light source 302 and incident onto input face 300A of optical film 300. An incident ray 302A makes an incident angle β with axis 310 where axis 310 is the normal to input surface 300A. In general, for a diffuse incident light different rays have different incident angles. The incident angle for a given incident ray 302A may assume any value from -90 degrees to + 90 degrees. Rays 302 are transmitted by optical film 300 and exit the optical film through output face 300B towards viewing position 350. The total optical transmittance of optical film 300 for a diffuse incident light is calculated by dividing the total optical power exiting optical film 300 by the total optical power incident on the optical film and originating from light source 301.

Referring back to Fig. 1, optical film 100 in accordance with one particular embodiment of the present invention has a greater total transmittance for a diffuse incident light than for a collimated incident light.

To further describe a property of optical film 100 according to the invention, Fig. 4 illustrates the concepts of cone angle and viewing angle as used herein. Optical film

400, having an input face 400 A and an output face 400B, is positioned between a light source 401 and a viewing position 450. Rays 402 constitute an array of all light rays incident onto a point 400C positioned on input face 400A of optical film 400. Point 400C is designated by the symbol "X". The incident cone angle is the angle between extreme rays 402A and 402B and is designated by the symbol γin Fig. 4. Incident rays 402 are transmitted by optical film 400 and exit the optical film through output surface 400B as rays 403. Transmitted rays 403 constitute an array of light rays having a brightness profile. The viewing angle is the angle at which brightness drops to half of the peak brightness and is designated by the symbol ω in Fig. 4.

Referring back to Fig. 1, optical film 100 in accordance with one particular embodiment of the present invention transmits an incident cone of light in such a way that the viewing angle of the transmitted light is less than the half cone-angle of the incident light.

One particular embodiment of the optical film element of Fig. 1 is schematically shown in Fig. 5. Optical film 500 is positioned between a light source 501 and a viewing position 550. Light is incident onto the optical film from light source 501 and exits the optical film towards viewing position 550. Optical film 500 includes a substrate 510, a light absorbing layer 520, a plurality of beads 530, and an optional optical layer 540. Substrate 510 has an input face 510A and an output face 510B. Input face 510A faces light source 501. The exposed surfaces of beads 530 face viewing position 550 and any ambient light 504 that may be present. The particular embodiment of the invention as illustrated in Fig. 5 displays light received from light source 501 to viewing position 550 with high contrast, reduced glare, and generally, with controlled viewing angle.

Optical films similar in construction to optical film 500 of Fig. 5, have been previously described for use as a rear projection screen in a rear projection display. An example is disclosed in US Patent 5,563,738. When used as a rear projection screen, optical film 500 is disposed between a light source and a viewing position in such a way that exposed surfaces of beads 530 face the light source while the substrate faces the viewing position. In this construction, incident light originating from the light source must generally be collimated to optimize total optical transmittance of the projection screen. In contrast, according to an embodiment of the present invention, the light source is located on the substrate side of the optical film and the exposed beads face the viewing position.

In this construction, incident light originating from the light source is preferably diffuse to maximize total optical transmittance of the optical film. When used as a projection screen, beads in a film like that disclosed in US patent 5,563,738 act as focusing lenses requiring collimated incident light for efficient focusing and transmittance of the incident light. The total optical transmittance of the projection screen disclosed in US patent 5,563,738 generally decreases as the incident light becomes more diffuse. In contrast, in one embodiment of the present invention beads 530 of optical film 500 function to partially collimate the incident light. The collimation is more efficient for diffuse incident light, according to this embodiment of the present invention, and the total optical transmittance of the optical film generally increases as the incident light becomes more diffuse. Optical film 500 according to one embodiment of the present invention transmits diffuse light incident from the light source with high efficiency, absorbs a substantial portion of the ambient light, and has very low specular reflectance from the viewer side, thereby displaying information to viewing position 550 with high contrast.

One advantage of using a film in the configuration of Fig. 5 is that it is easier to design and manufacture a light source having diffuse light output than collimated light output. Furthermore, it is generally easier to diffuse a collimated light source than to collimate a diffuse light source. This is especially the case if the light source is an extended light source and not a point light source. The output of a diffuse light source is typically collimated by employing additional optical elements such as optical lenses. For example, in a rear projection display a fresnel lens is employed to collimate output light of the light source. A distinct advantage of the above embodiment of the present invention is that the total optical transmittance of the optical film increases as the incident light becomes more diffuse. Therefore, the optical film is particularly well suited for use with a diffuse light source including a diffuse extended light source. Referring back to Fig. 5, optically absorptive layer 520 is disposed onto output surface 510B of substrate 510. Beads 530 are partially embedded in layer 520. It is desirable that beads 530 be in close proximity or optical contact to surface 510B in order to increase the overall optical transmittance of optical film 500. Light absorbing layer 530 surrounding bead 530 in regions close to output face 510B defines an effective entrance aperture 531 for light received by the bead from light source 501. A ray 502 incident from light source 501 onto input surface 510 A and making an incident angle α with the normal to surface 510A is refracted at interface 510A and transmitted through bead 530 and optical layer 540. The transmitted ray exits optical film 500 as ray 503 making an angle β with the normal. Exit angle β is primarily determined by , the index of refraction of bead 530, and the index of refraction of substrate 510. Because of the collimating effect of beads 530 angle β is generally less than angle α. Hence, for a diffuse light incident onto optical film 500 and originating from light source 501, the viewing angle of the transmitted light is generally less than the half incident cone angle of the incident light. Furthermore, the total optical transmittance of optical film 500 for a diffuse incident light is greater than for collimated incident light. This is further described with reference to Figs. 6 A, 6B, and 6C. With reference to Fig. 6 A, an optical film 600, similar to the optical film of Fig.

5, is positioned between a light source 601 and a viewing position 650. Light is incident onto the optical film from light source 601 and exits the optical film towards viewing position 650. The optical film 600 includes a substrate 610, a light absorbing layer 620, and a plurality of beads 630. The optional optical layer 540 of Fig. 5 is not included in Figs. 6A-6C for ease of illustration and without any loss of generality. Substrate 610 has an input face 610A and an output face 610B. Input face 610A faces light source 601. The exposed surfaces of beads 630 face viewing position 650. Light absorbing layer 620 surrounding bead 630 in regions close to output face 610B defines an effective entrance aperture 631 for light received by the bead from light source 601. The exposed surface of bead 630 forms an exit aperture 632 which is generally larger than entrance aperture 631.

Entrance aperture 631, in part, determines the amount of light transmitted by bead 630 for light received from light source 601.

Fig. 6B illustrates the total optical transmittance of optical film 600 for a collimated incident light. Rays 633 constitute an array of collimated light rays originating from light source 601 and incident onto output surface 610B. It can be appreciated from

Fig. 6B that only those incident rays, such as ray 633B, which fall within entrance aperture 631, are transmitted by bead 630. On the other hand, rays 633 A and 633C, which fall outside entrance aperture 631, are significantly absorbed by optically absorptive layer 620 and are not transmitted to viewing position 650. The total optical transmittance of optical film 600 for a collimated light incident on input surface 610A is typically less than

25%. In some instances the total optical transmittance is less than 20%. In still some other instance the total optical transmittance is less than 15%. The viewing angle of light exiting optical film 600 for a collimated incident light is, in part, determined by the index of refraction of bead 630 and the size of entrance aperture 130, which in turn is, in part, determined by the diameter of bead 630 and the optical absorption coefficient of optically absorptive layer 620. For beads 630 having an index of refraction in the range 1.5 to 1.7 and mean diameter of approximately 60 microns, and an optically absorptive layer having an optical absorption coefficient in the range 0.4 to 0.6 inverse micron, the viewing angle of the transmitted light for a collimated incident light is generally less than 30 degrees. Fig. 6C illustrates the total optical transmittance of optical film 600 for diffuse incident light. Rays 635 constitute an array of diffuse light rays originating from light source 101 and incident onto entrance aperture 631. The incident rays have a half incident cone angle of γ. Rays 635 are transmitted through entrance aperture 631, refract at exit aperture 632, and are directed towards viewing position 650 with a viewing angle of ω where co is generally less than γ due to collimating effect of bead 630. It can be appreciated from Fig. 6C that the total optical transmittance of optical film 600 generally increases as the incident light becomes more diffuse or, equivalently, as the incident half cone angle γ increases. This is the case since for a constant light power density, a larger portion of an incident light is transmitted through entrance aperture 631 as γ increases. Total optical transmittance of optical film 600 for diffuse light incident on input face 610A of the optical film is typically more than 20%. In some applications the total optical transmittance is more than 30%. In still some other applications the total optical transmittance is more than 40%. In still some other applications the total optical transmittance is more than 50%. Rays 635 may be diffuse when leaving light source 601. Alternatively, rays 635 may be collimated or less diffuse when leaving light source 601 and become diffuse or more diffuse after being transmitted through an optically diffusive substrate 610. Alternatively, an additional optically diffusive layer, not shown in Fig. 6, may be placed between substrate 610 and light source 601 to diffuse light originating from light source 601.

Referring back to Fig. 5, the total optical transmittance of optical film 500 generally increases as the incident light becomes more diffuse. In addition, for a diffuse light incident onto optical film 500 and originating from light source 501, the viewing angle of transmitted light is generally less than the incident half cone angle. Hence, for a diffuse light source or for a specular light source combined with a diffuse substrate 510, or for a specular light source combined with an optical diffuser not shown in Fig. 5, optical film 500 displays high optical throughput with narrowed viewing angle. The property of narrow viewing angle of optical film 500 is particularly useful in design of an instrument cluster used in a boat, airplane, motor vehicle, or the like. In the case of a motor vehicle, the viewing angle of a conventional display in an instrument cluster is usually quite large.

As a result, light from the display can reach the front windshield and side windows and be reflected towards the driver or other passengers causing glare. To reduce the viewing angle, instrument clusters are usually recessed in a housing resulting in increased footprint of the motor vehicle dashboard. Incorporating optical film 500 into an instrument cluster reduces the viewing angle of the displays used in the instrument. Hence, there is little or no need for recessing the displays in a housing.

Light absorbing layer 520 is designed to absorb a substantial portion of ambient light incident onto the viewer side of optical film 500. With reference to Fig. 5, an ambient ray 504 enters optical layer 540 from the viewer side and is transmitted through bead 530 into optically absorptive layer 520 where it is substantially absorbed. Optical film 500 absorbs a substantial portion of ambient light, thereby displaying information with high contrast to viewing position 550 even in the presence of high ambient light. For example, an instrument cluster in a motor vehicle incorporating optical film 500 absorbs a substantial portion of ambient light, thereby displaying information, for example to a driver, with high contrast even in the presence of high ambient light. The optical absorption of optical film 500 for light incident from the viewing side depends, in part, on the absorption coefficient and thickness of optically absorptive layer 520. The optical absorption coefficient of the optically absorptive layer may be in the range 0.01 to 10 inverse microns. More preferably, the absorption coefficient is in the range 0.1 to 5 inverse microns. Even more preferably, the optical absorption coefficient is in the range

0.3 to 1 inverse microns. The thickness of the optically absorptive layer is, in part, determined by the average size of beads 530 and the standard of deviation of bead size. The thickness of the optically absorptive layer may be in the range O.lr to 0.9r where r is the average radius of beads 530. In some instances this thickness may be in the range 0.3r to 0.7r. In still other instances this thickness may be in the range 0.4r to 0.6r.

It is desirable that beads 530 form a single layer with high packing density to optimize overall transmittance of optical film 500, although in some applications multilayer beads may be used. A particularly advantageous property of optical film 500 is that the surface of beads 530 form a matte surface on the output side of the optical film facing the viewer. In other words, beads 530 transmit diffuse incident light towards viewing position 550 with high throughput and high contrast, while at the same time beads 530 form a matte surface. The matte surface reduces or eliminates glare (i.e., has a very small specular reflectance). In accordance to one embodiment of the invention, the matte finish of output surface of the optical film reduces or eliminates the need for additional anti-glare treatment of the optical film. In applications where the image plane (i.e., the plane where the image is displayed) is in close proximity to or coincident with beads 530, there is little or no loss of resolution due to matte surface of the output side of optical film

500. The reduction in glare, achieved by exposed surfaces of beads 530, depends primarily on bead size and bead size distribution. Generally, smaller beads are more effective in reducing glare or specular reflection. Specular reflectance of optical film 500 from the viewer side is typically less than 2%. In some instances the specular reflectance is less than 1%. In still other instances the specular reflectance is less than 0.05%.The very low specular reflection of optical film 500 makes the film well suited for use in display applications where glare is highly undesirable. Optical film 500 is especially suited for displays used outdoors or in applications where very bright ambient light can result in significant and highly undesirable glare. For example, an instrument cluster in a motor vehicle that incorporates optical film 500 significantly reduces or eliminates glare with little or no need for additional anti-glare treatment. Furthermore, where beads 530 constitute the image plane, or are in close proximity to the image plane, there is no or little loss of resolution. In the absence of optical layer 540, diffuse reflectance of optical film 500 from the viewer side is typically less than 10%. In some instances the diffuse reflectance is less than 8%. In still other instances the diffuse reflectance is less than 5%.

Optical layer 540 is preferably a highly light transmissive layer that is preferably conformably coated onto the exposed areas of beads 530 and optically absorptive layer 520 and is intended to improve the overall performance of the optical film 500. Optical layer 540 may be a hardcoat to increase durability of optical film 500. Optical layer 540 may be an anti-reflection coating to increase the overall optical throughput of optical film

500 while at the same time reduce overall reflectance of optical film 500 from the viewer side. In such case, diffuse reflectance of optical film 500 from the viewer side is typically less than 8%. In some instances the diffuse reflectance is less than 4%. In still other instances the diffuse reflectance is less than 2%. Optical layer 540 may also have optical diffusion properties to further control the viewing angle of light exiting the optical film. Optical layer 540 may also include a colorant. Generally, high specular and diffuse reflectance from viewer side reduces a display's contrast. Optical film 500, in accordance with one embodiment of the invention, absorbs a substantial portion of ambient light, thereby having low total (i.e., specular plus diffuse) reflectance, and incorporates a matte surface on its output side, thereby having low specular reflectance. Optical film 500, according to this embodiment of the invention, has low specular and diffuse reflectance, thereby displaying information with high contrast.

Substrate 510 preferably has high optical transmission. The substrate may be clear or diffuse. The substrate itself may diffuse light, for example, by bulk and/or surface diffusion. Surface diffusion may be achieved by making surface 510A matte. Substrate 510 may be flexible or rigid and may have a colorant to optimize the color of light exiting optical film 500 towards viewer 550. Substrate 510 can be any suitable material that is substantially light transmissive. Examples of materials particularly suited as a substrate include polyethylene terapthalate (PET), polycarbonates, acrylics, glass, and other similar substrate materials. The optically absorptive layer 520 typically comprises a mixture of light absorptive material dispersed in a binder. Particularly suitable light absorptive materials include carbon black, light absorptive dyes such as black dyes and other similar light absorptive dyes, and other similar light absorptive materials. Examples of particularly suitable binders include thermoplastics, radiation cured or thermoset acrylates, epoxies, silicone- based materials, pressure sensitive adhesives, and other similar binder materials. Other materials such as dispersants, surfactants, viscosity modifiers, curing agents, and the like can also be included.

Beads 530 can be made of any suitable material that is clear and highly transmissive to light. Examples of particularly suitable materials include various types of glass, polymeric materials including polymethylmethacrylate (PMMA), polystyrene, mixtures of two or more different materials, and other similar bead materials. The beads are preferably substantially spherical, but may have other suitable shapes including oval or other desired shapes. An oval shaped bead 530 may be used to tune viewing angle of light exiting optical film 500 in one or more directions such as horizontal and vertical directions or other directions. The diameter range of beads 530 and the thickness of optically absorptive layer 520 are preferably chosen such that most beads are partially embedded in layer 520 to optimize optical throughput while maintaining high contrast. As the bead diameter is increased the information displayed to the viewer will look more grainy and have less resolution. On the other hand, if the diameter of beads 530 is too small the optical throughput of film 500 can decrease if the overall contrast is to be maintained. Beads 530 typically have an index of refraction that provides a desired optical performance, for example, a desired optical transmittance and/or viewing angle. Beads

530 may have an index of refraction ranging from 1.3 to 3.5, and preferably 1.3 to 2.4. The thickness of the optically absorptive layer may be more than the average bead radius in order to increase durability of optical film 500. Alternatively, the thickness can be less than the average bead radius in order to increase total optical transmittance of optical film 500.

Light source 501 may be a single light source or an array of individual light sources. Light source 501 may be a point light source or an extended light source. Light originating from light source 501 and incident onto beads 530 is preferably diffuse to optimize optical throughput of film 500. Light source 501 may emit light in a collimated or diffuse form. If light source 501 is not sufficiently diffusive substrate 510 may be made sufficiently diffusive. Alternatively, a suitable additional diffuser may be placed between light source 501 and input face 510.

Light source 501 may or may not display an image. Examples of a light source displaying an image include liquid crystal display, light emitting diode display, plasma display, organic light emitting display, field emission display, electroluminiscent display, and other suitable image forming displays. Examples of light sources not displaying an image include light bulb, light emitting diode, and other suitable light sources not displaying an image. If light source 501 displays an image then it is preferable that the viewing angle of a displayed image be large to optimize the optical throughput of film 500 and that the distance between the image plane of light source 501 and beads 530 be small to maintain image quality and resolution. Fig. 7 illustrates a schematic of another embodiment according to the present invention. An optical assembly 900 is positioned between a light source 901 and a viewing position 950. Light is incident onto optical assembly 900 from light source 901 and exits the optical assembly towards viewing position 950. Ambient light is incident onto optical assembly 900 from the viewer side. Optical assembly 900 includes one or more display members 915, a substrate 910, a light absorbing layer 920, a plurality of beads 930, and an optional optical layer 940. Substrate 910 has an input face 910A and an output face 910B. Beads 930 are partially embedded in layer 920 and are preferably in close proximity to face 910B of substrate 910 to optimize overall optical throughput of optical assembly 900.

According to Fig. 7, display member 915 is positioned between light source 901 and input face 910A of substrate 910. Alternatively, display member 915 or an additional display member 915 may be positioned between beads 930 and viewing position 950. Display member 915 includes an optional display layer 905 and display graphics 906. Display layer 905 has an input face 905 A and an output face 905B. Display graphics 906 are formed on surface 905 A and/or surface 905B. Three such display graphics are illustrated in Figs. 8, 9, and 10. Fig. 8 illustrates a frontal schematic of a left arrow indicator 1011 and a right arrow indicator 1012 on background 1013. Fig. 9 illustrates a frontal schematic of alphanumerics 1121 and indicators 1123 on background 1122. Fig. 10 illustrates a frontal schematic of a battery indicator 1231 on background 1232. The graphics shown in Figs. 8, 9, and 10 may be part of a display in an instrument cluster in a motor vehicle, an airplane, a boat, or any other display using display graphics.

Referring back to Fig. 7, display member 915 may be laminated to substrate 910 using an adhesive such as a pressure sensitive adhesive. Alternatively, display member 915 may be bonded to substrate 910 by mechanical means, sonic welding, or other appropriate means. Alternatively, display graphics may be formed on input face 910A of substrate 910. Alternatively, display graphics may be formed onto surfaces of beads 930. Display graphics may be formed by such methods as printing, photolithography, or other appropriate methods. Features on the display graphics may be clear, colored, translucent, or opaque.

Display layer 905 may be flexible or rigid. Display layer 905 may be any suitable material that is substantially light transmissive. Examples of suitable materials include display member 915 may be positioned between beads 930 and viewing position 950. Display member 915 includes an optional display layer 905 and display graphics 906. Display layer 905 has an input face 905 A and an output face 905B. Display graphics 906 are formed on surface 905 A and/or surface 905B. Three such display graphics are illustrated in Figs. 8, 9, and 10. Fig. 8 illustrates a frontal schematic of a left arrow indicator 1011 and a right arrow indicator 1012 on background 1013. Fig. 9 illustrates a frontal schematic of alphanumerics 1121 and indicators 1123 on background 1122. Fig. 10 illustrates a frontal schematic of a battery indicator 1231 on background 1232. The graphics shown in Figs. 8, 9, and 10 may be part of a display in an instrument cluster in a motor vehicle, an airplane, a boat, or any other display using display graphics.

Referring back to Fig. 7, display member 915 may be laminated to substrate 910 using an adhesive such as a pressure sensitive adhesive. Alternatively, display member 915 may be bonded to substrate 910 by mechanical means, sonic welding, or other appropriate means. Alternatively, display graphics may be formed on input face 910A of substrate 910. Alternatively, display graphics may be formed onto surfaces of beads 930. Display graphics may be formed by such methods as printing, photolithography, or other appropriate methods. Features on the display graphics maybe clear, colored, translucent, or opaque.

Display layer 905 may be flexible or rigid. Display layer 905 may be any suitable material that is substantially light transmissive. Examples of suitable materials include polyethylene terapthalate (PET), polycarbonates, acrylics, glass, and other suitable substrate materials.

Optical layer 940 is preferably a highly light transmissive layer that is preferably conformably coated onto the exposed areas of beads 930 and optically absorptive layer 920 and is intended to improve the overall performance of the optical film 900. Optical layer 940 may be a hardcoat to increase durability of optical film 900. Optical layer 940 may be an anti-reflection coating to increase overall optical throughput of optical film 900 while at the same time reduce overall reflectance of optical film 900 from the viewer side. Optical layer 940 may also have optical diffusion properties to further control the viewing angle of light exiting the optical film. Optical layer 940 may also include a colorant. Optical assembly 900 may further include a rotatable pointer 925. Pointer 925 may be part of an instrument cluster such as a tachometer, a fuel gauge, or any other gauge or instrument using a pointer. Pointer 925 includes a pointer arm 926 that can rotate about a pivot 927. Pointer 925 is generally positioned between light source 901 and viewing position 950. According to Fig. 9, pointer 925 is positioned between light source 901 and display member 915. Alternatively, pointer 925 may be positioned on the viewer side of optical assembly 900, between beads 930 and viewing position 950, in which case optical assembly 900 may further include an optically transmissive layer between the pointer and the viewing position to protect the pointer against damage. Pointer 925 may be clear, or translucent, or opaque. Pointer 925 may be illuminated by a light source other than light source 901. An example is disclosed in US Patent 4,9595,759. It can be appreciated that optical assembly 900 displays information and graphics to viewing position 950 with high contrast, low glare, and generally with reduced viewing angle.

While the present invention has been described above with reference to various embodiments, it should not be limited to the specifics of the embodiments. Rather, the intention is to fully cover the invention as defined in the attached claims.

Claims

What is claimed is:

1. An optical system for displaying information, the optical system comprising: a light source; and an optical film having an input side facing said light source and a viewing side, wherein total optical transmittance of said optical film for light incident from said light source on said input side of said optical film and exiting said viewing side of said optical film is greater for diffuse incident light than for collimated incident light.

2. The optical system according to claim 1 wherein light incident on said optical film and originating from said light source is transmitted through said optical film having a viewing angle that is less than a half cone angle of said incident light.

3. The optical system according to claim 1 wherein the viewing angle of light exiting said viewing side of said optical film and originating from said light source is different in horizontal and vertical directions.

4. The optical system according to claim 1 wherein the total optical transmittance of said optical film for diffuse incident light originating from said light source is greater than 20%.

5. The optical system according to claim 1 wherein the total optical transmittance of said optical film for diffuse incident light originating from said light source is greater than 40%.

6. The optical system according to claim 1 wherein a total optical reflectance of said optical film for collimated light incident on said viewing side of said optical film is less than 10%.

7. The optical system according to claim 1 wherein a total optical reflectance of said optical film for collimated light incident on said viewing side of said optical film is less than 5%.

8. The optical system according to claim 1 wherein light incident on said input side of said optical film originating from said light source is diffuse.

9. The optical system according to claim 1 wherein light incident on said input side of said optical film originating from said light source is collimated.

10. An optical system for displaying information to a viewer, the optical system comprising: a light source; and an optical film, having an input side facing said light source and an output side opposite to the input side, disposed between said light source and the viewer, the optical film including, an optically absorptive layer, and a plurality of transparent beads partially embedded in said optically absorptive layer, the embedded portion of said beads being on the input side of said optical film such that a portion of light received by the input side of said optical film from said light source is transmitted through said beads towards the viewer.

11. The optical system of claim 10 wherein said light source is diffuse.

12. The optical system of claim 10 wherein said light source is collimated.

13. The optical system of claim 10 wherein light incident on said optical film originating from said light source is diffuse.

14. The optical system of claim 10 wherein light incident on said optical film originating from said light source is collimated.

15. The optical system of claim 10 wherein said light source displays an image.

16. The optical system of claim 15 wherein said light source comprises a liquid crystal display.

17. The optical system of claim 15 wherein said light source comprises a light emitting display.

18. The optical system of claim 15 wherein said light source comprises an organic light emitting display.

19. The optical system of claim 15 wherein said light source comprises a plasma display.

20. The optical system of claim 10 further comprising an optically transmissive substrate disposed on said input side of said optical film between said optically absorptive layer and said light source.

21. The optical system of claim 20 wherein said substrate has colorant.

22. The optical system of claim 20 wherein said substrate comprises an optical diffuser.

23. The optical system of claim 20 wherein said optically absoφtive layer is coated on said optically transmissive substrate.

24. The optical system of claim 10 wherein said optically absoφtive layer comprises a light absorbing dye or pigment in a binder.

25. The optical system of claim 10 wherein said beads are substantially spherical.

26. The optical system of claim 10 wherein said beads have an asymmetric profile.

27. The optical system of claim 10 wherein said beads are colored.

28. The optical system of claim 10 wherein said beads have an index of refraction ranging from 1.3 to 3.5.

29. The optical system of claim 10 wherein said beads partially protrude through said optically absoφtive layer.

30. The optical system of claim 29 further comprising an optically transmissive substrate disposed on said input side of said optical film between the optically absoφtive layer and the light source.

31. The optical system of claim 10 wherein said beads comprise one or more types of bead each of said type of beads having a different index of refraction.

32. The optical system of claim 10 further comprising a light transmitting layer disposed on at least one of an exposed surface of said beads and a surface of said optically absoφtive layer on the output side of said optical film.

33. The optical system of claim 32 wherein said light transmitting layer comprises a hardcoat.

34. The optical system of claim 32 wherein said light transmitting layer comprises an anti-reflecting layer.

35. The optical system of claim 32 wherein said light transmitting layer comprises a matte finish.

36. The optical system of claim 10 wherein light incident on said optical film and originating from said light source is transmitted through said optical film and exits the output side of said optical film with a viewing angle that is less than a half cone angle of the incident light.

37. The optical system of claim 10 wherein a viewing angle of light exiting the output side of said optical film and originating from said light source is different in horizontal and vertical directions.

38. An optical system for displaying information to a viewer, the optical system comprising: a light source; and an optical film adapted to be disposed between said light source and said viewer, the optical film including, a substrate having an input side for receiving light from said light source and an output side, an optically absoφtive layer, having an input side and an output side, disposed on the output side of said substrate, the input side of said optically absoφtive layer facing the output side of said substrate, and a plurality of beads transmissive to light partially embedded in said optically absoφtive layer leaving a side of said beads exposed on the output side of the optically absoφtive layer, wherein a portion of light incident on the input side of said substrate from said light source is transmitted by said beads through said optical film to be viewed by the viewer.

39. The optical of claim 38 further comprising a display layer having an input face and an output face and display graphics disposed on at least one of said input face and said output face of said display layer, the display layer being adapted to be disposed between the light source and the viewer.

40. The optical system of claim 39 wherein said display layer is optically clear.

41. The optical system of claim 39 wherein said display layer has a thickness from 10 to 500 microns.

42. The optical system of claim 39 wherein one of said display layer and said display graphics is disposed onto said substrate.

43. The optical system of claim 39 wherein one of said display layer and said display graphics is disposed on at least one of an exposed portion of said beads and said optically absoφtive layer.

44. The optical system of claim 39 wherein one of said display layer and said display graphics is laminated to said substrate.

45. The optical system of claim 39 wherein one of said display layer and said display graphics is laminated to at least one of an exposed portion of said beads and said optically absoφtive layer.

46. The optical system of claim 39 wherein one of said display layer and said display graphics is discontinuous.

47. The optical system of claim 39 wherein said display graphics are translucent in predetermined areas.

48. The optical system of claim 39 wherein said display graphics are clear in predetermined areas.

49. The optical system of claim 39 wherein said display graphics are colored in predetermined areas.

50. The optical system of claim 39 wherein said display graphics are opaque in predetermined areas.

51. The optical system of claim 39 wherein said display graphics comprise at least one of alphanumerics, icons, and indicia.

52. The optical system of claim 38 further comprising display graphics adapted to be disposed between said light source and the viewer.

53. The optical system of claim 52 wherein the display graphics are printed onto at least an exposed portion of at least one of said beads and said optically absoφtive layer.

54. The optical system of claim 52 wherein the display graphics are printed on at least one of said input side and said output side of said substrate.

55. The optical system of claim 52 wherein said display graphics are translucent in predetermined areas.

56. The optical system of claim 52 wherein said display graphics are clear in predetermined areas.

57. The optical system of claim 52 wherein said display graphics are colored in predetermined areas.

58. The optical system of claim 52 wherein said display graphics are opaque in predetermined areas.

59. The optical system of claim 52 wherein said display grapliics comprise at least one of alphanumerics, icons, and indicia.

60. The optical system of claim 38 wherein the light absoφtive layer comprises a light absorbing dye or pigment in a binder.

61. The optical system of claim 38 wherein said beads partially protrude said optically absoφtive layer into said substrate.

62. The optical system of claim 38 wherein the beads are substantially spherical.

63. The optical system of claim 38 wherein said beads have asymmetric profile.

64. The optical system of claim 38 wherein the beads have colorant.

65. The optical system of claim 38 wherein the beads have index of refraction ranging

66. The optical system of claim 38 further comprising a light transmitting layer disposed on at least one of an exposed portion of said beads and said optically absoφtive layer.

67. The optical system of claim 66 wherein said light transmitting layer comprises a hardcoat.

68. The optical system of claim 66 wherein said light transmitting layer comprises an anti-reflecting layer.

69. The optical system of claim 66 wherein said light transmitting layer comprises a matte finish.

70. The optical system of claim 38, further comprising a rotatable pointer adapted to be disposed between said light source and said viewing position.

71. The optical system of claim 70 wherein said pointer is disposed between said light source and the input side of said substrate.

72. The optical system of claim 70 wherein said pointer is adapted to be disposed between said beads and the viewer.

73. The optical system of claim 70 wherein said pointer conducts light.

74. The optical system of claim 70 wherein said pointer is translucent.

75. The optical system of claim 70 wherein said pointer is illuminated by a light source other than said light source.

76. A method of displaying an image to a viewer, the method comprising the steps of : providing an optically transmissive substrate having an input side and an output side with an optically absoφtive layer disposed on the output side of said substrate, the optically absoφtive layer having a plurality of beads transmissive to light partially embedded therm such that a portion of the beads are exposed on a side of the optically absoφtive layer opposite the substrate; and illuminating the input side of the substrate with a light source such that a portion of light is transmitted through the substrate and then the beads towards the viewer.

77. The method of claim 76 further comprising the step of disposing a light transmitting layer on at least one of an exposed portion of said beads and said optically absoφtive layer, the light transmitting layer comprising at least one of a hardcoat and an anti- reflecting layer.

78. The method of claim 76 further comprising the step of disposing display graphics between said light source and the viewer.

79. The method of claim 78 further comprising the step of disposing a light transmitting layer on said display graphics.

80. An instrument cluster for displaying information to a viewing position for viewing the intrument cluster, said instrument cluster comprising: a substrate having an input side for receiving light from a light source and an output side facing said viewing position; an optically absoφtive layer having an input side and an output side disposed on said substrate, the input side of said optically absoφtive layer facing the output side of said substrate; and a plurality of beads transmissive to light partially embedded in said optically absoφtive layer leaving a portion of said beads exposed to said viewing position, wherein a portion of light received by the input side of said substrate from said light source is transmitted through said beads towards said viewing position.

81. The instrument cluster according to claim 80 further comprising display graphics disposed between said light source and said viewing position.

82. The instrument cluster according to claim 81 further comprising a light transmitting layer disposed on said display graphics.

83. The instrument cluster according to claim 80 further comprising a light transmitting layer disposed on the exposed portion of said beads and said optically absoφtive layer. '

84. The instrument cluster according to claim 80 wherein said light source is diffuse.

85. The instrument cluster according to claim 80 wherein said light source displays an image.

86. The instrument cluster according to claim 80 wherein light incident on the input side of said optically absoφtive layer and originating from said light source is diffuse.

87. The instrument cluster according to claim 80 further comprising a rotatable pointer disposed between said light source and said viewing position.

88. An instrument cluster according to claim 80 wherein said beads have index of refraction ranging from 1.3 to 3.5.

89. An optical film for use in a display system, the optical film comprising: a substrate having an input side for receiving light from a light source and an output side; an optically absoφtive layer having an input side and an output side disposed on the output side of said substrate, the input side of said optically absoφtive layer facing the output side of said substrate; a plurality of beads transmissive to light partially embedded in said optically absoφtive layer leaving a portion of said beads exposed to a viewing position; and display graphics disposed on at least a portion of at least one of said substrate and said beads, wherein a portion of light received from the input side of said substrate is transmitted tlirough said beads towards said viewing position.

90. The optical film according to claim 89 wherein said display graphics are printed on said beads.

91. The optical film according to claim 89 wherein said display graphics are printed on said substrate.

92. The optical film according to claim 89 wherein said display graphics are laminated to said substrate.