Diffuse Plastics and Optical Design

There is a glowing trend in illumination optics: diffuse plastics. A quick trip through the aisles of an auto show or even down the lighting aisle of a home improvement store will leave you with the sense that the modern aesthetic requires almost every type of light to have a smooth lit and unlit appearance. And why not? Diffuse plastics give optical designers the ability to sculpt light in three dimensions. Want a candelabra bulb to glow in the shape of a flame? Diffuse plastics. Want the daytime running lamp in your car’s headlight to look like a furrowed eyebrow on the front of your car? Diffuse plastics. The possibilities are nearly endless, and utilizing diffuse plastics in optical design has become mainstream.

Historically, diffuse plastics have been employed for decades, often relegated to the task of hiding flaws in an optical design. Got a hotspot in your indicator? Use a diffuser to homogenize the light. By making the diffuse plastic the star in an optical design, designers have added an extra layer of complexity that didn’t previously exist. They now need to account for the diffusion of the plastic in the design phase, instead of adding it at the end or during the prototype phase.

Two truisms follow from this:

• The tools that an optical designer uses must be able to accurately model the effects of diffusion, and
• The diffuse optical properties of the plastic must be known

Most optical design tools support some form of diffuse optical properties for bulk scattering; the hard part is acquiring the optical properties of the plastic. Those who design with diffuse plastics typically fall into two categories: designers who will choose a plastic from a stock vendor or designers who will define the level of diffusion their design needs and make or procure a custom plastic. There are many plastic vendors who provide stock diffuse plastic; Covestro, MOCOM, Röhm, and SABIC are just a few. However, the optical properties of diffuse plastics are not readily available from many vendors. Synopsys offers the SmartStart Library, which contains dozens of diffuse plastics for use with LightTools and LucidShape. Additionally, measurement vendors, including the Synopsys Optical Solutions Group, have proprietary methods to measure the optical properties of diffuse plastic. When designing with a custom diffuser, it is inconvenient to measure every iteration of the diffuse plastic. Instead, having a tool that allows the designer to change the optical properties on-the-fly is important.

If you’d like to learn more about modeling diffuse plastics, check out the white paper on our website. The paper describes a method for modeling custom diffuse plastics using physically measurable quantities, such as the weight of the plastic and the weight of the particulates (such as titanium dioxide) used to make the plastic diffuse.