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The main application of optical PC in LED lighting
- May 31, 2018 -

The main application of optical PC in LED lighting

PC, also known as polycarbonate, is an acronym for Polycarbonate. PC is a high molecular polymer containing a carbonate group in the molecular chain, and can be classified into various types such as aliphatic, aromatic, and aliphatic-aromatic depending on the structure of the ester group. At present, mainly aromatic polycarbonates are applied and industrialized. Polycarbonate is an excellent engineering plastic with a density of approximately 1.20 g/cm3. Colorless transparent plastic parts made of PC, the visible light transmittance can reach about 90%. The main uses of PCs include optical lighting, electronic appliances, automotive aviation and medical care. In general, we will apply to the field of optical lighting. Transparent, diffuse or white high reflectivity PC materials with good optical properties are called optical PCs.

As the adoption rate of LED lighting products continues to increase, lighting manufacturers are looking for materials whose performance exceeds those used in traditional lighting applications to drive innovative designs and form factors, increase lighting efficiency, and address ongoing adoption costs. Although lighting manufacturers have always used organic glass (PMMA) - followed by glass - for solid-state lighting (SSL) applications, PCs are increasingly becoming the material of choice for lenses, transmissive enclosures, lamps, light guides, diffusers, and reflectors. . Today, about 90% of LED replacement bulbs that replace incandescent bulbs are made from PC materials.

LED designers can achieve many benefits by choosing a PC (rather than glass and PMMA), including greater impact and heat resistance, improved flame rating, and increased design flexibility. However, because glass and PMMA have high light transmittance and strong weather resistance, they are still competitors of PCs, but the latest class of special PCs quickly bridge this gap. As candidates for LED devices, polycarbonate not only presents a direct challenge to glass and PMMA, but also promotes the continuous advancement of residential, commercial, and outdoor LED designs.

PC and PMMA main performance comparison

Durability and impact resistance are necessary conditions for the residential environment because residents often drop when installing the lamp or improperly handle the replacement parts. The impact resistance of a PC to break a sample under flexural impact is expressed in the laboratory as kJ/m2 (kilojoules per square meter) measurement units, which is much higher than the impact resistance of glass and PMMA. In the actual impact test, the performance of the PC is 10 times that of the PMMA and 30 times that of the glass.

LED devices made with PCs are also safer than those made with PMMA because of their obvious advantages in flame retardancy and heat resistance. According to the UL 94 standard, some PCs are rated as "5VA" - the highest flame retardancy rating - the UL 94 standard classifies plastics according to different directions and thickness of combustion. PMMA was rated UL 94 "HB" rating, which is also the lowest rating. In addition, the PC can also be used continuously at temperatures up to 130°C, whereas PMMA can only be used at temperatures up to 90°C. Table 1 summarizes the PC and PMMA features that are important to designers of LED lighting products.

In order to increase the LED demand in the residential environment, the lighting designer must also solve the quality problem of the LED lighting equipment, making the lighting softer and closer to the incandescent lamp. The opalescent or matte-effect diffusion material shields the LED light source and helps distribute the light evenly, minimizing glare. If there is no diffusion, the LED light source will produce dazzling white bright spots.

At the same time, designers must maintain a balance between the aesthetic needs of soft white light and light transmission. Excessive diffusion may mean excessive loss of brightness, which reduces lamp efficacy.

The PC excels at maintaining a delicate balance between diffusion and light transmission. The new generation of polycarbonate can shield bright spots without affecting light transmission. When used in an LED dome or transmissive cover, the PC provides effective diffusion without the need for secondary lenses or other optical components, thereby reducing cost, complexity, and weight. Diffusion plates made with PMMA usually require a multilayer structure, which increases the weight and complexity of the LED design.

Table 2 shows the light transmittance and light scattering provided by the LED grade available to today's LED designers. Transparent grade 1mm SABIC's LEXANTM LUX C resin combination has a light transmittance of 91.5%, a significant improvement over conventional PCs with a light transmission of approximately 89%, second only to PMMA with a light transmittance of 92%. For lighting applications where greater diffusion is required, the LEXANTM LUX C resin diffusion grade spreads the light (shown in Table 2) to the light diffusion (DLD), which is half the angle of the incident light without significantly reducing Transmittance.

Commercial and industrial LED lamp manufacturers also face many challenges in the residential market. Lighting design must be functional, stylish, light and smart, while achieving high light efficiency and light uniformity.

To reach these complex standards, manufacturers are struggling to find a variety of materials to achieve design flexibility in this regard PC far better than glass and PMMA. For example, PC can be used to form sharp corners and notches - these design features further highlight the weakness of PMMA in impact strength. In addition, PMMA does not maintain high durability and hardness in ceiling mounted LED applications like PCs.

Compared to other materials such as glass, which require the use of relatively low-efficiency adhesive assembly, PCs can be used for snap-fit applications. According to EU-related reports, unlike adhesive components, LED lamps and luminaires made of snap-fit connections can be easily disassembled without damaging components, reducing life-cycle costs and environmental impacts such as scrapping costs.

Using polycarbonate

Although refractive index (RI) differences must be considered, designers and OEMs can still use the PC to develop products in much the same way as products developed using PMMA and glass. Although the same predictive modeling tools can be used, SABIC also provides a Bidirectional Scattering Distribution Function (BSDF) file, enabling product engineers to simultaneously predict the design of transparent and diffuse materials. In addition, the PC can be processed using the same type of molding machine as PMMA - injection molding machines, extruders, and blow molding machines. Using a PC that meets the UL 94 flame retardant rating also shortens product development time and potentially eliminates the need for equipment burn testing.

Although the outlook is bright, LED technology is still at a relatively early stage of development, and it still needs to enter the mass market on a large scale, thus becoming the main lighting method for residential, commercial and outdoor environments. Manufacturers and designers are facing these challenges, and excitingly, new designs are emerging every day. In order to address the ever-changing complex regulatory issues in the LED industry, continuous investment in new and improved PC materials is needed. SABIC will always work with the entire LED lighting industry to promote the development of the next generation of LED.