Enhanced electroluminescent sign
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.
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
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
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.
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.
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.
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.
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
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.
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.
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.
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
DETAILED DESCRIPTION OF THE INVENTION
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.
For convenience, certain terms used in the specification and examples are collected here.
“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.
“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.
“Speckle” includes scintillation or the optical interference pattern visible on a diffusing element.
“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.
“Scatter,” “Scattering,” “Diffuse,” and “diffusing” as defined herein includes redirecting of light by reflection, refraction or diffraction from particles, domains, surfaces, layers or regions.
“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.
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.
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.
“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 (α) does not satisfy the condition
where n1 is the refractive index of the medium inside the light guide and n2 is the refractive index of the medium outside the light guide. Typically, n2 is air with a refractive index of n≈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×3 micron ellipsoidal dispersed particles or it may be a 3 millimeter diffuser plate with 2.5 micron×70 micron dispersed phase particles.
“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 (α(½)) 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° and −35° were measured to have one-half of the maximum luminance in the horizontal direction, the AOV α(½) in the horizontal direction for the screen would be 70°. The AOV at full-width at one-third maximum (β(⅓)) and the AOV at full-width at one-tenth maximum (χ( 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.
The “asymmetry ratio” or “anisotropy ratio” is the horizontal AOV α(½) divided by the vertical AOV α(½), and thus is a measure of the degree of asymmetry between the horizontal luminance and the vertical luminance of the diffuser.
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.
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.
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.
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.
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.
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.
In one embodiment of this invention the disperse domains have a refractive index np1 different from the host matrix material refractive index nm1 defined by at least one of |nmx1−npx1|≧0.001,|nmy1−npy1|≧0.001, or |nmz1−npz1|≧0.001 to provide sufficient light scattering. The differential refractive index (ΔnMP) defined as the absolute value of the difference between the index of refraction of the matrix (nM1) and the index of refraction of the particles (np1), or |nM1−np1|, 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.
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.
When more than one type of non-spherical domains are used within an anisotropic light scattering region, they may have a refractive index np2 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).
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.
The average dimension of a dispersed domain or particle in the x, y, or z direction in the matrix may be from about 1 μm to about 30 μm, preferably from about 2 μm to about 15 μm, and most preferably from about 2 μm to about 5 μm in the minor dimension.
The average dimension of a dispersed domain or particle in the x, y, or z direction in the matrix may be from about 2 μm to about 2 cm, preferably from about 5 μm to about 1 cm, and most preferably from about 10 μm to about 500 μm in the major dimension.
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.
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.
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.
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).
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).
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.
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.
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 1/10th the wavelength of light. In a preferred embodiment, the size of the particles are less than 1/20th 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.
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.
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.
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:
- 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;
- 2. Sign graphic type: transparency; printed vinyl; translucent polymer; glass; shaped light emitting indicia;
- 3. Sign graphic location: one face; more than one face; along an edge; along at least a portion of one surface;
- 4. Waveguide type: none; scattering; non-scattering; polymer; glass; colorless; tinted; dyed; curved; planar; parallel faces; non-parallel faces; tapered;
- 5. Number of scattering regions: one; two; more than two;
- 6. Scattering region:
- 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;
- b. Scattering region thickness: greater than 5 microns and less than 300 mm;
- c. Dispersed domain shape: symmetric; or asymmetric; spherical; non-spherical; or a combination of both; varying through the volume; varying in a pattern; random;
- d. Dispsersed domain size: between 1 μm and 30 μm in the minor axis; between 2 μm and 2 cm in the major axis; varying through the volume; varying in a pattern; random; small domain size distribution; large domain size distribution;
- e. Light scattering domain refractive index: average refractive index np wherein |np−nm|>0.001; refractive index npx and npy, in the x and y directions respectively, wherein |npx−nm|>0.001; |npy−nm|>0.001; or |npy−nm|>0.001 and |npx−nm|>0.001.
- f. Light scattering domain concentration: constant; varying throughout the volume; regularly varying; random;
- g. Separation between individual scattering regions: greater 5 microns and less than 300 mm.
- 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;
- 7. Reflector type: none; metallized coating; multi-layer reflective plastic;
- 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;
- 9. Number of light sources: one; two; more than two;
- 10. Individual light source color: primary color; non-primary color; white; cool white; warm white;
- 11. Light source optics: none, collimating lens; collimating reflector; integrator; refractive lens; reflective lens; anisotropic refracting or scattering element to increase uniformity;
- 12. Waveguide material: none; polymer; rubber; plastic; glass;
- 13. Waveguide extraction method: symmetrically diffusing regions; asymmetrically diffusing regions; printed dots; prismatic shapes; surface relief profile;
- 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;
- 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;
- 16. Bulb or tinted region color: none, primary color; non-primary color;
- 17. Tint location: none; within substrate; within light scattering region(s); within a non-scattering region; a separate film or region;
- 18. Diffuser substrate type: none; rigid; flexible; substantially transparent; substantially opaque;
- 19. Substrate location: none; behind the reflector; in-between the light scattering regions; in front of the light scattering regions;
- 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;
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.
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.
An enhanced electroluminescent sign in accordance with the present invention, i.e., as illustrated in
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°×10° 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
The spatial luminance uniformity of the electroluminescent signs using the Standard and Samples A, B, and C is shown in
An enhanced electroluminescent sign in accordance with the present invention can be produced as described in
An enhanced electroluminescent sign, in accordance with the present invention, can be produced as described in
An enhanced electroluminescent sign, in accordance with the present invention, can be produced as described in
An enhanced electroluminescent sign in accordance with the invention can be produced as described in
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.
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 nc1 and a first dispersed phase material of refractive index nd1 wherein |nc1−nd1|>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 δ 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 nc2 and a second dispersed phase material of refractive index nd2 wherein |nc2−nd2|>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: ndx1≠ndy1, ndx1≠ndz1, ndy1≠ndz1, ncx1≠ncy1, ncx1≠ncz1, ncy1≠ncz1.
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 n1 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 θ such that θ < sin - 1 ( 1 n c ) or θ < sin - 1 ( 1 n t ).
28. The electroluminescent sign of claim 1 wherein a first set of image or indicia is viewable at a first angle α and further comprising a second means for displaying a second set of image or indicia viewable from a second angle β such that α≠β.
29. The electroluminescent sign of claim 28 wherein 0°≦|α−β|≦180°.
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.
International Classification: G02B 6/26 (20060101);