Patent Application
20140268658
The present technology is directed to light diffusers that include both bulk and surface diffuser elements. One embodiment includes diffusing elements forming a structured coating on a substantially transparent substrate. Another embodiment includes a bulk diffuser with a structured surface. Methods for making and methods of using the light diffusers are also disclosed.
Diffusers are optical structures that scatter or diffuse light. Most diffusers fall into one of two classes: volumetric type or surface relief type. Volumetric (or bulk) type diffusers consist of an optical media substrate infused with a scattering particulate. The particulate may be reflective (e.g., titanium dioxide) and/or refractive (e.g., beads with an index of refraction differing from the substrate or medium in which they are suspended). Light traversing the volumetric diffuser will be reflected/scattered/refracted many times before exiting. Surface relief type diffusers (or SRDs) have a microstructure at the optical interface which will refract/diffract the incident energy in a “single-pass.” SRDs are characteristically higher efficiency compared with volumetric type diffusers because absorption losses and scattering losses are minimized. However, SRDs often produce an imperfect photometric profile. The present technology is directed to overcoming this and other deficiencies in the art.
This technology relates to a light diffuser comprising a transparent substrate and a plurality of lenses forming a complex lens structure on a first surface of the substrate, wherein the plurality of lenses comprise a non-homogenous material.
This technology also relates to a light diffuser comprising non-homogenous substrate wherein a first surface of the non-homogenous substrate forms a complex lens structure.
This technology also relates to a back lighted imaging media comprising a light source and a light diffuser of the present technology.
This technology further relates to a liquid crystal device comprising a light source and a light diffuser of the present technology.
This technology also relates to a method of diffusing light using a light diffuser of the present technology.
In accordance with the present technology, a new class of light diffuser that includes both bulk and surface diffuser elements is provided. One embodiment includes diffusing elements forming a structured coating on a substantially transparent substrate. Another embodiment includes a bulk diffuser with a structured surface. In either form, the volumetric diffuser concentration and refractive index difference between major and minor components in the non-homogenous material can be varied to control the light transmission, source obscuration, and bulk diffusion capabilities.
The light diffusers of the present technology can be used in lighting applications, including solid-state lighting, machine vision applications, automotive applications, transportation signaling applications, and displays, such as rear projection displays, back-lighted imaging media, liquid crystal display components and devices, and in processes for diffusing light.
Referring to
Referring to
As used herein, the term diffuser means a material that is able to transform specular light (light with a primary direction) to a diffuse light (light with random light direction). Light, as referred to herein, means visible light.
As used herein, transparent means a substrate with a total light transmission of about 50% or greater between 400 and 700 nm.
As used herein, a complex lens is a major lens having on a surface thereof a plurality of minor lenses (lenses smaller than the major lens that are formed randomly or in a desired pattern on the major lens, also referred to as microlenses). Thus, a complex lens is a multi-element lens with multiple microlenses at different positions. The number of minor lenses can vary from 2 to about 60, for example.
Suitable materials for the transparent substrate 2 are dimensionally stable, optically clear, and can have a smooth first surface 6. Such materials include, but are not limited to, polyolefins, polyesters, polyarylates, polyethylene terephthalates, polyphenylsulfones, cyclic olefin copolymers, polymethylmethacrylate, polyamides, polycarbonates, cellulosic esters, polystyrene, polyvinyl resins, polysulfonamides, polyethers, polyimides, polyvinylidene fluoride, polyurethanes, polyphenylene sulfides, polytetrafluroethylene, polyacetals, polysulfonates, polyester ionomers, and polyolefin ionomers. Copolymers and/or mixtures of these polymers can also be used. The transparent substrate is preferably not less than 20 microns thick and may be 2 or more millimeters in thickness.
Suitable materials for the majority component include, but are not limited to, monomers and/or oligomers that include epoxy, polyester, urethane, polyether, acrylate, and methacrylate or cationic monomers and oligomers. Various additives including fillers, free-radical initiators, and cationic initiators can be included in the material to improve its performance. See, for example, Sartomer Bulletin 4303 or 4201, the entire teachings of which are incorporated herein by reference. Examples of suitable materials are described, for example, in U.S. Pat. Nos. 5,903,399, 7,252,709, and 7,407,707, the entire teachings of which are incorporated herein by reference.
In one embodiment, the minority component is a scattering particulate, which may be reflective and/or refractive. Suitable examples of minority components include, but are not limited to, titanium dioxide and microbeads, e.g., styrene microspheres, divinyl benzene microspheres, methyl methacrylate microspheres, ethyleneglycol dimethacrylate microspheres, solid glass microspheres, and hollow glass bubbles. The light scattering particulate may also be comprised of these same materials in non-spherical shapes.
In another embodiment, the minority component is air bubbles. Air bubbles will perform similarly to hollow glass bubbles which have an index of refraction close to the index of refraction of the majority component. However, the use of air bubbles as the minority component eliminates the need to add, for example, a separate particulate to the majority component when forming the diffuser of the present technology. Rather, a desired amount and size of air bubbles can be produced, for example, by varying the speed of formation and curing of the majority component.
In a further embodiment, the minority component is luminescent. Suitable luminescent components include, but are not limited to, phosphors and anti-stokes compounds. For a given wavelength range of interest, this has the possibility of yielding greater than 100% efficiency since wavelengths outside the useful spectrum can be up/down converted to wavelengths within the application window. Alternatively, it is possible to strip out unwanted wavelengths with judicious choice of the material excitation energy. Such an embodiment could be used as another component in an LED based lighting fixture for enhancing the color rendering index (CRI).
In one embodiment, the majority component and minority component each have an index of refraction differing by at least about 0.1.
The ratio of the minority and majority components may vary. In one embodiment, the ratio of the minority and majority components is varied so the minority component is greater than about 0.01% of the total mass of the non-homogenous material.
In another embodiment, the non-homogenous material includes between about 0.2% and about 10% of the total weight of the minority component.
In yet another embodiment, the amount of minority component in the non-homogenous material is less than about 30% of the total mass of the non-homogenous material.
In one embodiment, the non-homogenous material has a majority component and minority component having indices of refractions equivalent at one wavelength but with differing dispersion characteristics at all other wavelengths. Depending on the concentration of minority component and aggressiveness of the complex lens (SRD) structure, the diffuser could transition between two completely different design photometrics over the spectrum (going from completely SRD dependent at the matched wavelength to strongly volumetric dependent as the wavelength is shifted).
The complex lenses of the present technology form an optic structure and, in one embodiment, are of a prescribed geometry. In one embodiment, the complex lenses are semi-spherical, meaning that the surface of each complex lens element (minor lens) is a sector of a sphere (but not necessarily a hemisphere). An example of a semi-spherical complex lens in accordance with one embodiment of the present technology is shown in
In one embodiment, each of lenses 4 and 24 is an individual complex lens.
The curvature, depth, size, spacing, materials of construction, and positioning of the complex lenses determines the degree of diffusion, and these parameters are established during manufacture according to the desired use of the diffuser of the present technology. The microstructure dimensions are preferentially scaled so that good structure representation of optical features may be imbued into a photoresist layer using laser lithographic mastering technology. Feature sizes can range in dimension from a minimum of about one micron to an unlimited maximum. An example of an unlimited feature dimension is a linear prismatic structure in which a fixed depth value is written around the circumference of the drum; since the processed drum is then used in a continuous roll-to-roll manufacturing process, the feature length has no boundary.
For applications in which optical elements will be used as part of a visual system, it will often be desirable for the feature size to be small enough as to be imperceptible by the unaided eye. Typically then feature sizes should not subtend more than one arcminute of angle over the distance between the observer and the optic. On the other hand, there are aesthetic benefits to having larger feature sizes, for instance in lighting in which feature elements on the scale of several millimeters or larger can yield a desirable visual aesthetic. Micron scale features can be made into millimeter or larger scaled visual aesthetics by substantially replicating feature slope angles over millimeter scale periodicities.
Overall optical substrate dimensions will be highly application dependent. Typical roll-to-roll processing will yield optical sheets on the scale of one meter wide by unlimited length. With finite element microstructure dimensions on the scale of tens of microns then this corresponds to embodiments yielding hundreds of millions to billions of optical elements per square meter.
In one embodiment, the light diffuser of the present technology is formed from a plurality of integral contiguous layers. The desired number of layers can be determined based on the desired optical design and can include, for example, between 2 and 4 layers. In one embodiment, a light diffuser 100 and a light diffuser 200 can be combined.
In one embodiment, the diffuse light transmission of the light diffusers of the present technology is at least about 50%, or between about 70 and 95%, or greater than about 92%.
In accordance with this technology, optical diffusers can be continuously formed from a radiation curable liquid material using a mold that defines a shape for optical structures to be formed upon the optical film. In particular, this involves placing the radiation curable liquid material in the mold, positioning a radiation transparent base film adjacent to the radiation curable liquid material in the mold, positioning a radiation source such that it can irradiate the curable liquid material while the radiation curable material is in the mold, thereby forming the shape of the optical structures, and curing the liquid material by exposing it to the radiation source.
The light diffusers of the present technology can be used in combination with a light source or display in lighting applications, including solid-state lighting, luminaire lighting, machine vision applications, automotive applications, transportation signaling applications, and displays, such as rear projection displays, back-lighted imaging media, liquid crystal display components and devices, and in processes for diffusing light. Thus, providing a light diffuser of the present technology in combination with a light source or display can produce a diffused light having a desired photometric profile.
The light diffuser is tailored to the light source to be diffused in the above-described applications. In accordance with the present technology, the complex lens (SRD) structure of the light diffuser can be tailored to create a variety of photometric profiles and the bulk diffuser portion including the non-homogenous material can be formulated to augment the desired optical design, or to provide smoothing of the photometrics.
In accordance with the present technology, if the minority component (particulates/air bubbles) is positioned in the substrate to form a non-homogenous substrate, as shown in
Optical structures were created in a mathematical model and this model was used to create a tool using a proprietary method. The microlens sag profile was tailored for the specific photometric application requirements. In the case of the DELTA2 design for which photometric plots are included herein, the surface sag profile was fit to a simplified asphere equation as shown in Eq. 1:
where sag(ρ) represents the surface profile with respect to the spatial coordinate (ρ) of the kernel microlens which is tiled up en-masse to cover the film diffuser area. The coefficients for Eq. 1 which may be used for generating the surface sag profile for the DELTA2 design are as follows: c=0.0182, A4=6.964×103, A6=1.197×107 and Ag=4.122×109. The tool was filled with energy cure acrylates that were formulated in a separate operation. For the various diffusers formed and tested, the energy cure acrylates included multiple multifunctional acrylate oligomers and monomers in a blend which are in a radiation-curable coating formulation. The blend of materials included a blend of aliphatic urethane acrylate oligomers, propylene diacrylates, dimethanol diacrylates, bisphenol diacrylates, polyester acrylates, polystyrene, alkane diols, silicone diacrylates, benzotriazole, and hindered amine light stabilizers (HALS), with hydroxy-cyclohexyl-phenyl-ketones, trimethylbenzoylphenyl-phosphineoxides, and/or other catalysts that can trigger the cross-linking reaction. A transparent substrate was placed in contact with the tool coated with the energy cure acrylates and this was exposed to an energy source, in particular UV radiation, to form diffusers having a transparent substrate and a plurality of complex lenses on a first surface of the substrate. The light diffusers that were made are set forth in Table 1, below:
A comparison of the various diffuser designs with several different acrylate formulations and a prior art diffuser can be seen in
As can be seen in
Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/780,888, filed Mar. 13, 2013, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61780888 | Mar 2013 | US |
