U.S. patent application number 12/168290 was filed with the patent office on 2008-10-30 for optical film having a surface with rounded structures.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Dongwon Chae, Byung-Soo Ko, Leland R. Whitney.
Application Number | 20080266904 12/168290 |
Document ID | / |
Family ID | 36178348 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080266904 |
Kind Code |
A1 |
Ko; Byung-Soo ; et
al. |
October 30, 2008 |
OPTICAL FILM HAVING A SURFACE WITH ROUNDED STRUCTURES
Abstract
The present disclosure is directed to optical devices including
a light source and an optical film having a first surface disposed
to receive light from the light source and a second surface facing
away from the light source. The second surface includes a
two-dimensional array of closely packed substantially
hemispherically-shaped structures. In some implementations of the
present disclosure, the optical film further includes a substrate
portion having an optical characteristic different from optical
characteristics of the second surface comprising the two
dimensional array.
Inventors: |
Ko; Byung-Soo;
(Hwasung-City, KR) ; Whitney; Leland R.; (St.
Paul, MN) ; Chae; Dongwon; (Hwasung-City,
KR) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
36178348 |
Appl. No.: |
12/168290 |
Filed: |
July 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11026940 |
Dec 30, 2004 |
7416309 |
|
|
12168290 |
|
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Current U.S.
Class: |
362/619 |
Current CPC
Class: |
G02B 6/0053 20130101;
G02B 6/0056 20130101 |
Class at
Publication: |
362/619 |
International
Class: |
F21V 8/00 20060101
F21V008/00 |
Claims
1 An optical device, comprising: a light source; a light gating
device; and a gain diffuser exhibiting an optical gain of at least
about 1.2 and comprising a first surface receiving light from the
light source and a second surface facing the light gating device
and comprising a two-dimensional array of closely packed
substantially hemispherically-shaped structures.
2. The optical device of claim 1, wherein the gain diffuser
exhibits an optical gain of at least about 1.4.
3. The optical device of claim 1 further comprising at least one of
a polarizer film, a diffuser film, a brightness enhancing film and
a turning film.
4. The optical device of claim 3, wherein the polarizer film
comprises a diffuse reflective polarizer film.
5. The optical device of claim 1, wherein a refractive index of the
substantially hemispherically-shaped structures is lower than a
refractive index of a layer in the gain diffuser.
6. A direct-lit backlight, comprising: a light source; a light
gating device; and a gain diffuser exhibiting an optical gain of at
least about 1.2 and comprising a first surface facing the light
source and a second surface facing the light gating device and
comprising an array of structures, wherein an output light
intensity distribution of the backlight has a primary, but not a
secondary, peak.
7. The optical device of claim 6, wherein the gain diffuser
exhibits an optical gain of at least about 1.4.
8. The direct-lit backlight of claim 6, wherein the output light
intensity distribution has cylindrical symmetry.
9. The direct-lit backlight of claim 6, wherein the output light
intensity distribution decreases monotonically from the primary
peak.
10. The direct-lit backlight of claim 6, wherein the output light
intensity distribution has a wider viewing angle relative to a
viewing angle of the backlight absent the gain diffuser.
11. The direct-lit backlight of claim 6, wherein the array of
structures comprises an array of substantially
hemispherically-shaped structures.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
11/026,940, filed Dec. 30, 2004, now allowed, the disclosure of
which is incorporated by reference in its entirety herein.
FIELD OF THE INVENTION
[0002] The present disclosure is directed to optical films that
include substantially hemispherically-shaped surface structures and
optical devices incorporating such optical films.
BACKGROUND
[0003] Display devices, such as liquid crystal display ("LCD")
devices, are used in a variety of applications including, for
example, televisions, hand-held devices, digital still cameras,
video cameras, and computer monitors. An LCD offers several
advantages over a traditional cathode ray tube ("CRT") display such
as decreased weight, unit size and power consumption, as well as
increased brightness. However, an LCD panel is not
self-illuminating and, therefore, sometimes requires a backlighting
assembly or a "backlight." A backlight typically couples light from
one or more sources (e.g., a cold cathode fluorescent tube ("CCFT")
or light emitting diode ("LED")) to a substantially planar output.
The substantially planar output is then coupled to the LCD
panel.
[0004] The performance of an LCD is often judged by its brightness.
Brightness of an LCD may be enhanced by using a larger number of
light sources or brighter light sources. In large area displays it
is often necessary to use a direct-lit type LCD backlight to
maintain brightness, because the space available for light sources
grows linearly with the perimeter while the illuminated area grows
as the square of the perimeter. Therefore, LCD televisions
typically use a direct-lit backlight instead of a light-guide
edge-lit type LCD backlight. Additional light sources and/or a
brighter light source may consume more energy, which is counter to
the ability to decrease the power allocation to the display device.
For portable devices this may correlate to decreased battery life.
Also, adding a light source to the display device may increase the
product cost and weight and sometimes can lead to reduced
reliability of the display device.
[0005] Brightness of an LCD may also be enhanced by efficiently
utilizing the light that is available within the LCD device (e.g.,
to direct more of the available light within the display device
along a preferred viewing axis). For example, Vikuiti.TM.
Brightness Enhancement Film ("BEF"), available from 3M Company, has
prismatic surface structures, which redirect some of the light
exiting the backlight outside the viewing range to be substantially
along the viewing axis. At least some of the remaining light is
recycled via multiple reflections of some of the light between BEF
and reflective components of the backlight, such as its back
reflector. This results in optical gain substantially along the
viewing axis and also results in improved spatial uniformity of the
illumination of the LCD. Thus, BEF is advantageous, for example,
because it enhances brightness and improves spatial uniformity. For
a battery powered portable device, this may translate to longer
running times or smaller battery size, and a display that provides
a better viewing experience.
SUMMARY
[0006] In one implementation, the present disclosure is directed to
optical devices including a light source and an optical film having
a first surface disposed to receive light from the light source and
a second surface facing away from the light source, the second
surface including a two-dimensional array of closely packed
substantially hemispherically-shaped structures. In some exemplary
embodiments, the optical film further includes a polarizer.
[0007] In another implementation, the present disclosure is
directed to optical devices including a light source and an optical
film having a first surface disposed to receive light from the
light source and a second surface facing away from the light
source, the second surface including a two-dimensional array with a
first plurality of substantially hemispherically-shaped structures
having a first radius and a second plurality of substantially
hemispherically-shaped structures having a second radius. The
second radius is different from the first radius. The first and
second pluralities of structures are closely packed.
[0008] In yet another implementation, the present disclosure is
directed to optical devices including a light source and an optical
film having a first surface disposed to receive light from the
light source and a second surface facing away from the light
source, the second surface including a two-dimensional array with a
plurality of closely packed substantially hemispherically-shaped
structures having substantially the same radii. In some exemplary
embodiments, the optical film further comprises a substrate portion
having an optical characteristic different from optical
characteristics of the second surface comprising the two
dimensional array.
[0009] These and other aspects of the optical films and optical
devices of the subject invention will become more readily apparent
to those having ordinary skill in the art from the following
detailed description together with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] So that those having ordinary skill in the art to which the
subject invention pertains will more readily understand how to make
and use the subject invention, exemplary embodiments thereof will
be described in detail below with reference to the drawings,
wherein:
[0011] FIG. 1A shows schematically a planar lightguide edge-lit
backlight;
[0012] FIG. 1B shows schematically a wedge lightguide edge-lit
backlight;
[0013] FIG. 1C shows schematically a backlight utilizing an
extended light source;
[0014] FIG. 1D shows schematically a direct-lit backlight;
[0015] FIG. 2 shows schematically an exemplary embodiment of an
optical film according to the present disclosure disposed over a
backlight;
[0016] FIG. 3A is a schematic partial perspective view of an
exemplary optical film constructed according to the present
disclosure;
[0017] FIG. 3B is an iso-candela polar plot for the exemplary
optical film shown in FIG. 3A;
[0018] FIG. 3C contains rectangular distribution plots,
representing cross-sections of the data shown in FIG. 3B taken at
0, 45, 90 and 135 degree angles;
[0019] FIG. 4A is a schematic partial perspective view of another
exemplary optical film constructed according to the present
disclosure;
[0020] FIG. 4B is an iso-candela polar plot for the exemplary
optical film shown in FIG. 4A;
[0021] FIG. 4C contains rectangular distribution plots,
representing cross-sections of the data shown in FIG. 4B taken at
0, 45, 90 and 135 degree angles;
[0022] FIG. 5A is a schematic partial perspective view of another
exemplary optical film constructed according to the present
disclosure;
[0023] FIG. 5B is an iso-candela polar plot for the exemplary
optical film shown in FIG. 5A; and
[0024] FIG. 5C contains rectangular distribution plots,
representing cross-sections of the data shown in FIG. 5B taken at
0, 45, 90 and 135 degree angles.
DETAILED DESCRIPTION
[0025] The present disclosure is directed to optical films capable
of controlling angular distribution of light and optical devices
incorporating such optical films. In particular, the optical films
according to the present disclosure may be capable of controlling
angular output distribution of light from a backlight, such as an
LCD backlight.
[0026] FIGS. 1A-1D show several examples of optical devices, such
as backlights that may be used with LCD panels. FIG. 1A shows a
backlight 2a. The backlight 2a includes a lightguide 3a, which is
illustrated as a substantially planar lightguide, light sources 4a
disposed on one, two or more sides of the lightguide 3a, such as
CCFTs or arrays of LEDs, lamp reflectors 4a' disposed about the
light sources 4a, a back reflector 3a' and one or more optical
films 3a', which may be any suitable optical films. FIG. 1B shows a
backlight 2b including a lightguide 3b, which is illustrated as a
wedge-shaped lightguide, a light source 4b disposed on one side of
the lightguide 3b, such as one or more CCFTs or an array of LEDs, a
lamp reflector 4b' disposed about the light source 4b, a back
reflector 3b' and one or more optical films 3b', which may be any
suitable optical films. FIG. 1C shows a backlight 2c, which
includes an extended light source 4c, which may be a surface
emission-type light source, and one or more optical films 4c'
disposed over the extended light source 4c. FIG. 1D shows
schematically a partial view of a direct-lit backlight 2d, which
includes three or more light sources 4d, such as CCFTs or arrays of
LEDs, a back reflector 5a, a diffuser plate 4d' and one or more
optical films 4d', which may be any suitable optical films.
[0027] Such backlights may be used in various other optical
devices, such as display devices using LCDs (e.g., televisions,
monitors, etc). As one of ordinary skill in the art will
understand, a display device may include a case having a window, a
backlight, which may include at least one light source, a
light-distributing element such as a lightguide, an optical film
according to the present disclosure, other suitable optical films,
and a light-gating device, such as an LCD panel, situated between
the optical film and the optical window and disposed to receive
light transmitted through the optical film. The optical film
according to the present disclosure may be used in conjunction with
any suitable light source known to those of ordinary skill in the
art and the display device may include any other suitable
elements.
[0028] FIG. 2 shows a cross-sectional view of a backlight 20 and an
optical film 6 according to the present disclosure disposed over
the backlight 20 so that a surface 14 (e.g., a first surface) of
the optical film 6 receives light from the backlight. The backlight
20 may include a light source 24, a light distributing element 23
such as a lightguide, and a back reflector 25. The optical film 6
according to the present disclosure has a structured surface 10
(e.g., a second surface) carrying a two-dimensional array of
closely packed substantially hemispherically-shaped structures 8.
In typical embodiments of the present disclosure, the structured
surface 10 faces away from the backlight 20. The optical film 6 may
further include a substrate portion 12. As one of ordinary skill in
the art would understand, the two-dimensional array of closely
packed substantially hemispherically-shaped structures 8 and the
substrate portion 12 may be formed as a single part, and in some
cases from the same material, to produce the optical film 6, or
they may be formed separately and then joined together to produce a
single part, for example, using a suitable adhesive. In some
exemplary embodiments, the array of closely packed substantially
hemispherically-shaped structures 8 may be formed on the substrate
portion 12.
[0029] The two-dimensional array of closely packed substantially
hemispherically-shaped structures 8 of the optical film 6 may be
used to control the direction of light transmitted through the
optical film 6, and, particularly, the angular spread of output
light. The closely packed substantially hemispherically-shaped
structures 8 can be arranged on the surface 10 side-by-side and in
close proximity to one another, and, in some exemplary embodiments,
in substantial contact or immediately adjacent to one another. In
other exemplary embodiments, the substantially
hemispherically-shaped structures 8 may be spaced from each other
provided that the gain of the optical film 6 is at least about 1.1.
For example, the structures 8 may be spaced apart to the extent
that the structures occupy at least about 50% of a given useful
area of the structured surface 10, or, in other exemplary
embodiments, the structures 8 may be spaced further apart to the
extent that the structures occupy no less than about 20% a given
useful area of the structured surface 10.
[0030] Typical exemplary optical films constructed according to the
present disclosure usually are capable of providing optical gain of
at least about 1.1 to at least about 1.5. Some exemplary optical
gain values include about 1.2, 1.4 and 1.5. For the purposes of the
present disclosure, "gain" is defined as the ratio of the axial
output luminance of an optical system with an optical film
constructed according to the present disclosure to the axial output
luminance of the same optical system without such optical film. In
typical embodiments of the present disclosure, the size, shape and
spacing of (or a given useful area covered by) the substantially
hemispherically-shaped structures 8 are selected to provide an
optical gain of at least about 1.1.
[0031] Typically, the optical gain due to the exemplary optical
films having structured surfaces with two-dimensional arrays of
closely packed substantially hemispherically-shaped structures will
decrease as the shape of the rounded structures (such as
protrusions and depressions) departs from hemispherical. Typical
embodiments of the present disclosure include protrusions or
depressions having a height or depth that is within about 60% of
the radius of that structure. More preferably, embodiments of the
present disclosure include protrusions or depressions having a
height or depth that is within about 40% of the radius of that
structure, and most preferably, embodiments of the present
disclosure include protrusions or depressions having a height or
depth that is within about 20% of the radius of that structure.
Such protrusions or depressions having a height or depth that is at
least within about 60% of the radius of that structure will be
referred to as "substantially hemispherical." Larger spacing
between the structures (lesser surface coverage) also can lead to a
decrease in gain.
[0032] Suitable exemplary radii of the substantially
hemispherically-shaped structures 8 include about 5, 8, 10, 12.5,
15, 17.5, 20, 25, 37.5, 45, 50, 60, 70 and 80 microns and the radii
contained in any range between any of these exemplary values. In
some exemplary embodiments, the substantially
hemispherically-shaped structures 8 may be smaller, but not so
small as to cause diffraction effects, or they may be larger, for
example with about 100 or 150 .mu.m radius. Typically, the size of
substantially hemispherically-shaped structures 8 should be small
enough so as not to be readily apparent to a viewer of a display
device containing the optical film. In some exemplary embodiments
that are particularly suitable for use in direct-lit backlights,
the spacing, size, and shape of the substantially
hemispherically-shaped structures 8 can be chosen so that the
optical films of the present disclosure aid in hiding from the
viewer light sources used in the backlight.
[0033] Depending on the desired properties of the optical film 6,
the substantially hemispherically-shaped structures 8 may be
substantially the same shape and/or size or they may be of at least
two or more substantially different shapes and sizes. For example,
an optical film constructed according to the present disclosure can
include substantially hemispherically-shaped structures of a larger
size and substantially hemispherically-shaped structures of a
smaller size disposed between the structures of the larger size so
as to cover a larger portion of the surface 10. In such exemplary
embodiments, a radius of the smaller structure may be about 40% of
the radius of a neighboring larger structure, or it may be another
suitable radius that is small enough for the smaller structures to
be closely packed in a two-dimensional array with the larger
structures. In other exemplary embodiments the substantially
hemispherically-shaped structures 8 may be of at least three
substantially different radii.
[0034] The substantially hemispherically-shaped structures 8, and,
in some embodiments, at least an adjacent part of the substrate
portion 12 including the surface 10, can be made from transparent
curable materials, such as low refractive index or high refractive
index polymeric materials. With high refractive index materials,
higher optical gain may be achieved at the expense of a narrower
viewing angle, while with lower refractive index materials, wider
viewing angles may be achieved at the expense of lower optical
gain. Exemplary suitable high refractive index resins include
ionizing radiation curable resins, such as those disclosed in U.S.
Pat. Nos. 5,254,390 and 4,576,850, the disclosures of which are
incorporated herein by reference to the extent they are consistent
with the present disclosure.
[0035] In some exemplary embodiments, refractive index of the
substantially hemispherically-shaped structures 8 is higher than
that of at least a layer of the substrate portion. Some known
materials suitable for forming the substantially
hemispherically-shaped structures 8 have refractive indices of
about 1.6, 1.65, 1.7 or higher. In other exemplary embodiments, the
substantially hemispherically-shaped structures 8 may be formed
from materials having lower refractive indices, such as acrylic
with the refractive index of about 1.58. In some such exemplary
embodiments, for a polyethylene terephthalate substrate having a
refractive index of about 1.66, a preferred range of refractive
indices of the structures 8 (and, perhaps, an adjacent portion of
the film) is from about 1.55 to about 1.65.
[0036] The substrate portion 12 can have an additional optical
characteristic that is different from the optical characteristics
of the two-dimensional array of closely packed substantially
hemispherically-shaped structures 8, such that the substrate
portion manipulates light in a way that is different from the way
light is manipulated by the two-dimensional array disposed on the
surface 10. Such manipulation may include polarization, diffusion
or additional redirection of light transmitted through the optical
films of the present disclosure. This may be accomplished, for
example, by including in the substrate portion an optical film
having such an additional optical characteristic or constructing
the substrate portion itself to impart such an additional optical
characteristic. Exemplary suitable films having such additional
optical characteristics include, but are not limited to, a
polarizer film, a diffuser film, a brightness enhancing film such
as BEF, a turning film and any combination thereof. Turning film
may be, for example, a reversed prism film (e.g., inverted BEF) or
another structure that redirects light in a manner generally
similar to that of a reversed prism film. In some exemplary
embodiments, the substrate portion 12 may include a linear
reflective polarizer, such as a multilayer reflective polarizer,
e.g., Vikuiti.TM. Dual Brightness Enhancement Film ("DBEF") or a
diffuse reflective polarizer having a continuous phase and a
disperse phase, such as Vikuiti.TM. Diffuse Reflective Polarizer
Film ("DRPF"), both available from 3M Company. Additionally or
alternatively, the substrate portion may include a polycarbonate
layer ("PC"), a poly methyl methacrylate layer ("PMMA"), a
polyethylene terephthalate ("PET") or any other suitable film or
material known to those of ordinary skill in the art. Exemplary
suitable substrate portion thicknesses include about 125 .mu.m for
PET and about 130 .mu.m for PC.
[0037] Some display device applications could benefit from
achieving outputs that are more cylindrically symmetrical, which
would be manifested by a more cylindrically symmetrical iso-candela
plot, and/or from achieving outputs that have a relatively wide
angle of view, which would be manifested by a relatively large half
width at half maximum of a corresponding rectangular distribution
plot. Typical exemplary embodiments of the present disclosure can
have half widths at half maximum of the rectangular distribution
plots that are larger than about 33 degrees, for example from 35
degrees to about 40 degrees or greater.
[0038] Traditionally, diffusers have been used to widen a field of
view of display devices. Unlike most traditional diffusers, the
optical films of the present disclosure do not primarily rely on
scattering incident light or redirect it due to variations in
refractive index within the diffuser's body. Instead, the present
disclosure provides optical films that can cause angular spread of
the incident light due to the geometrical configuration of their
structured surfaces and also provide gain of at least about
1.1.
EXAMPLES
[0039] The present disclosure will be further illustrated with
reference to the following examples representing modeled properties
of some exemplary optical films constructed according to the
present disclosure.
Example 1
[0040] FIG. 3A shows a schematic partial perspective view of an
exemplary modeled optical film 106 according to the present
disclosure. The exemplary optical film 106 includes a substrate
portion 112 and a structured surface 110 carrying a two-dimensional
array of closely packed hemispherically-shaped protrusions 108. In
this exemplary embodiment, the protrusions 108 are immediately
adjacent to each other. Each protrusion of this exemplary
embodiment has a radius of about 25 microns and a refractive index
of about 1.58. The substrate portion was modeled as a substantially
planar film with a refractive index of about 1.66.
[0041] FIG. 3B represents a calculated polar iso-candela
distribution plot for light exiting an optical film having the
structure substantially as shown in FIG. 3A placed over a backlight
with the two-dimensional array of closely packed
hemispherically-shaped protrusions 108 facing away from the light
source. The distribution for all Examples was calculated using the
following model: an extended Lambertian source was used on the
first pass of light through the optical film and the remaining
light was recycled using a Lambertian reflector with a reflectivity
of about 77.4%. As one of ordinary skill in the art will
understand, the iso-candela distribution plots show a three hundred
and sixty degree pattern of detected incident light rays having
passed through the optical film. As it is apparent from FIG. 3B,
the output light distribution of this exemplary embodiment has a
relatively high degree of cylindrical symmetry, and the intensity
decreases relatively monotonically without forming secondary peaks
at high angles.
[0042] FIG. 3C shows rectangular candela distribution plots. As one
of ordinary skill in the art will understand, each curve on the
rectangular distribution plots corresponds to a different
cross-section of the polar plot. For example, the curve designated
as 0 degrees represents the cross-section of the polar plot along
the line passing through the center that connects 0 and 180
degrees, the curve designated as 45 degrees represents the
cross-section of the polar plots along the line passing through the
center that connects 45 and 225 degrees, the curve designated as 90
degrees represents the cross-section of the polar plots along the
line passing through the center that connects 90 and 270 degrees,
and the curve designated as 135 degrees represents the
cross-section of the polar plots along the line passing through the
center that connects 135 and 315 degrees. FIG. 3C also illustrates
a relatively high degree of cylindrical symmetry of the output
light distribution of this exemplary embodiment, as well as
relatively monotonically decreasing intensity without secondary
peaks at high angles. This conclusion is illustrated by relatively
small differences between the rectangular intensity plots for
different angles. The rectangular plots also show appreciable
widths of the curves with the average half width at half maximum of
about 40 degrees, which indicates increased amount of diffusion and
a widened viewing angle. Modeled optical gain for the exemplary
gain diffusers constructed according to FIG. 3A was found to be
about 1.48.
Example 2
[0043] FIG. 4A shows a schematic partial perspective view of an
exemplary optical film 206 constructed according to the present
disclosure. The exemplary optical film 206 includes a substrate
portion 212 and a structured surface 210 carrying a two-dimensional
array of closely packed hemispherically-shaped protrusions 208a and
208b. The two-dimensional array of closely packed
hemispherically-shaped protrusions of this exemplary embodiment
includes larger protrusions 208a having about the same size and
smaller protrusions 208b having about the same size disposed
immediately adjacent to each other, so that the smaller protrusions
208b are located in the areas left void by the larger protrusions
208a. This configuration aids in filling the surface 210 with a
higher density. The larger protrusions 208a were modeled as
hemispheres of about 25 micron radii and each of the smaller
protrusions 208b was dimensioned to fit between and immediately
adjacent to the surrounding larger protrusions 208a and had a
radius of about 10 microns. Each protrusion of this exemplary
embodiment has a refractive index of about 1.58. The substrate
portion was modeled as a substantially planar film with a
refractive index of about 1.66.
[0044] FIG. 4B represents a calculated polar iso-candela
distribution plot for light exiting an optical film having the
structure substantially as shown in FIG. 4A placed over a backlight
with the two-dimensional array of closely packed
hemispherically-shaped protrusions 208a and b facing away from the
light source. As it is apparent from FIG. 4B, the output light
distribution of this exemplary embodiment has a relatively high
degree of cylindrical symmetry, and the intensity decreases
relatively monotonically without forming secondary peaks at high
angles.
[0045] FIG. 4C shows rectangular candela distribution plots
corresponding to different cross-sections of the polar plot at 0,
45, 90 and 135 degrees. FIG. 4C also illustrates a relatively high
degree of cylindrical symmetry of the output light distribution of
this exemplary embodiment, as well as relatively monotonically
decreasing intensity without secondary peaks at high angles. This
conclusion is illustrated by small differences between the
rectangular candela plots for different angles. The rectangular
plots also show appreciable widths of the curves, with the average
half width at half maximum of about 37 degrees, which indicates a
widened viewing angle. Modeled optical gain for the exemplary
optical films constructed according to FIG. 4A was found to be
about 1.50.
Example 3
[0046] FIG. 5A shows a schematic partial perspective view of an
exemplary optical film 306 constructed according to the present
disclosure. The exemplary optical film 306 includes a substrate
portion 312 and a structured surface carrying a two-dimensional
array of closely packed hemispherically-shaped depressions 308. In
this exemplary embodiment, the depressions 308 are immediately
adjacent to each other. Each depression of this exemplary
embodiment has a radius of about 25 microns and is disposed in a
film portion having a refractive index of about 1.58. The substrate
portion was modeled as a substantially planar film with a
refractive index of about 1.66.
[0047] FIG. 5B represents a calculated polar iso-candela
distribution plot for light exiting an optical film having the
structure substantially as shown in FIG. 5A placed over a backlight
with the two-dimensional array of closely packed substantially
hemispherically-shaped depressions 308 facing away from the light
source. As it is apparent from FIG. 5B, the output light
distribution of this exemplary embodiment has a relatively high
degree of cylindrical symmetry, and the intensity decreases
relatively monotonically without forming secondary peaks at high
angles.
[0048] FIG. 5C shows rectangular candela distribution plots
corresponding to different cross-sections of the polar plot at 0,
45, 90 and 135 degrees. FIG. 5C also illustrates a relatively high
degree of cylindrical symmetry of the output light distribution of
this exemplary embodiment, as well as relatively monotonically
decreasing intensity without secondary peaks at high angles. This
conclusion is illustrated by insignificant differences between the
rectangular intensity plots for different angles. The rectangular
plots also show appreciable widths of the curves with the average
half width at half maximum of about 43 degrees, which indicates
increased amount of diffusion and a widened viewing angle. Modeled
optical gain for the exemplary optical films constructed according
to FIG. 5A was found to be about 1.21.
[0049] Exemplary optical films according to the present disclosure
can be made by micro-replication from a tool, spray coating, ink
jet printing or any other method known to those of ordinary skill
in the art.
[0050] Thus, the present disclosure provides optical films that can
be configured to exhibit a specific controllable angular spread of
light on the viewing side and a more cylindrically symmetrical
output distribution of light without loss of transmission. Further,
the optical films of the present disclosure exhibit optical gain.
The amounts of gain and angular spread will depend on the specific
configuration of the surface structures and may be varied to
achieve the performance desired for a particular application. In
addition, the structure of the embodiments of the present
disclosure is such that they can have increased robustness, since
the surface features are rounded.
[0051] Although the optical films and devices of the present
disclosure have been described with reference to specific exemplary
embodiments, those of ordinary skill in the art will readily
appreciate that changes and modifications may be made thereto
without departing from the spirit and scope of the present
disclosure.
* * * * *