Brightness enhancement film with improved view angle
A structural shape on the surface of an optical substrate is such that the brightness of diffuse light departing from the surface of the optical substrate at certain off axis angles is reduced, at the expense of a small reduction in peak brightness measured near the viewing axis. The net result is an overall increase in useful illumination. A cross section of a prism as the structural shape has a curved sidewall or facet. A material with a relatively high index of refraction combined with a prismatic structure having a modified prism geometry improves brightness.
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This application is a continuation of U. S. application Ser. No. 10/065,981, filed on Dec. 6, 2002.
BACKGROUND OF THE INVENTIONThis invention relates to brightness enhancement films and, more specifically to such films having curved facet prism structures and increased prism peak angles and refractive indices.
In backlight computer displays or other systems, optical films are commonly used to direct light. For example, in backlight displays, brightness enhancement films use prismatic structures to direct light along the viewing axis (i.e., an axis normal to the display, or “on axis”). This enhances the brightness of the light viewed by the user of the display and allows the system to use less power to create a desired level of on-axis illumination. Films for turning light can also be used in a wide range of other optical designs, such as for projection displays, traffic signals, and illuminated signs.
Backlight displays and other systems use layers of films stacked and arranged so that the prismatic surfaces thereof are perpendicular to one another and are sandwiched between other optical films known as diffusers. Diffusers have highly irregular surfaces.
The use of current commercial brightness enhancement films causes a sharp cut-off in brightness between about 40 and 50 degrees off-axis. At angles beyond this cut-off there are side-lobes in the angular brightness distribution. These side-lobes can result in a waste of energy because they are outside the desired viewing angle specifications of many liquid crystal display (LCD) devices. The side-lobes are also undesirable in security applications since they allow light to reach unintended viewers.
Thus, there is a continuing and demonstrated need in the prior art for brightness enhancement films which suppress sidelobes in the angular distribution of brightness.
SUMMARY OF THE INVENTIONIn a first embodiment, the invention features a structural shape for the surface of an optical substrate such that the brightness of diffuse light departing from the surface of the optical substrate at certain off axis angles is reduced, at the expense of a small reduction in peak brightness measured near the viewing axis. The net result is an overall increase in useful illumination. Such an optical substrate comprises a surface characterized by a cross section of at least one prism having a curved sidewall or facet.
In a second embodiment, the invention features a combination of a high index of refraction prismatic structure with a modified prism geometry. Brightness performance is met or exceeded, for example in an LCD back light display device, when the index of refraction of the prism structure is increased to a value above the index of refraction of materials commonly used in brightness enhancement films, while the peak angle is allowed to increase beyond 90 degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
In
The optical substrates 110 may be positioned, one above the other, in a crossed configuration wherein the prismatic structures 116 are positioned at an angle with respect to one another (e.g., 90 degrees) as seen in
where z is the perpendicular deviation (or “sag”) in microns of the sidewall or facet 132 of the prisms 116 from a straight reference line 128, originating at a first reference point (b) at a base of the prism and terminating at a second reference point (a) near the peak of the prism (see
Linear segments 124, 126 or other approximations to the polynomial described by Eq. 1 may also be used as seen in
Sample cross sections of the prisms 116, over a width w, are shown is
In a second embodiment, a relatively high index of refraction for the optical substrate 110 in combination with a modified prism geometry yields an enhanced brightness. In particular,
Similarly,
Similarly,
Thus, it can be seen from
The optical substrate 110 may be formed from an optically transparent polymer, an ultraviolet (UV) curable organic or inorganic material (or hybrid thereof). In such an optical substrate 110, an index of refraction of greater than about 1.65 is preferred.
Aside from the use of the optical substrates 110 described above in backlight displays for brightness enhancement, the substrates can be used in a wide variety of other applications as well. Embodiments of the substrates 110 can be used in Fresnel lenses, hybrid glass/plastic lenses, optical disks, diffuser films, holographic substrates or in combination with conventional lenses, prisms or mirrors. Such embodiments could be formed by modulating concentric circles or ellipses having fixed characteristics. The optical substrates can also be used in single or multi-order reflective, transmissive or partially transmissive, devices, whether light absorbing or non light absorbing; prisms, holographic optical elements, or diffraction gratings. The substrates can be used in other applications such as projection displays, illuminated signs, and traffic signals. Another property of the invention is that the curved (or compound angle) facets increase the blurring of the light guide features. This is an advantage since it enhances the visual appearance of the display.
Any references to first, second, etc., or front and back, right and left, top and bottom, upper and lower, and horizontal and vertical or any other phrase relating one variable or quantity to another are, unless noted otherwise, intended for the convenience of the description of the invention, and are not intended to limit the present invention or its components to any one positional or spatial orientation. All dimensions of the components in the attached Figures can vary with a potential design and the intended use of an embodiment without departing from the scope of the invention.
While the invention has been described with reference to several embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims
1. An optical substrate comprising:
- a surface comprising a prism structure characterized by a cross section having a plurality of facets described by linear segments approximating a polynomial, wherein adjacent ones of the linear segments intersect at one side of a centerline of the prism, and
- wherein a peak angle of the prism structure is greater than 100 degrees and less than 105 degrees, and the refractive index of the substrate is between approximately 1.65 and 1.8.
2. The optical substrate as set forth in claim 1, wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, 1, and a pitch, p.
3. The optical substrate as set forth in claim 2, wherein the plurality of prisms include at least a pseudorandom peak angle, α, height, h, length, 1, and pitch, p.
4. The optical substrate as set forth in claim 1, wherein the prism structure is an ultraviolet curable organic or inorganic material.
5. A backlight display device comprising:
- an optical source for generating light;
- a light guide for guiding the light therealong including a reflective device positioned along the light guide for reflecting the light out of the light guide;
- an optical substrate receptive of the light from the reflective device, the optical substrate comprising:
- a surface comprising a prism structure characterized by a cross section having a plurality of facets described by linear segments approximating a polynomial, wherein adjacent ones of the linear segments intersect at one side of a centerline of the prism, and wherein a peak angle of the prism structure is greater than 100 degrees and less than 105 degrees, and the refractive index of the substrate is between approximately 1.65 and 1.8.
6. The backlight display device as set forth in claim 5, wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, 1, and a pitch, p.
7. The backlight display device as set forth in claim 6, wherein the plurality of prisms include at least a pseudorandom peak angle, a, height, h, length, 1, and pitch, p.
8. The backlight display device as set forth in claim 5, wherein the prism structure is an ultraviolet curable organic or inorganic material.
9. A backlight display device comprising:
- an optical source for generating light;
- a light guide for guiding the light therealong including a reflective device positioned along the light guide for reflecting the light out of the light guide;
- an optical substrate receptive of the light from the reflective device, the optical substrate comprising:
- a surface comprising a prism structure characterized by a cross section having a plurality of facets including a first facet oriented at a first angle with respect to the surface of the prism and a second facet oriented at a second angle with respect to the surface of the prism, wherein the first and second facets intersect at one side of a centerline of the prism and the first and second angles are different, and wherein a peak angle of the prism structure is greater than 100 degrees and less than 105 degrees, and the refractive index of the substrate is between approximately 1.65 and 1.8.
10. The backlight display device as set forth in claim 9, wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, 1, and a pitch, p.
11. The backlight display device as set forth in claim 10, wherein the plurality of prisms include at least a pseudorandom peak angle, a, height, h, length, 1, and pitch, p.
12. The backlight display device as set forth in claim 9, wherein the prism structure is an ultraviolet curable organic or inorganic material.
Type: Application
Filed: Oct 23, 2006
Publication Date: Feb 15, 2007
Applicant:
Inventor: Eugene Olczak (Glenville, NY)
Application Number: 11/584,500
International Classification: F21V 7/04 (20060101);