U.S. patent application number 11/282151 was filed with the patent office on 2006-09-28 for enhanced electroluminescent sign.
Invention is credited to Zane A. Coleman, Terence E. Yeo.
Application Number | 20060215958 11/282151 |
Document ID | / |
Family ID | 36407819 |
Filed Date | 2006-09-28 |
United States Patent
Application |
20060215958 |
Kind Code |
A1 |
Yeo; Terence E. ; et
al. |
September 28, 2006 |
Enhanced electroluminescent sign
Abstract
An enhanced electroluminescent sign containing a volumetric,
anisotropic scattering element to control the angular spread of
light from the sign and the spatial luminance uniformity of the
sign. The anisotropic scattering element contains one or more
regions of asymmetrically-shaped light scattering particles. The
angular spread of light leaving a sign from a light emitting source
can be efficiently controlled by using a thin, low cost,
volumetric, anisotropic scattering elements to angularly and
spatially distribute light, permitting the reduction in number of
light sources, a reduction in power requirements, or a more
tailored viewing angle.
Inventors: |
Yeo; Terence E.; (Boston,
MA) ; Coleman; Zane A.; (Chicago, IL) |
Correspondence
Address: |
MINTZ, LEVIN, COHN, FERRIS, GLOVSKY;AND POPEO, P.C.
ONE FINANCIAL CENTER
BOSTON
MA
02111
US
|
Family ID: |
36407819 |
Appl. No.: |
11/282151 |
Filed: |
November 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60628769 |
Nov 17, 2004 |
|
|
|
Current U.S.
Class: |
385/31 ; 385/901;
40/547 |
Current CPC
Class: |
G02B 6/0046 20130101;
G09F 13/0409 20130101; G09F 13/22 20130101; G02B 6/0068 20130101;
G02B 6/0041 20130101; G02B 6/0055 20130101 |
Class at
Publication: |
385/031 ;
040/547; 385/901 |
International
Class: |
G02B 6/26 20060101
G02B006/26 |
Claims
1. An electroluminescent sign comprising: a) at least one light
emitting source; b) a first means for displaying a first set of
images or indicia; c) a light transmitting region comprising a
first anisotropic scattering region comprising a first continuous
phase material of refractive index n.sub.c1 and a first dispersed
phase material of refractive index n.sub.d1 wherein
|n.sub.c1-n.sub.d1|>0.001 and one or more of the first dispersed
phase domains are non-spherical in shape disposed to receive light
from the light emitting source and scatter light to the means for
displaying images or indicia.
2. The electroluminescent sign of claim 1 wherein the anisotropic
light scattering region increases the spatial luminous uniformity
of the light pattern illuminating the means for displaying images
or indicia.
3. The electroluminescent sign of claim 1 wherein the anisotropic
light scattering region increases the spatial color uniformity of
the light pattern illuminating the means for displaying images or
indicia.
4. The electroluminescent sign of claim 2 wherein the spatial
uniformity of the light pattern illuminating the means for
displaying images or indicia is greater than or equal to 70%.
5. The electroluminescent sign of claim 1 wherein the sign emits
anisotropic light radiation.
6. The electroluminescent sign of claim 1 wherein the light source
is selected from the group consisting of fluorescent lamps,
cylindrical cold-cathode fluorescent lamp, flat fluorescent lamp,
light emitting diode, organic light emitting diode, field emissive
lamp, gas discharge lamp, neon lamp, filament lamp, incandescent
lamp, electroluminescent lamp, radiofluorescent lamp; halogen lamp;
incandescent lamp; mercury vapor lamp; sodium vapor lamp; high
pressure sodium lamp; metal halide lamp; tungsten lamp; carbon arc
lamp; electroluminescent lamp; laser; photonic bandgap based light
source; quantum dot based light source;
7. The electroluminescent sign of claim 5 containing more than one
light emitting source with the light emitting sources arranged in
an array.
8. The electroluminescent sign of claim 6 wherein the
cross-sectional profile of the light source is substantially longer
in the x direction than the y direction.
9. The electroluminescent sign of claim 7 wherein the array is a
linear array.
10. The electroluminescent sign of claim 5 further comprising a
reflective element.
11. The electroluminescent sign of claim 1 wherein the disperse
phase domains are gaseous.
12. The electroluminescent sign of claim 4 further comprising a
substantially planar output surface wherein the dispersed phase
domains are arranged substantially parallel to the output
surface.
13. The electroluminescent sign of claim 4 further comprising a
substantially planar output surface wherein the dispersed phase
domains are arranged substantially at an angle .delta. to the
output surface.
14. The electroluminescent sign of claim 1 wherein the
concentration of the dispersed phase domains varies spatially in
the light scattering region.
15. The electroluminescent sign of claim 1 wherein the size or
shape of the dispersed phase domains varies spatially in the light
scattering region.
16. The electroluminescent sign of claim 1 wherein the orientation
of the dispersed phase domains varies spatially in the light
scattering region.
17. The electroluminescent sign of claim 1 wherein the light
transmitting region further comprises substantially spherical
particles.
18. The electroluminescent sign of claim 1 wherein the light
transmitting region further comprises a light re-directing
feature.
19. The electroluminescent sign of claim 18 wherein the light
re-directing feature is a light collimating feature.
20. The electroluminescent sign of claim 19 wherein the light
collimating feature is a linear array of prismatic structures.
21. The electroluminescent sign of claim 19 wherein the light
collimating feature is an array of concave surface relief patterns
on a light transmitting material.
22. The electroluminescent sign of claim 19 wherein the light
collimating feature is a coating containing substantially spherical
beads.
23. The electroluminescent sign of claim 1 wherein the light
transmitting region further comprises a second scattering region
disposed to receive light from the light emitting source and direct
light to the means for displaying images or indicia, comprising a
second continuous phase material of refractive index n.sub.c2 and a
second dispersed phase material of refractive index n.sub.d2
wherein |n.sub.c2-n.sub.d2|>0.001 and one or more of the second
dispersed phase domains are non-spherical in shape.
24. The electroluminescent sign of claim 23 wherein the first light
scattering region is separated from the second light scattering
region by a substantially non-scattering region.
25. The electroluminescent sign of claim 1 containing refractive
materials with one or more refractive indexes selected from a group
consisting of: n.sub.dx1.noteq.n.sub.dy1,
n.sub.dx1.noteq.n.sub.dz1, n.sub.dy1.noteq.n.sub.dz1,
n.sub.cx1.noteq.n.sub.cy1, n.sub.cx1.noteq.n.sub.cz1,
n.sub.cy1.noteq.n.sub.cz1.
26. The electroluminescent sign of claim 1 wherein at least one
light emitting source is disposed to direct light into the light
transmitting region of refractive index n.sub.1 such that the light
transmitting region is capable of supporting multiple total
internal reflections.
27. The electroluminescent sign of claim 26 wherein the first light
scattering region is disposed such that one or more dispersed phase
domains scatters incident light into an angle .theta. such that
.theta. < sin - 1 .function. ( 1 n c ) .times. .times. or
.times. .times. .theta. < sin - 1 .function. ( 1 n t ) .
##EQU2##
28. The electroluminescent sign of claim 1 wherein a first set of
image or indicia is viewable at a first angle .alpha. and further
comprising a second means for displaying a second set of image or
indicia viewable from a second angle .beta. such that
.alpha..noteq..beta..
29. The electroluminescent sign of claim 28 wherein
0.degree..ltoreq.|.alpha.-.beta.|.ltoreq.180.degree..
30. The electroluminescent sign of claim 1 wherein the first means
for displaying a first set of images or indicia is selected from a
group consisting of: transparency, photograph, picture, graphic,
print, painting, light directing channels arranged in the outline
of indicia, reflective indicia, light absorbing indicia, light
transmitting indicia, perforated material outlining an image or
indicia, spatial light modulator, liquid crystal display,
electrophoretic display.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. 119(e) to copending U.S. Provisional Application No.
60/628,769, filed on Nov. 17, 2004, the entire contents of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention generally relates to electroluminescent signs
or other devices capable of displaying images or indicia wherein
light is emitted such that indicia can be visually recognized. The
invention also relates to the components contained within the
electroluminescent signs or devices.
BACKGROUND OF THE INVENTION
[0003] Electroluminescent signs such as neon, traditional
fluorescent backlit signs and channel lettering typically direct
light into large angles in the horizontal and vertical directions.
In many cases, the light does not need to be directed in to certain
angular directions because the sign is not normally viewed from
that direction. For example, most signs are typically viewed in the
horizontal direction with only a slight vertical downward direction
needed. The light that is sent high in the vertical direction
upward is often wasted and causes significant light pollution. This
also increases the running costs of the sign due to the increased
electrical power and brighter bulb requirements.
[0004] Fluorescent light bulb-based electroluminescent signs are
generally rectangular in shape due to the typical long cylindrical
shape of the fluorescent bulbs. These signs typically use white
reflecting light boxes and symmetrically scattering diffusers to
spread the light in all directions. Channel letters often diffuse
light into wide angles in the horizontal and vertical directions
using symmetric light scattering films or plastic. A significant
amount of light is absorbed or directed into unnecessary directions
when using these designs.
[0005] Improvements in solid state light sources such as light
emitting diodes (LEDs) are continuously increasing their efficacy
with their luminous output per electrical watt approaching
fluorescent sources. LEDs are essentially point light sources, as
opposed to the extended light sources of fluorescent bulbs. Thus,
the light from an LED can be controlled more effectively (even when
multiple LEDs are used) with the proper optical films and
materials. Traditional diffusers used with point sources such as
LEDs can exhibit speckle. This is typically avoided by using one or
more symmetric diffusers, thick diffusing films, white scattering
surfaces such as printed white dots or white light box walls.
However, these methods inefficiently scatter the light into large
angles and undesirable directions.
[0006] Current optical films used with electroluminescent signs
include symmetrically diffusing films and prismatic films. For
example, the 3M Diffuser Films 3635-30 and 3635-70 are reflecting
and transmitting diffuser films that transmit 30% and 70% of the
incident light, respectively. The light is diffused symmetrically
forward (transmitting) or backward (reflecting) through scattering
from particles. While some light boxes require a significant amount
of the light to be reflected back toward the white light box, these
designs scatter light inefficiently into regions where the light is
absorbed. The components of the light box, including the white
walls and films, absorb a significant amount of the light that is
scattered throughout the light box multiple times. Alternatively,
more efficient and thinner designs such as edge-lit or
waveguide-based electroluminescent signs are sometimes used. Often
with edge-lit or waveguide designs, white scattering dots are
printed on a waveguide or film coupled to a waveguide. These dots
scatter the light symmetrically, and much of the light is scattered
into directions where it is not needed (such as the vertical
direction in many applications). This results in an inefficient
electroluminescent sign.
[0007] Prismatic films such as 3M's Optical Lighting Film (OLF) and
3M's Brightness Enhancement Film (BEF) are sometimes used to direct
the light in the large angles in one plane back toward the forward
direction. For example, the light from a fluorescent bulb-based
edge-lit sign has printed dots on the back that scatter the light
in symmetrical directions. A diffuser is often added to the top of
the waveguide to blend the non-uniformities of the white dots
together and scatter the light into larger angles in both
directions. BEF film can be placed with the prisms aligned in the
horizontal direction to direct some of the light in the large
angles in the vertical directions toward the forward direction. The
first area of inefficiency is the white dots that scatter a portion
of the light back toward the fluorescent bulb, where it leaves the
waveguide and is absorbed by the bulb or other components.
Secondly, the symmetrically-scattering diffuser scatters the light
into large angles where it is unused and also scatters more light
backward towards the waveguide where some of it is absorbed. The
BEF directs some of the light in one plane, but not all of the
light, towards a more forward direction. All of these components
and films add to the volume and cost of the sign with the BEF film
being expensive to manufacture due to microreplication
techniques.
SUMMARY OF THE INVENTION
[0008] What is needed is an enhanced electroluminescent sign that
efficiently directs light into desired viewing angles that is low
cost, has a reduced volume, and is efficient and uniform.
[0009] The present invention relates to enhanced electroluminescent
signs, e.g., containing a volumetric, anisotropic scattering
elements to control the angular spread of light from the sign. The
light scattering element contains one or more regions of
asymmetrically-shaped light scattering domains. The angular spread
of light leaving a sign from a light emitting source can be
efficiently controlled by using a thin, low cost, volumetric,
anisotropic scattering elements to direct the light in the desired
directions. This can permit the reduction in number of light
sources, a reduction in power requirements, or a more tailored
viewing angle. In one embodiment, the volume of the
electroluminescent sign can also be reduced by eliminating the need
the thicker prismatic films used for increased brightness. The
speckle contrast of a sign can be reduced by using more than one
anisotropic light scattering region. When the diffusing element is
used in combination with a waveguide to extract light, the light is
efficiently coupled out of the waveguide in a thin, planar surface.
This diffusive element can be coupled to a reflecting element such
that the resulting combination is a light reflecting element with a
desired anisotropic light scattering profile that can be used to
create an enhanced electroluminescent sign.
[0010] By using anisotropic light scattering elements, one can more
precisely control the angular spread of light, creating a more
optically efficient electroluminescent sign. Additionally, with the
trend in industry to the use of point light sources such as LEDs,
the problem of increased visible speckle contrast on the sign is an
issue. More than one anisotropic scattering element in the path
within the sign can reduce this effect. When used in combination
with waveguide based signs, the anisotropic light scattering
elements can optically couple light from the waveguide more
efficiently that printed dots or symmetric diffusers. Thus, more
light is directed in the forward direction and horizontal angles.
This can reduce the costs, power requirements, speckle and volume
while providing a designed angular viewing range.
[0011] When used with linear arrays of light sources, the
anisotropic diffusing element increases the spatial luminance
uniformity by spreading light into larger angles in the direction
perpendicular to array while substantially maintaining the angular
spread in the direction parallel to the array. The volume of the
electroluminescent sign can also be reduced by eliminating the need
for thicker prismatic films conventionally used for increased
brightness. The speckle contrast and luminance uniformity of a sign
can be reduced by using more than one light scattering region. When
the anisotropic scattering element is used in combination with a
waveguide to extract light, the light is efficiently coupled out of
the waveguide in a thin, planar surface. This anisotropic
scattering element can be coupled to a reflecting element such that
the resulting combination is a light reflecting element with a
desired anisotropic light scattering profile that can be used to
create an enhanced electroluminescent sign.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view of a prior art
electroluminescent bus-stop sign with a substantially isotropic
light output;
[0013] FIG. 2 is a perspective view of an enhanced
electroluminescent bus stop sign with a substantially anisotropic
light output;
[0014] FIG. 3 is a perspective view of an enhanced
electroluminescent window sign with a substantially anisotropic
light output;
[0015] FIG. 4 is a perspective view of an enhanced
electroluminescent sign using a volumetric, anisotropic scattering
waveguide in combination with a reflector and fluorescent bulb;
[0016] FIG. 5 is a perspective view of an enhanced dual-sided
electroluminescent sign using a volumetric, anisotropic scattering
waveguide in combination with two fluorescent bulbs;
[0017] FIG. 6 is a perspective view of an enhanced
electroluminescent sign using a volumetric, anisotropic scattering
waveguide in combination with a reflector and a linear array of
LEDs;
[0018] FIG. 7 is a perspective view of an enhanced
electroluminescent dual-sided sign using a volumetric, anisotropic
scattering waveguide in combination with two linear arrays of
LEDs;
[0019] FIG. 8 is a perspective view of an enhanced
electroluminescent sign using a volumetric, anisotropic scattering
region in combination with a waveguide, reflector, and fluorescent
bulb;
[0020] FIG. 9 is a perspective view of an enhanced
electroluminescent dual-sided sign using two volumetric,
anisotropic scattering regions in combination with a waveguide and
a linear array of LEDs;
[0021] FIG. 10 is a perspective view of an enhanced
electroluminescent sign using a volumetric, anisotropic scattering
region in combination with a tapered waveguide, reflector, and
fluorescent bulb;
[0022] FIG. 11 is a perspective view of an enhanced
electroluminescent sign using a volumetric, anisotropic scattering
region in combination with fluorescent bulbs in a white light
box;
[0023] FIG. 12 is a schematic cross-sectional view of an enhanced
electroluminescent sign using a volumetric, anisotropic scattering
region in combination with fluorescent bulbs with curved
reflectors;
[0024] FIG. 13 is a perspective view of an enhanced
electroluminescent channel letter sign using a volumetric,
anisotropic scattering region in combination with a reflective
channel letter housing and multiple LEDs;
[0025] FIG. 14 is a perspective view of an enhanced
electroluminescent sign using two volumetric, anisotropically
scattering regions spaced apart by a non-scattering region in
combination with a waveguide and a linear array of LEDs.
[0026] FIG. 15 is a graph of the spatial illuminance distribution
from measurements further detailed in Example 1.
[0027] FIG. 16 is a graph of the angular luminance uniformity from
measurements further detailed in Example 1.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The features and other details of the invention will now be
more particularly described. It will be understood that particular
embodiments described herein are shown by way of illustration and
not as limitations of the invention. The principal features of this
invention can be employed in various embodiments without departing
from the scope of the invention. All parts and percentages are by
weight unless otherwise specified.
Definitions
[0029] For convenience, certain terms used in the specification and
examples are collected here.
[0030] "Electroluminescent sign" is defined herein as the means for
displaying information wherein the legend, message, image or
indicia thereon is formed by or made more apparent by an
electrically excitable source of illumination. This includes
illuminated cards, transparencies, pictures, printed graphics,
fluorescent signs, neon signs, channel letter signs, light box
signs, bus-stop signs, illuminated advertising signs, EL
(electroluminescent) signs, LED signs, edge-lit signs, advertising
displays, liquid crystal displays, electrophoretic displays, point
of purchase displays, directional signs, illuminated pictures, and
other information display signs. Electroluminescent signs can be
self-luminous (emissive), back-illuminated (back-lit), front
illuminated (front-lit), edge-illuminated (edge-lit),
waveguide-illuminated or other configurations wherein light from a
light source is directed through static or dynamic means for
creating images or indicia.
[0031] "Anisotropic scattering" refers to scattering of incident
light into directions such that light has different intensities in
different directions. It can also be referred to as asymmetric
scattering, and can include the forward and backward directions,
horizontal and vertical directions. In general, it refers to
unequal scattered light intensities in two or more directions
within a solid angle of 4 pi steradians.
[0032] "Speckle" includes scintillation or the optical interference
pattern visible on a diffusing element.
[0033] "Speckle Contrast" is defined herein as the ratio of the
standard deviation of the luminance fluctuation to the mean
luminance over the area of interest.
[0034] "Scatter," "Scattering," "Diffuse," and "diffusing" as
defined herein includes redirecting of light by reflection,
refraction or diffraction from particles, domains, surfaces, layers
or regions.
[0035] "Optically coupled" is defined herein as condition wherein
two regions or layers are coupled such that the luminance of light
passing from one region to the other is not substantially reduced
by Fresnel interfacial reflection losses due to differences in
refractive indices between the regions. "Optical coupling" methods
include methods of coupling wherein the two regions coupled
together have similar refractive indices or using an optical
adhesive with a refractive index substantially near or in-between
the regions or layers. Examples of "Optical coupling" include
lamination using an index-matched optical adhesive, coating a
region or layer onto another region or layer, or hot lamination
using applied pressure to join two or more layers or regions that
have substantially close refractive indices. Thermal transferring
is another method that can be used to optically couple two regions
of material.
[0036] A "micro-body", "disperse phase domain," "gaseous void,"
"particle" as referred to herein are substantially small regions of
material or blend of materials. They also include gaseous or void
regions defined by the absence of a solid material. The optical
effects of light reflecting from, absorbing or passing through
these regions may vary and the method of manufacturing these
micro-bodies can effect the resulting material and optical
characteristics. Methods of manufacturing these types of
micro-bodies are known in the art and include, but are not limited
to, dispersing materials in a matrix and extruding the blend into a
film, blending the micro-bodies within an extruder and extruding a
film, injection molding a blend of materials, stretching a blend in
conditions where a region is in the solid state such that a void is
created, photopolymerization and monomer diffusion.
[0037] A "spherical" or "symmetric" disperse phase domain includes
gaseous voids, micro-bodies, or particles that substantially
resemble a sphere. A spherical domain may contain surface
incongruities and irregularities but has a generally circular
cross-section in substantially all directions. A "spheroid" is a
type of ellipsoid wherein two of the three axes are equal. An
"asymmetric" domain is referred to here as an "ellipsoidal" domain
wherein each of the three axis can be a different length.
Typically, ellipsoidal domains resemble squashed or stretched
spheres. "Non-spherical" domains include ellipsoidal domains and
other domains defined by shapes that do not resemble a sphere such
as those that not have constant radii. For example, a non-spherical
particle may have finger-like extensions within one plane
(amoeba-like) and substantially planar in a perpendicular plane.
Also, fibrous domains are also non-spherical disperse phase domains
that may have aspect ratios of 10:1, 100:1 or larger.
[0038] "Light guide" or "waveguide" refers to a region bounded by
the condition that light rays traveling at an angle that is larger
than the critical angle will reflect and remain within the region.
In a light guide, the light will reflect or TIR (totally internally
reflect) if it the angle (.alpha.) does not satisfy the condition
.alpha. < sin - 1 .function. ( n 2 n 1 ) ##EQU1## where n.sub.1
is the refractive index of the medium inside the light guide and
n.sub.2 is the refractive index of the medium outside the light
guide. Typically, n.sub.2 is air with a refractive index of
n.apprxeq.1, however, high and low refractive index materials can
be used to achieve light guide regions. The light guide may
comprise reflective components such as reflective films, aluminized
coatings, surface relief features, and other components that can
re-direct or reflect light. The light guide may also contain
non-scattering regions such as substrates. Light can be incident on
a light guide region from the sides or below and surface relief
features or light scattering domains, phases or elements within the
region can direct light into larger angles such that it totally
internally reflects or into smaller angles such that the light
escapes the light guide. The light guide does not need to be
optically coupled to all of its components to be considered as a
light guide. Light may enter from any face (or interfacial
refractive index boundary) of the waveguide region and may totally
internally reflect from the same or another refractive index
interfacial boundary. A region can be functional as a waveguide for
purposes illustrated herein as long as the thickness is larger than
the wavelength of light of interest. For example, a light guide may
be a 5 micron region with 2 micron.times.3 micron ellipsoidal
dispersed particles or it may be a 3 millimeter diffuser plate with
2.5 micron.times.70 micron dispersed phase particles.
[0039] "Angle of view" (AOV) is a measurement of illumination for
all angles relative to two perpendicular axes in the plane of the
material. Typically, the X axis references the horizontal, axis and
the Y axis references the vertical, axis. The angle of view is
measured by applying a "full-width at half maximum" approach, a
"full-width at one-third maximum" approach, and a "full-width at
one-tenth maximum approach." The AOV at full-width at half maximum
(.alpha.(1/2)) is calculated from sum of the absolute value of the
angles (measured from an orthogonal to the plane of the material)
at which the measured luminance is one-half the maximum luminance
measured and noted. For example, if angles of +35.degree. and
-35.degree. were measured to have one-half of the maximum luminance
in the horizontal direction, the AOV .alpha.(1/2) in the horizontal
direction for the screen would be 70.degree.. The AOV at full-width
at one-third maximum (.beta.(1/3)) and the AOV at full-width at
one-tenth maximum (.chi.( 1/10)) are calculated similarly, except
that they are calculated from the angles at which the luminance is
one-third and one-tenth of the maximum luminance respectively.
[0040] The "asymmetry ratio" or "anisotropy ratio" is the
horizontal AOV .alpha.(1/2) divided by the vertical AOV
.alpha.(1/2), and thus is a measure of the degree of asymmetry
between the horizontal luminance and the vertical luminance of the
diffuser.
[0041] This invention is an enhanced electroluminescent sign
containing a volumetric, anisotropic scattering element to control
the angular spread of light from the sign. The light scattering
element contains one or more regions of asymmetrically-shaped light
scattering domains. The spatially uniformity and angular spread of
light leaving a sign from a light emitting source can be
efficiently controlled by using a thin, low cost, volumetric,
anisotropic light scattering elements to direct the light in the
desired directions. This can permit the reduction in number of
light sources, a reduction in power requirements, or a more
tailored viewing angle. The thickness and volume of the
electroluminescent sign can also be reduced by eliminated the
thicker prismatic films used for increased brightness. The speckle
contrast of a sign can be reduced by using more than one
anisotropic light scattering region. When the diffusing element is
used in combination with a waveguide to extract light, the light is
efficiently coupled out of the waveguide in a thin, planar surface.
This diffusive element can be coupled to a reflecting element such
that the resulting combination is a light reflecting element with a
desired asymmetric light scattering profile that can be used to
create an enhanced electroluminescent sign.
[0042] By using anisotropic light scattering elements, one can more
precisely control the angular spread of light, creating a more
optically efficient electroluminescent sign. Additionally, with the
trend in industry to move toward point light sources such as LEDs,
the visible speckle contrast on the sign can increase and the
demands on the external optical components are higher (such as more
diffusion). This is because of the need to maintain the spatial
uniformity due to the nature of moving from extended sources and
closer to point sources. More than one anisotropic scattering
element in the optical path within the sign can improve the
luminance uniformity and reduce the speckle contrast. When used in
combination with waveguide based signs, the anisotropic light
scattering elements can optically couple light from the waveguide
more efficiently that printed dots or symmetric diffusers. Thus,
more light is directed in the forward direction and horizontal
angles. This can reduce the costs, power requirements, speckle and
volume while providing a designed angular viewing range.
[0043] One embodiment of this invention of an electroluminescent
sign comprises of at least one light emitting source, a first means
for displaying a first set of images or indicia and a light
transmitting region comprising a first anisotropic scattering
region comprising non-spherical dispersed phase domains within a
first continuous phase material of a different refractive index
wherein the scattering region scatters light toward the means for
displaying indicia.
[0044] In a further embodiment of this invention, the anisotropic
light scattering region is contained within a waveguide region. By
using a light guide containing substantially aligned asymmetric
particles, more efficient control of the light scattering can be
achieved. One or more regions containing asymmetric particles may
be used and the particle sizes, shapes, concentration, alignment
may vary spatially. The light scattering regions may be
substantially orthogonal in their axis of alignment. Alternatively,
one or more anisotropic scattering films can be used in combination
with a light guide and a reflector to produce an efficient
electroluminescent sign. The light guides may be manufactured by
extruding, embossing, stamping, or compression molding a light
guide in a suitable light guide material containing asymmetric
particles substantially aligned in one direction. The light
scattering light guide or non-scattering light guide may be used
with one or more light sources, collimating films or isotropic or
anisotropic scattering films to produce a uniform anisotropic
electroluminescent sign with a substantially uniform spatial
luminance. By maintaining more control over the scattering, the
efficiency of the sign is increased. The concentration of the
particles may vary throughout the volume and also the shape of the
particles (thus the anisotropic scattering) may vary spatially,
such as to achieve higher luminance uniformity in the sign.
[0045] The non-spherical particles can be added to the matrix
material during processing or they can be created during
manufacturing. In one embodiment, particles not substantially
asymmetric in shape may be stretched along an axis after coating or
during or after an extruding process such that they become
asymmetric in shape. Other methods for achieving a single region of
non-spherical particles in a region are disclosed in U.S. Pat. No.
5,932,342, the text of which is incorporated herein by reference.
By using multiple layers or multi-region methods such as multiple
film stacks, co-extrusion, optical lamination, optical coupling,
thermal bonding, multiple regions containing light scattering
particles can be combined into a single light scattering element.
The degree of stretching can control the asymmetry and thus achieve
a desired level of anisotropic light scattering. The asymmetric
particles may have a large variation in size depending on the
desired level of anisotropy. Methods including co-extrusion,
laminating, thermally bonding, etc can be used to achieve multiple
regions containing dispersed phases with improved optical
performance. The dispersed phase material may blended with the
continuous phase material in a compounding step, a tumbling mixer,
in a solvent blending process, or within an extruder.
[0046] In one embodiment of the invention, the asymmetric particles
in the anisotropic light scattering element are obtained by
reducing particles in size in the x, y or other directions by
stretching a film after or during extrusion.
[0047] In one embodiment of this invention the disperse domains
have a refractive index n.sub.p1 different from the host matrix
material refractive index n.sub.m1 defined by at least one of
|n.sub.mx1-n.sub.px1|.gtoreq.0.001,|n.sub.my1-n.sub.py1|.gtoreq.0.001,
or |n.sub.mz1-n.sub.pz1|.gtoreq.0.001 to provide sufficient light
scattering. The differential refractive index (.DELTA.n.sub.MP)
defined as the absolute value of the difference between the index
of refraction of the matrix (n.sub.M1) and the index of refraction
of the particles (n.sub.p1), or |n.sub.M1-n.sub.p1|, may be from
about 0.001 to about 0.8, and preferably is from about 0.01 to
about 0.2 in the x, y, or z directions.
[0048] It is recognized that when a film is stretched that contains
solid particles, voids can be created. These can be substantially
linear when the film is stretched along one axis. In this case, the
disperse phase domains are gaseous (or a vacuum) with a
significantly larger refractive index difference between the
disperse phase domains and continuous phase material. This
increases the scattering and can be used to reduce the
concentration (or % volume) of the gaseous phase domains, reduce
the thickness of the region, or otherwise improve the optical
performance.
[0049] When more than one type of non-spherical domains are used
within an anisotropic light scattering region, they may have a
refractive index n.sub.p2 in the x, y, or z direction that is the
same or different to that of the continuous phase or the dispersed
phase refractive index. Alternatively, the matrix phase may have a
different refractive index in the x, y, or z directions
(birefringent or tri-refringent).
[0050] The asymmetric features, e.g. micro-bodies, typically are
all oriented with their major axes substantially in one direction
in the plane of the surface of the material. Desirably, the
particles are made from a material which is capable of being
deformed at a processing temperature in order to create their
non-spherical shape by stretching. The shape may resemble a
non-spherical ellipsoid or shapes that have non-constant radii in
the x, y, or z direction may also be formed. For example, the
domains may appear randomly shaped in one plane (amoeba-like) and
substantially planar in a perpendicular plane. Further, the volume
density of the particle, the average size and shape, and the index
of refraction in the x, y, and z directions may be optimized to
control desired properties of the light scattering region.
[0051] The average dimension of a dispersed domain or particle in
the x, y, or z direction in the matrix may be from about 1 .mu.m to
about 30 .mu.m, preferably from about 2 .mu.m to about 15 .mu.m,
and most preferably from about 2 .mu.m to about 5 .mu.m in the
minor dimension.
[0052] The average dimension of a dispersed domain or particle in
the x, y, or z direction in the matrix may be from about 2 .mu.m to
about 2 cm, preferably from about 5 .mu.m to about 1 cm, and most
preferably from about 10 .mu.m to about 500 .mu.m in the major
dimension.
[0053] Solid dispersed phase domains in particulate form include
suitable materials such as acrylics, polymethylacrylates;
polystyrenes; polyethylenes; polypropylenes; organic acid cellulose
esters such as cellulose acetate butyrates, cellulose acetates, and
cellulose acetate propionates; polycarbonates; or silicones. The
particles may also contain coatings of higher or lower refractive
index materials. In a preferred embodiment, polyethylene may be
used.
[0054] Other suitable materials for the transmissive micro-bodies
include those that are not deformed during the extrusion or
manufacturing process. These include spherical or non-spherical
materials that have fibrous, plate-like or other orientable shapes.
These include inorganic fibrous material, glass fibers, mica,
silica, cross-linked polymers, plate-like materials, fibrous
polymer materials with high melting points or high glass transition
temperatures. The micro-bodies may be aligned during the
manufacturing process, such as alignment due to stretching or
extruding the region containing the dispersed micro-bodies.
[0055] The light transmitting region of the electroluminescent sign
may also contain a light re-directing feature to re-direct a
portion of the light into specific angular ranges. Typically, these
are surface relief structures on one or more surfaces of the
material. An asymmetric surface relief structure can be
manufactured by techniques as described above, e.g., embossing. The
surface relief desirably contains asymmetrically-shaped features
predominantly aligned in the horizontal or vertical directions such
that they refract, diffract, scatter, diffuse the incident light in
the horizontal or vertical directions.
[0056] The surface relief structure of the light transmitting
region may help reflect, diffract, refract, or scatter light into a
light guide. Alternatively, the surface relief structure of the
light guide may collimate light (bring light at high angles toward
smaller angles towards the normal to the exit face of the sign or
display, for example).
[0057] By using a vertically-oriented prismatic array as the
surface relief structure a significant amount of light can be
directed into angles closer to the sign normal (more collimated).
In one embodiment, the asymmetric micro-bodies are oriented
horizontally (i.e., perpendicular to the prisms) so the scattering
is substantially in the vertical direction (i.e., parallel to the
prisms).
[0058] The alignment of the asymmetric micro-bodies can also vary.
By aligning the particles with respect to the prismatic structure
at angles other than parallel or perpendicular, other anisotropic
light output profiles can be achieved. The asymmetric micro-bodies
will inevitably cause some scattering in the minor axis. This may
be designed to be very small, or significant in order to achieve a
desired angular light output or luminance uniformity. In one
embodiment, the scattering in the minor axis is chosen to be just
sufficient to diffuse the specular component of the light source in
the plane perpendicular to major axis of the prismatic
structure.
[0059] Multiple-element light scattering components within the
electroluminescent sign in accordance with the invention are
desirably optically coupled to one another, i.e., so the luminance
of light passing from one region to the other is not substantially
reduced due to Fresnel interfacial reflection losses due to
differences in refractive indices between the regions. Optical
coupling methods includes, but is not limited to, joining two
regions having similar refractive indices, or by using an optical
adhesive with a refractive index substantially near or in-between
the elements or layers.
[0060] Particles that are significantly smaller than the wavelength
of light may be added to alter the effective refractive index of
the continuous or disperse phase domains. In one embodiment, the
size of the particles are less than 1/10.sup.th the wavelength of
light. In a preferred embodiment, the size of the particles are
less than 1/20.sup.th the wavelength of light of interest such that
significant additional scattering (forward or backward) does not
take place. These particles may be symmetric, asymmetric, or random
in shape. For example, very fine particles of titanium dioxide may
be added to a material to increase the effective refractive index
of the material. The effective refractive index change can adjust
the scattering properties of the material, refractive properties,
and the interfacial reflections.
[0061] The diffusers or light scattering elements of the invention
may also include an optional hardcoat to increase the scratch
resistance of the element, and/or an optional anti-reflective
coating. The hardcoat may be any light-transmissive support layer,
such as a siloxane-based polymer layer. Anti-blocking, UV
absorbing, anti-static and other coatings suitable for use with
optical films or materials used in electroluminescent signs may
also be used.
[0062] FIG. 1 is a perspective view of a typical prior art
electroluminescent sign used at a bus stop. The light from the
back-illuminated sign passes through a graphic displaying the text
"SALE." The light exiting the sign is directed in the +z direction
with a range of angles in the +x, -x, +y, and -y directions. A
significant amount of light traveling in the +y direction is wasted
because the light is not normally seen from that direction.
Likewise, a significant amount of light directed in the -y
direction where it can not be seen.
[0063] FIG. 2 is a perspective view of an enhanced
electroluminescent sign used at a bus stop. The light from the back
illuminated sign exits the sign predominantly in the +x and -x
directions with significantly less light in the +y and -y
directions. This anisotropic light scattering is achieved by using
a volumetric diffusing element with asymmetrically-shaped
particles. The asymmetrically-shaped particles substantially
scatter light in one direction (x direction) more than another (y
direction).
[0064] FIG. 3 is a perspective view of a further embodiment of an
enhanced electroluminescent sign used as an "OPEN" sign. The light
from the sign is predominantly directed in the +z, and x
directions. These types of signs are typically placed at eye level
and thus very little light needs to be directed into the +y and -y
directions. While some light is scattered in the y directions to
accommodate for different viewer heights for example, most of the
light can be directed into the x directions. This is often
quantified by measuring the Full-Width-at-Half-Maximum (FWHM) of
the light luminance versus angle curve for a specific location. In
the embodiment as described in FIG. 3, the FWHM as measured in the
x direction will be larger than the FWHM in the y direction.
[0065] FIG. 4 is a perspective view of another embodiment of an
enhanced electroluminescent sign utilizing a light scattering
waveguide. The waveguide of the sign is a volumetric, anisotropic
scattering element that scatters light out of one of its faces
toward a sign graphic such as a colored transparency. The
asymmetric particles in the volumetric, anisotropic scattering
waveguide are oriented in the y direction and are parallel to the
linear fluorescent bulb. Light scattering from the asymmetric
particles are substantially directed in the x and z directions. The
light that is scattered in the -z direction reflects off of the
reflector the +z direction and can escape the waveguide. A portion
of the light that is scattered in the +z direction will directly be
coupled out of the waveguide toward the sign graphic. The
volumetric diffuse waveguide has a low level of backscatter,
resulting in less light directed back toward the bulb where it can
be lost. There is less scatter in the y direction due to the
asymmetry in the particles. Thus, light is not scattered toward the
sides where it could escape or be directed back into the waveguide
at an angle that could ultimately cause the light to be directed
back toward the source and be absorbed. Since the light bulb is a
substantially linear source aligned in the y direction, one does
not need to scatter as much light in the y direction. Light
scattered in the y direction would not be used efficiently in many
sign applications. More than one light source at one or more edges
may also be used. One or more of the sides or light sources may
utilize a reflector to increase efficiency. Typically, an air gap
is located between the waveguide and the sign graphic such that the
light satisfying the waveguide condition is not unnecessarily
absorbed. Other light scattering (symmetric or asymmetric) or
refracting elements may be optically coupled to or positioned near
the exit surface to provide additional directing or scattering of
the light. The concentration of the light scattering particles can
vary volumetrically or spatially in a plane in order to create a
more uniform output luminance distribution.
[0066] FIG. 5 is a perspective view of an embodiment of an enhanced
electroluminescent sign viewable from opposite sides utilizing an
anisotropic light scattering waveguide. The sign emits light from
two opposite faces of a volumetric, anisotropic scattering
waveguide before passing through the two sign graphics. The
asymmetric particles in the volumetric, asymmetrically diffusing
waveguide are oriented in the y direction and are parallel to the
two linear fluorescent bulbs. Light scattering from the asymmetric
particles will be substantially directed in the x and z directions
out of the waveguide if the waveguide condition is not met.
[0067] FIG. 6 is a perspective view of an enhanced
electroluminescent sign utilizing LEDs as the light source. A
volumetric, anisotropic scattering waveguide is optically coupled
to a reflector. The asymmetric particles in the scattering region
are oriented in the y direction and the linear array of LEDs is
aligned in the y direction. The light from the LEDs is coupled into
the waveguide through one edge. Light from the LEDs is reflected by
the reflector and totally internally reflects within the light
scattering region when the waveguide condition is satisfied. A
portion of the light that is scattered from the asymmetric
particles is coupled out of the waveguide and through the air gap
and sign graphic into the +z and x directions. The light that is
scattered in the -z direction will reflect off of the reflector and
be directed in the +z direction. A portion of the light that is
scattered in the +z direction will directly be coupled out of the
waveguide if the waveguide condition is not satisfied. The
volumetric light scattering region has low level of backscatter,
thus less light is directed toward back toward the light source
where it may be absorbed. There is less scatter in the y direction
due to the asymmetry in the particles. As a result, less light is
scattered toward the edges where it could escape or be directed
back into the waveguide at an angle that could ultimately cause the
light to be directed back toward the source and be absorbed. More
than one array of LEDs may be used in two or more edges. Single LED
sources may also be used depending on the desired brightness and
size of the sign. Arrays of light sources other than LEDs may be
used. More than one array of light sources may be utilized to
increase the brightness or uniformity. The arrays may be of
predominantly one color (white for example) or they may be of
multiple colors (red, green, and blue for example). In the cases
where the LED's are not of the same color, increased color
uniformity may be achieved by the use of one or more anisotropic
light scattering regions. In a one embodiment of this invention, an
anisotropic light scattering region is disposed in a light
transmitting region located between one or more of the light
sources and an input surface of a region capable of supporting a
waveguide. The anisotropic region scatters light from the different
colored sources such that the perceived color is the summation of
the diffuse contributions from the sources. One or more of the
sides and light sources may utilize a reflector to increase
efficiency. Other scattering (symmetric or asymmetric) or
refracting elements may be optically coupled to or positioned near
the entrance or exit surface to provide additional directing or
scattering of the light. Reflective components including reflective
films and reflectors can be positioned around the light sources, or
at one of the surfaces or edges.
[0068] FIG. 7 is a perspective view of further embodiment of an
enhanced electroluminescent sign visible from opposite sides
utilizing two linear arrays of LEDs and a volumetric, anisotropic
scattering waveguide. The asymmetric particles in the scattering
region are oriented in the y direction and the linear array of LEDs
is aligned in the y direction. The light from the LED arrays is
coupled into the waveguide through the edges. Light from the LEDs
is totally internally reflected within the light scattering region
when the waveguide condition is satisfied. A portion of the light
that is scattered from the asymmetric particles is coupled out of
the waveguide and through the air gap and sign graphic into the z
and x directions. A portion of the light that is scattered in the z
direction will directly be coupled out of the waveguide if the
waveguide condition is not satisfied. The volumetric light
scattering region has low level of backscatter, thus less light is
directed toward back toward the light source where it may be
absorbed. There is less scatter in the y direction due to the
asymmetry in the particles. As a result, less light is scattered
toward the sides where it could escape or be directed back into the
waveguide at an angle that could ultimately cause the light to be
directed back toward the source and be absorbed. By using two
linear LED arrays, a compact, high brightness electroluminescent
sign efficiently scatters the light in the x and z directions. The
sign can be thinner than signs using prismatic films before the
sign graphic to reduce the angles of diffusion along one axis.
Single LED sources may also be used depending on the desired
brightness and size of the sign. Arrays of light sources other than
LEDs may be used. One or more of the sides and light sources may
utilize a reflector to increase efficiency. Other scattering
(symmetric or asymmetric) or refracting elements may be optically
coupled to or positioned near the entrance, edges, or exit surface
to provide additional directing or scattering of the light. The
sign graphics may be designed to reflect light back into the
waveguide in the regions corresponding to the darker areas of the
graphic to improve light efficiency.
[0069] FIG. 8 is a perspective view of another embodiment of an
enhanced electroluminescent sign wherein a volumetric,
asymmetrically scattering region is optically coupled to a
waveguide and a reflector in a sign. A sign graphic is spaced from
the waveguide by an air gap. The asymmetric particles in the
scattering region are oriented in the y direction. A thin,
asymmetric diffuser coupled to a reflector allows the use of
traditional transparent substrates for the waveguide and can reduce
costs. The light from the fluorescent bulb is coupled into the
waveguide through one edge. Light from the fluorescent bulb is
reflected by the reflector and totally internally reflects within
the waveguide when the waveguide condition is satisfied. Light that
is scattered from the asymmetric particles can be coupled out of
the waveguide into the +z and x directions. The light that is
scattered in the -z direction can reflect off of the reflector back
into the +z direction where it can be scattered again, escape the
waveguide, or reflect off a reflector or other surface if the
waveguide condition is satisfied. A portion of the light that is
scattered in the +z direction will directly be coupled out of the
waveguide. The light traveling in the y direction, or with some
component thereof, that is coupled into the waveguide and exits the
waveguide is not substantially scattered further by the particles
in the y direction such that the angular spread of light in the y
direction is increased.
[0070] FIG. 9 is a perspective view of further embodiment of an
enhanced electroluminescent sign viewable from opposite sides
wherein two volumetric, anisotropic scattering regions are
optically coupled to a waveguide. By using two volumetric,
anisotropic scattering elements spaced apart by the waveguide, the
uniformity of the light scattering out of the sign is increased and
the speckle contrast is reduced. The sign graphics are spaced from
the waveguide by air gaps in order to maintain a waveguide. The
asymmetric particles in the scattering regions are oriented in the
y direction. Thin, anisotropic diffusers coupled to the waveguide
scatter light efficiently out of the waveguide and through the sign
graphics. The light from the linear array of LEDs is coupled into
the waveguide through one edge. One or more anisotropic light
scattering diffuser may be used in front of the linear array of
LEDs or coupled to the edge of the waveguide in order to make
spatial luminance of the light entering the waveguide more uniform
in the y direction. Light from the LEDs totally internally reflects
within the waveguide when the waveguide condition is satisfied.
Light that is scattered from the asymmetric particles can be
coupled out of the waveguide into the z and x directions. A portion
of the light that is scattered in the z direction will directly be
coupled out of the waveguide. The two volumetric, anisotropic
scattering elements can also be used on opposite sides of a
waveguide for a sign viewable on one side by using a reflector on
one side.
[0071] FIG. 10 illustrates a perspective view of another embodiment
of an enhanced electroluminescent sign wherein a volumetric,
asymmetrically scattering region is optically coupled to a tapered
waveguide and a reflector. The asymmetric particles in the
scattering region are oriented in the y direction. The light from
the fluorescent bulb is coupled into the waveguide through one
edge. Light from the fluorescent bulb is reflected by the reflector
and totally internally reflects within the waveguide when the
waveguide condition is satisfied. By using a tapered waveguide,
more of the light can escape in the regions further from the
fluorescent bulb. Light that is scattered from the asymmetric
particles can be coupled out of the waveguide into the +z and x
directions passing through an air gap and a sign graphic before
reaching a viewer. The light that is scattered in the -z direction
can reflect off of the reflector back into the +z direction where
it can be scattered again, escape the waveguide, or reflect off a
reflector or other surface if the waveguide condition is satisfied.
A portion of the light that is scattered in the +z direction will
directly be coupled out of the waveguide and pass through the sign
graphic.
[0072] FIG. 11 is a perspective view of an embodiment of an
enhanced electroluminescent sign wherein a volumetric, anisotropic
scattering region is located between linear fluorescent bulbs and a
sign graphic. The electroluminescent sign illustrated in FIG. 11
may be scaled to that shown in FIG. 2. The fluorescent bulbs are
located in a white light scattering light box. The asymmetric
particles in the scattering region are oriented in the y direction.
Light reaching these particles is scattered into the +z and x
directions passing through an air gap and a sign graphic before
reaching a viewer. The light from the fluorescent bulbs that
directly reaches the light box region is reflectively scattered in
all directions. This light escapes the light box and travels
through the sign in large angles in the horizontal and vertical
directions. The uniformity and spread of the light from the light
box is increased the horizontal direction by the anisotropic
scattering region. The light from the fluorescent bulbs that
directly reaches the light scattering region is spread in the
horizontal direction to improve the light uniformity in the
horizontal direction. Additional isotropic or anisotropic light
scattering elements may be used between the first light scattering
element and the output surface of the sign. With parallel
fluorescent bulbs, often linear "hot spots" are seen through
traditional signs. With this enhanced sign, some of the light
corresponding to "hot spots" of the bulbs is directed to larger
angles in the horizontal direction so the sign has a more uniform
luminance and reduced visibility of "hot spots." The light in these
hot spot regions is substantially spread into high angles in the
x-z plane. If a second light scattering element is utilized, the
spatial uniformity of the sign is increased significantly without
less scattering in the y-z plane. A reflective light box using
walls made of a reflector such as aluminized Mylar from DuPont and
volumetric anisotropic diffusers may also be used to increase the
uniformity of the light profile and reduce speckle. The
concentration (percent of volume) of the particles may vary
spatially within the volume of waveguide or a thin film. In the
example shown in FIG. 1, the regions of the light scattering region
corresponding to the region directly in front of the fluorescent
bulbs could contain a higher concentration of particles. In this
configuration, more light from the linear "hot spots" may be
directed into larger angles and the uniformity may be increased. An
additional light scattering region would also improve the spatial
luminance uniformity and the concentration of dispersed domains may
be uniform or vary spatially.
[0073] FIG. 12 is a schematic cross-sectional side view of an
enhanced electroluminescent sign utilizing fluorescent bulbs and
reflectors and a volumetric anisotropic diffuser. The reflectors
are positioned behind the bulbs such that the light is collected
and reflected toward the anisotropic diffuser and sign graphic. The
asymmetric particles in the diffuser are aligned in the y
direction. Direct light and light from the reflectors is scattered
in the +z and x directions. The asymmetric diffuser efficiently
scatters light in the x direction. The diffuser may be aligned
horizontal such that the sign scatters most of the light in the
horizontal direction with substantially less scattering in the
vertical direction. The asymmetric diffuser will also reduce the
appearance of the "hot spots" or bright lines directly in front of
the linear fluorescent bulbs by scattering the light strongly in
the x direction. Volumetric asymmetric diffusers may also be
laminated or in close contact with the reflectors to increase the
uniformity of the light profile and reduce speckle. Additional
isotropic or anisotropic light scattering diffusers or refractive
elements may be disposed between the light source and the output
surface of the electroluminescent sign. These light scattering
elements may be separated by thick or thin non-scattering regions
to improve the luminance uniformity and reduce speckle contrast.
The non-scattering regions may be a material or they may be air
gaps.
[0074] FIG. 13 is a perspective view of an embodiment of an
enhanced electroluminescent sign in the form of channel letters
wherein a volumetric, anisotropic scattering region is optically
coupled to a channel letter using LEDs. Channel letters are
typically applied on elevated regions of buildings and the light is
typically scattered in all directions including upwards. By using a
volumetric, asymmetric light scattering region between the light
source and the exit face of the channel letter, the light can be
efficiently spread into large angles in the x direction
(horizontal) and smaller angles in the y direction (vertical).
Other light sources such as neon, fluorescent, incandescent lamps
may be used as the light source. The channel typically reflects the
light from the light source. Additional light reflecting regions or
films may be used in combination or within the anisotropic diffuser
to increase the luminance uniformity of the channel letter. For
example, an additional symmetric or asymmetric diffuser may be used
in the channel letter to increase the angular spread of light and
create the appearance of an extended source. This diffuser may be
located on the walls or back surface of the channel letter or in
front of or behind an anisotropic diffuser. Light reflecting (or
scattering) particles such as titania may be added to the
asymmetric diffuser to reflect some of the light back into the
channel region.
[0075] FIG. 14 is a perspective view of another embodiment of an
enhanced electroluminescent sign wherein multiple volumetric,
anisotropic scattering regions are optically coupled to a waveguide
in a sign. A sign graphic is spaced from the waveguide by an air
gap. The asymmetric particles in the scattering regions are
oriented in the y direction. By using a diffuser containing
multiple regions of asymmetric particles optically coupled to the
waveguide, the control of the angular spread of light is maintained
while the speckle contrast is reduce. The light from a linear array
of LEDs is coupled into the waveguide through one edge. Light from
the LEDs is reflected by the reflector and totally internally
reflects within the waveguide region (composed of the waveguide and
the light scattering regions) when the waveguide condition is
satisfied. Light that is scattered from the asymmetric particles
can be coupled out of the waveguide into the +z and x directions.
The light that is scattered in the -z direction can reflect off of
the reflector back into the +z direction where it can be scattered
again, escape the waveguide region, or reflect off a reflector or
other surface if the waveguide condition is satisfied. A portion of
the light that is scattered in the +z direction will directly be
coupled out of the waveguide. The light that escapes the waveguide
region passes through the sign graphic into an anisotropic pattern
with a larger FWHM of angular luminance in the x direction than in
the y direction.
[0076] The signs or elements of the signs described herein can
contain additional particles or materials to protect (hardcoats),
reduce glare, symmetrically diffuse light (symmetric particles),
and provide other protective or optical enhancement such as those
known to those in the sign design field. The volumetric,
anisotropic diffusers may be made using flexible or rigid materials
and may be used with existing signs or combined in a sign package
or device. The anisotropic diffusers may be shaped, cut into
patterns such as to provide a patterned spatial light
luminance.
[0077] The different variations in features and designs of the
enhanced electroluminescent sign described herein can be envisioned
and include, but are not limited to, one or more combinations of
the features described below: [0078] 1. Sign type: back-lighted;
front-lighted; edge-lighted; shaped light-emitting sign; building
mounted; free-standing; interior; externally illuminated;
internally illuminated; channel letter; copy board; electronic
message center; LED sign; wall sign; fascia sign; awning;
projecting sign; sign band; roof sign; parapet sign; window sign;
canopy sign; pylon sign; joint tenant sign; monument sign; pole
sign; high-rise pole sign; directional sign; regulatory sign; mall
sign; point-of-purchase sign; low-profile sign; marquee sign;
backlit awning; readerboard sign; banner sign; hanging sign; device
for displaying information of a legend, message, or indicia
thereon; [0079] 2. Sign graphic type: transparency; printed vinyl;
translucent polymer; glass; shaped light emitting indicia; [0080]
3. Sign graphic location: one face; more than one face; along an
edge; along at least a portion of one surface; [0081] 4. Waveguide
type: none; scattering; non-scattering; polymer; glass; colorless;
tinted; dyed; curved; planar; parallel faces; non-parallel faces;
tapered; [0082] 5. Number of scattering regions: one; two; more
than two; [0083] 6. Scattering region: [0084] a. Scattering region
location: within the waveguide; within a substrate; within a
multi-region diffuser; between the reflective element and the
waveguide; within a coating on a waveguide; within a film optically
coupled to the waveguide; within an adhesive between two elements
of an electroluminescent sign; between a light source and the
waveguide; in the optical path between a light source and a the
sign output surface; [0085] b. Scattering region thickness: greater
than 5 microns and less than 300 mm; [0086] c. Dispersed domain
shape: symmetric; or asymmetric; spherical; non-spherical; or a
combination of both; varying through the volume; varying in a
pattern; random; [0087] d. Dispsersed domain size: between 1 .mu.m
and 30 .mu.m in the minor axis; between 2 .mu.m and 2 cm in the
major axis; varying through the volume; varying in a pattern;
random; small domain size distribution; large domain size
distribution; [0088] e. Light scattering domain refractive index:
average refractive index n.sub.p wherein
|n.sub.p-n.sub.m|>0.001; refractive index n.sub.px and n.sub.py,
in the x and y directions respectively, wherein
|n.sub.px-n.sub.m|>0.001; |n.sub.py-n.sub.m|>0.001; or
|n.sub.py-n.sub.m|>0.001 and |n.sub.px-n.sub.m|>0.001. [0089]
f. Light scattering domain concentration: constant; varying
throughout the volume; regularly varying; random; [0090] g.
Separation between individual scattering regions: greater 5 microns
and less than 300 mm. [0091] h. Asymmetric domain alignment: x
direction; y direction; z direction; at an angle relative to the x,
y, or z directions; static; adjustable; automatically aligned;
varying spatially; [0092] 7. Reflector type: none; metallized
coating; multi-layer reflective plastic; [0093] 8. Light source
type: Fluorescent; cold-cathode fluorescent; compact fluorescent;
neon; radiofluorescent; halogen; incandescent; Mercury vapor;
sodium vapor; high pressure sodium; metal halide; tungsten; carbon
arc; electroluminescent; LED; OLED; laser; photonic bandgap based
light source; quantum dot based light source; [0094] 9. Number of
light sources: one; two; more than two; [0095] 10. Individual light
source color: primary color; non-primary color; white; cool white;
warm white; [0096] 11. Light source optics: none, collimating lens;
collimating reflector; integrator; refractive lens; reflective
lens; anisotropic refracting or scattering element to increase
uniformity; [0097] 12. Waveguide material: none; polymer; rubber;
plastic; glass; [0098] 13. Waveguide extraction method:
symmetrically diffusing regions; asymmetrically diffusing regions;
printed dots; prismatic shapes; surface relief profile; [0099] 14.
Light re-directing feature: collimating; directing; scattering;
refractive; reflective; diffractive; scattering; hybrid; off-axis;
on-axis; bead shaped; hemispherical shaped; non-hemispherical;
prismatic; linear array of prisms; [0100] 15. Prismatic shapes:
none; regular array in x direction; regular array in the y
direction; regular array in the x and y directions; irregular
array; apex angle greater than 90 degrees; apex angle less than 90
degrees; [0101] 16. Bulb or tinted region color: none, primary
color; non-primary color; [0102] 17. Tint location: none; within
substrate; within light scattering region(s); within a
non-scattering region; a separate film or region; [0103] 18.
Diffuser substrate type: none; rigid; flexible; substantially
transparent; substantially opaque; [0104] 19. Substrate location:
none; behind the reflector; in-between the light scattering
regions; in front of the light scattering regions; [0105] 20.
Additional coatings or films: none; anti-reflection; UV absorbing;
anti-blocking; anti-glare; hardcoat; capping layers (protecting
metal layers from oxidation or other compounds such as the
adhesive); adhesives; glues; reflective films; tinted films;
protective films; graphic films; patterned films; decorative
films;
[0106] Multi-region diffusers may have other different
configurations and are described further in U.S. patent application
Ser. No. 11/197,246. Additionally, the enhanced backlights and
light fixtures described in U.S. patent application Ser. Nos.
11/223,660 and 60/628,852 can be adapted to function as enhanced
electroluminescent signs or displays by combining them with image
or indicia forming means. The different configurations and
embodiments disclosed in the aforementioned provisional patent
applications are included as references and embodiments herein.
[0107] Preferred embodiments of the present invention are
illustrated in the following Example(s). The following examples are
given for the purpose of illustrating the invention, but not for
limiting the scope or spirit of the invention.
EXAMPLE 1
[0108] An enhanced electroluminescent sign in accordance with the
present invention, i.e., as illustrated in FIG. 11, has increased
spatial luminance uniformity, increased optical efficiency and is
of low production cost. A 16''.times.20'' direct-lit light box sign
(Ultra Thin Light Up Display from Bowman Displays) is used as a
benchmark for comparison with the enhanced electroluminescent sign
of this invention. The spatial luminance uniformity is measured at
0.5 cm intervals on either side of a region directly above the T8
fluorescent lamp in the white light box with the included standard
symmetric diffuser film (Sample STANDARD) with a Minolta CS-100
spectrophotometer. The angular luminance profile is measured at a
location directly above a fluorescent bulb with the standard
symmetric diffuser film with a Minolta CS-100 luminance and
tristimulous spot meter at varying 5 degree angular positions.
[0109] A light scattering film with anisotropic scattering profile
was prepared by blending and extruding a mixture of 70% polyester
and 30% polyethylene into a film and stretching the film to achieve
asymmetric dispersed phase domains as described in U.S. Pat. No.
5,932,342, the text of which is incorporated herein by reference.
The resulting 200 micron film had a full-width half maximum angular
luminance profile of 70.degree..times.10.degree. upon illumination
with collimated light. Sample A was prepared by optically coupling
a sheet of the anisotropic light scattering film to the light
source side of a 1.5 mm clear polycarbonate sheet such that the
major diffusing axis was perpendicular to the linear fluorescent
lamps in the sign. Sample B was prepared by optically coupling a
sheet of the anisotropic light scattering film to one side of a 1.5
mm clear polycarbonate sheet and optically coupling 2 sheets of the
film to the opposite side (viewing side) such that the major
diffusing axis of all of the films was perpendicular to the linear
fluorescent lamps in the light box. Sample C was prepared by
optically coupling 2 sheets of the anisotropic light scattering
film to one side of a 1.5 mm clear polycarbonate sheet and
optically coupling 2 layers of the film to the opposite side
(viewing side) such that the major diffusing axis of all of the
films is perpendicular to the linear fluorescent lamps in the light
box. The results of the spatial and angular luminance are shown in
FIG. 15 and FIG. 16, respectively.
[0110] The spatial luminance uniformity of the electroluminescent
signs using the Standard and Samples A, B, and C is shown in FIG.
15. The maximum luminance of the sign is clearly higher with the
Samples A, B, and C over the standard isotropic diffuser and the
results are shown in Table 1. This illustrates the increased
optical efficiency obtained by using anisotropic light scattering
regions. The spatial luminance uniformity can be compared by
examining the spatial distance from with center of the bulb
(maximum luminance point) at which the luminance falls to 70% of
the maximum due to the eyes capability of discerning luminance
variations. In the case where no diffuser is used at all, the
spatial luminance at 70% would be approximately 5 cm (the width of
the T8 fluorescent bulb). The larger the distance to the 70%
maximum luminance on either side of the bulb, the more uniform the
luminance. The spatial luminance at 70% is calculated from the
measured curves of FIG. 15 and is shown in Table 1. All of the
samples A, B, and C have larger spatial uniformities than the
standard isotropic diffuser, with the multiple layer anisotropic
scattering region separated by a non-diffusing polycarbonate
substrate (Sample C) providing the most uniformity. The angular
luminance distribution is illustrated in FIG. 16. Here, one may
also look at the angles at which the luminance falls to a value of
70% that of the maximum luminance. The calculated angular
full-width at 70% maximum luminance values are shown in Table 1.
The angular distribution of the standard and the Samples A and B
are similar in angles with only a minor difference of about 10
degrees over approximately 140 degrees. All are in the range of
acceptable viewing angles for most sign applications. Thus, the
asymmetric light scattering regions can increase the optical
efficiency (higher luminance), increase the spatial luminance
uniformity, while essentially maintaining the angular luminance
distribution. The resulting increase in efficiency can allow one to
use a lower wattage fluorescent bulb to achieve the same luminance
as the standard, thus reducing costs. TABLE-US-00001 TABLE 1 Sample
Sample Sample Standard A B C Increase in Max. Luminance 0% 70% 36%
24% from Standard Spatial Uniformity (full 10.5 10.75 12.5 14 width
@ 70% max) in cm Angular Uniformity (full 142 139 132 width @ 70%
max) in degrees
EXAMPLE 2
[0111] An enhanced electroluminescent sign in accordance with the
present invention can be produced as described in FIG. 8, that has
increased spatial luminance uniformity, increased optical
efficiency, reduced speckle and lower costs of production. This is
due in part to the use of the volumetric anisotropic scattering
region within the waveguide to more efficiently control the light
scattering. A light diffusing waveguide containing light scattering
particles in a host matrix material is created by extruding,
casting or coating, the mixture containing particles. The particle
chosen may be a polystyrene bead of diameter 5 .mu.m in the minor
axis and 20 .mu.m in the major axis dispersed at 10% concentration
in a host matrix of acrylic. Other choices of particles and host
matrix may provide equivalent performance. Asymmetry and alignment
of the asymmetry can be created by stretching or extrusion
processes. The resulting material suitable for waveguiding light
contains asymmetric particles and is optically coupled to a
reflector such as aluminized Mylar from DuPont by lamination using
pressure sensitive adhesive (PSA). A sign graphic such as a
screen-printed translucent vinyl material is disposed on the
opposite surface of the waveguide. A linear fluorescent bulb is
aligned along one edge that is parallel to the alignment of the
asymmetric particles. Further common sign components such as those
needed to contain the light source, waveguide and the electronics
and electrical elements of the sign are attached to create an
enhanced electroluminescent sign.
EXAMPLE 3
[0112] An enhanced electroluminescent sign, in accordance with the
present invention, can be produced as described in FIG. 11, that is
designed to have increased spatial luminance uniformity, increased
optical efficiency, reduced speckle and lower costs of production.
This is due in part to the use of the volumetric anisotropic
scattering element more efficiently controls the light scattering.
A light diffusing film containing light scattering particles in a
host matrix material is created by extruding, casting or coating,
the mixture containing particles. The particle chosen may be a
polystyrene bead of diameter 5 .mu.m in the minor axis and 20 .mu.m
in the major axis dispersed at 10% concentration in a host matrix
of acrylic. Other choices of particles and host matrix can provide
equivalent performance. Asymmetry and alignment of the asymmetry
can be created by stretching or extrusion processes. The resulting
film suitable for diffusing light contains asymmetric particles and
is placed on the exit face of a white light box containing parallel
cylindrical fluorescent bulbs. The axis of alignment of the
asymmetric particles is aligned substantially parallel to the
fluorescent bulbs as indicated in FIG. 12. The anisotropic
diffusing film may be attached to an acrylic substrate using a PSA.
A sign graphic such as a screen-printed translucent vinyl material
is located between the diffusing film and the outer surface of the
sign. The light from the fluorescent bulbs is diffused more in the
horizontal directions (perpendicular to the bulbs) than the
vertical making efficient utilization of the light and diffusing
the "hot spots" of the linear lamps. Further common sign components
such as those needed to contain the light source, the electronics
and electrical elements of the fixture are attached to create an
enhanced electroluminescent sign.
EXAMPLE 4
[0113] An enhanced electroluminescent sign, in accordance with the
present invention, can be produced as described in FIG. 13, that
has increased spatial luminance uniformity, increased optical
efficiency, reduced speckle and lower costs of production. This is
possible because the volumetric anisotropic scattering element more
efficiently controls the light scattering. A light diffusing film
containing light scattering particles in a host matrix material is
created by extruding, casting or coating, the mixture containing
particles. The particle chosen may be a polystyrene bead of
diameter 5 .mu.m in the minor axis and 20 .mu.m in the major axis
dispersed at 10% concentration in a host matrix of acrylic. Other
choices of particles and host matrix may provide equivalent
performance. Asymmetry and alignment of the asymmetry can be
created by stretching or extrusion processes. The resulting film
suitable for diffusing light contains asymmetric particles and in
placed on the exit face of a channel letter sign using LEDs as the
light source. The axis of alignment of the asymmetric particles is
aligned substantially in the vertical direction (y direction as
shown in FIG. 13) such that the light is diffused to larger angles
in the horizontal direction (x direction). The anisotropic
diffusing film may be attached to an acrylic substrate using a PSA.
Further common channel letter sign components such as those needed
to contain the light source, and the electronics and electrical
elements of the fixture are attached to create an enhanced
electroluminescent sign.
EXAMPLE 5
[0114] An enhanced electroluminescent sign in accordance with the
invention can be produced as described in FIG. 14, that is designed
to have increased spatial luminance uniformity, increased optical
efficiency, reduced speckle and lower costs of production. This is
possible because the multiple regions of asymmetric particles
optically coupled to the waveguide more efficiently control the
light scattering while reducing speckle contrast. A multi-region
light diffusing film containing light scattering particles in a
host matrix material is created by extruding, casting or coating,
the mixture containing particles. In between the light scattering
regions is a substantially non-scattering region. The particle
chosen may be a polystyrene bead of diameter 5 .mu.m in the minor
axis and 20 .mu.m in the major axis dispersed at 10% concentration
in a host matrix of acrylic. Other choices of particles and host
matrix may provide equivalent performance. Asymmetry and alignment
of the asymmetry can be created by stretching or extrusion
processes. A portion of the resulting anisotropic scattering
multi-region film containing asymmetric particles is optically
coupled to a transparent acrylic waveguide by lamination using a
PSA. Aluminized Mylar from DuPont is laminated to the face opposite
the scattering film using a PSA. A linear array of LEDs such as
LXHL-NW99 from Lumileds Lighting Inc. is aligned along one edge
that is parallel to the alignment of the asymmetric particles. A
sign graphic such as a screen-printed translucent vinyl material is
located between the diffusing film and the outer surface of the
sign. The light from the LEDs is diffused more in the horizontal
directions (perpendicular to the linear array of LEDs) making
efficient utilization of the light. The multiple light scattering
regions reduce the visibility of speckle, increase the luminance
uniformity while maintaining optical efficiency. Further common
sign components such as those needed to contain the light source,
the electronics and electrical elements of the sign are attached to
create an enhanced electroluminescent sign.
Equivalents
[0115] Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, numerous
equivalents to the specific procedures described herein. Such
equivalents are considered to be within the scope of the invention.
Various substitutions, alterations, and modifications may be made
to the invention without departing from the spirit and scope of the
invention. Other aspects, advantages, and modifications are within
the scope of the invention. The contents of all references, issued
patents, and published patent applications cited throughout this
application are hereby incorporated by reference. The appropriate
components, processes, and methods of those patents, applications
and other documents may be selected for the invention and
embodiments thereof. Related applications to this are
PCT/US05/31276, U.S. patent application Ser. Nos. 11/197,246,
11/223,660, and 60/628,852, the entire contents of which are
incorporated herein by reference.
* * * * *