LED lighting has captivated the commercial, residential, and architectural lighting industries for over a decade and it shows little indication of slowing down. Energy-efficient and customizable, in both form and function, optical designers continue to use LEDs to change the way we think about lighting our homes, roadways, offices, coffee shops, and factory floors. An often-forgotten aspect of LED lighting is the diffuser tasked with efficiently managing the light in a manner that is comfortable to the viewer’s eye. So, where do Bixby’s diffusers position themselves in the LED light diffusion market?
What is Diffusion?
To start, let’s define diffusion. Diffusion of light is taking concentrated light and spreading it to achieve a desired characteristic of intensity, aesthetic, and shape. There are two primary methods of light diffusion: volumetric diffusion and surface diffusion.
Volumetric Diffusers
Volumetric diffusion utilizes the incorporation of filler particles in a medium to refract or scatter, incoming light. Particle size, particle size distribution, chemistry, and loading level will all affect the light diffusion properties. Typically, these particles are opaque in nature. The interaction of light with the particles causes it to both reflect and scatter. These diffusers often have a “frosted” appearance and offer excellent hiding power of LED hot spots. Coloring a transparent thermoplastic with a finely dispersed pigment is also an example of this diffusion mechanism. As the number of particles increases in the material, more incoming light is scattered, creating a greater extent of diffusion.
There are two important considerations to think about with volumetric diffusion, and both are related to an overall loss of light transmission. The first is absorption. When light interacts with these pigment particles, it is not only reflected at their surface but also absorbed. A blue pigment, for example, will absorb all wavelengths of light but blue. This inherently causes a decrease in the total transmission of light by an increase in opacity, negatively affecting the luminous efficiency of the diffuser. In addition, absorption characteristics are wavelength dependent and may change based on the properties of the LED’s themselves. The second is the random nature of the scattering phenomena. When light interacts with these particles, not all of it is scattered through the diffuser, some is reflected internally and lost. This also decreases transmission, therefore hurting efficiency. This “random scattering” principle also leads to other notable drawbacks, such as a lack of control over the light distribution. For example, there is no control of light that scatters at high angles. This is light that contributes to glare and poor UGR ratings.
From a polymer materials and processing perspective, these diffusion methods can also be challenging. Careful consideration must be taken to ensure proper particle size and distribution are met of incoming raw materials. Converters must also recognize the importance of proper dispersion of these fillers throughout the polymer medium without agglomeration. Mechanical properties of filled polymer systems may also suffer. Most notably, impact toughness is reduced through the introduction of stress concentrations at the filler-base resin interface.
Surface Diffusers - Gross Texturing or Embossing
Surface diffusion is the second method that can be used for managing light. These diffusers incorporate geometric features on a film, sheet, or part surface that interact with light through refraction. In its simplest form, any degree of texture on a transparent material's surface will refract and spread incoming light. This is because these surface features change the angle of incidence of incoming light to the polymer interface, consequently changing the angle of refraction. For example, embossed ridges, prisms, matte, or brush finishes create the opportunity for angle of incidence changes that refract the light to form a wider, more diffused output. The most critical distinction between volumetric diffusers and surface diffusers is that surface diffusers offer much greater extents of light transmission and overall efficiency. This results in a trade-off with hiding power. The extent of this hiding power is dependent on the degree of surface texture implemented. Greater degrees of roughness for example will increase hiding power but can hurt transmission efficiency. This is because light is refracted so greatly that it may be reflected back into the diffuser medium and lost.
Surface Diffusers with Engineered Optics
While surface diffusion may be accomplished through gross texturing or embossing of a material, a major drawback is that there is only rudimentary control of where the light goes once refracted and diffused. A sub-set of surface diffusers replaces these gross surface textures with the use of highly engineered, calculated surface texture optics. These diffusers offer much greater extents of beam management, controlling not only the extent of diffusion but generating a specified distribution of outgoing light. This may range from a desired circular angle to highly asymmetric axial distributions such as an ellipse. Commonly, these diffusers implement features on the scale of microns to achieve this. These intricate patterns are sometimes so small that they create significant challenges when trying to emboss the design in a thermoplastic sheet such as polycarbonate, acrylic, polyester, etc. A typical method of manufacture is UV cast and cure, where a layer of UV resin is cast and cured onto a polymer film substrate to form a two-layer construction. Consideration must be taken to ensure 1) there is proper adhesion between the UV resin and polymer substrate during both production and throughout the product lifespan, 2) the ultimate light distribution is not affected by any change in refractive indices of the two materials and 3) both the polymer substrate and UV cured thermoset resin must meet the application properties of the luminaire, with respect to moisture, chemical and UV resistance, thermal, and mechanical properties. In addition, it is uncommon that these features can be applied directly to a thick rigid substrate that has enough body to support its own weight. To achieve this, thin film substrates with UV cast features may be laminated onto the thicker sheet or molded components. This solution may meet the product goals, however ultimately it introduces more design and manufacturing complexity by adding components in the product structure that have opportunities to fail in application or vary in production which can lead to non-conformance.
Bixby’s Unique Surface Diffusers
Bixby’s optical diffusers implement the theory of surface diffusion but are distinct in that they address many of the shortcomings presented in the preceding paragraph regarding cast and cure surface patterns and their lamination. At Bixby, our proprietary manufacturing techniques have enabled us to directly incorporate calculated surface optics, what we call “facets”, into a monolayer sheet or film. This means no risk of delamination, simplified product designs, and the ability to utilize a full range of transparent thermoplastic materials tailored to your specific end-use requirements. These techniques aim to add increased product performance and convenience to lighting manufacturers in both their existing product architectures and new innovations. The novel technology also fulfills needs not currently met by the market. Coupled with unique and customizable optical software to match current distributions or generate new ones, this technology serves to increase design freedom without compromising product performance.
Bixby’s diffuser technology is custom, calculated, and simple. Dedicated to innovation, Bixby is pleased to provide the market with this technology and our technical team is ready to meet your manufacturing, application, and material needs. Contact a technical expert today to learn more about how this technology may benefit you.
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