the glass and PMMA LED lamp material Why is the PC to win?

the glass and PMMA LED lamp material Why is the PC to win?

Introduction: LED designers have achieved many advantages by choosing PC (not glass and PMMA), including stronger impact resistance and heat resistance, improved flammability levels and increased design flexibility.

With the increasing adoption rate of LED lighting, lighting manufacturers are pursuing materials other than traditional materials for lighting applications to promote innovative designs and shapes, improve efficiency, and overcome ongoing cost barriers. Although traditionally manufacturers use polymethyl methacrylate (PMMA) in solid-state lighting (SSL) applications-followed by glass. Nowadays, polycarbonate resins (PC) are increasingly used as lenses, lampshades, lamp tubes, catheter columns, diffusers and reflectors. Today, approximately 90% of retrofit LED lamps that replace incandescent lamps are made of PC materials.

LED designers have realized several advantages by choosing PC (not glass and PMMA), including stronger impact resistance and heat resistance, improved flammability levels and increased design flexibility. Although glass and PMMA remain competitive with PCs due to their high light transmittance and strong weather resistance, the latest professional PCs are rapidly closing the gap. As a candidate material for LED devices, polycarbonate poses a huge challenge to glass and PMMA, and is driving advances in residential, commercial, and outdoor LED design.

PC opens the residential market

Many countries have begun the transition, away from traditional lighting sources, thanks to consumers' high attention to energy saving and emission reduction, and government regulations to promote the phasing out of inefficient light bulbs. However, in order to fully replace incandescent lamps and compact fluorescent lamps (CFL), LED must solve the cost problem, cost is still one of the main obstacles to enter the mass residential market. As demand grows, consumers need to see and understand the benefits of investing in longer-life technologies.

Durability and impact resistance are important standards in a residential environment, because it is common for residents to drop when installing lamps or to improperly handle lamp replacement. The impact resistance provided by PC is measured in kJ / m2 (kJ / m2) when the sample is broken by bending impact in the laboratory, which is significantly higher than that of glass and PMMA. In the actual impact measurement, the performance of PC exceeds 10 times of PMMA and 30 times of glass.

LED devices produced using PC are also safer than those produced using PMMA, which does not perform well in terms of flame retardancy and heat resistance. According to the UL 94 standard, certain PCs have achieved a "5VA" rating, which is the highest level of flame retardancy. On the other hand, PMMA received a "HB" rating of UL 94, which is the lowest in the ranking. In addition, PC can be used continuously at temperatures up to 130 ° C, while PMMA can only reach 90 ° C. Table 1 summarizes the important characteristics of PC and PMMA for the reference of developers of solid-state lighting products.


Table 1. PC and PMMA specifications comparison

Produce softer solid-state lighting

In order to increase the demand for LEDs in residential environments, lighting designers must also address the quality issues of LED lighting equipment, making the lights softer and closer to incandescent bulbs. Diffusion materials with milky white or matte effect can shield the LED light source, help to distribute light evenly and reduce glare. If there is no diffusion, the LED light source will produce dazzling white bright spots.

At the same time, designers must balance the relationship between the aesthetic needs of soft white light and light propagation. Too much diffusion may mean excessive light loss, reducing lamp efficiency.

PCs are good at achieving a delicate balance between diffusion and light propagation. A new generation of polycarbonate can shield hot spots without affecting light transmission. When used in LED domes or lens covers, PC provides effective diffusion without the need for secondary lenses or components, thereby eliminating cost, complexity, and weight. Diffusers manufactured using PMMA usually require multiple components, increasing the weight and complexity of the LED design.

Table 2 shows the PC grade transmission and light scattering available to LED designers today. The SABIC LEXAN LUX C resin product of the transparent grade provides 1 mm 91.5% light transmission, which is a significant improvement over 89% of the traditional PC, second only to 92% PMMA. For lighting applications that require greater diffusion, LEXAN LUX C resin diffusion stage can diffuse light (shown in Table 2) to the degree of light scattering (DLD), or observe an angle of half the brightness of the incident light without significantly reducing light transmission .

Table 2. Transparent and diffuse PC grade light transmittance and light scattering

Creating lighting uniformity and consistency also poses difficulties for industrial and commercial LEDs, but PCs have proven to be effective in these environments. Intematix is a manufacturer of fluorescent materials and optics for LED lighting. The company chose SABIC's LEXAN LUX resins at the transparent, diffuse, and reflective levels to make the ChromaLit linear lighting system (Figure 1).



figure 1. Intematix's ChromaLit lighting system uses remote phosphor technology and polycarbonate-based optics

ChromaLit uses remote phosphor technology, which uses phosphor components separate from the blue LED energy to produce better light diffusion. The separation of the phosphor and the energy source produces better illumination uniformity. The ChromaLit linear system provides naturally uniform, high-quality light. When used with the most efficient blue LEDs, the conversion efficiency of the system can be as high as 215 lm / w or as high as 163 lm / W.

Design flexibility for commercial lighting

Manufacturers of LED lamps for commercial and industrial use also face many of the same challenges as the residential market. The lighting design must be practical, attractive and light, while also providing high light efficiency and light uniformity.

To meet these complex standards, manufacturers are looking for materials that can provide design flexibility, and glass and PMMA lag behind PCs in this area. In particular, PC can be used to produce sharp corners and notches-this design feature further strengthens PMMA's weakness in impact strength. In addition, PMMA cannot maintain high durability and hardness in ceiling LED applications like PC, as shown in Figure 2.



Figure 2 Glass and PMMA cannot achieve sharp corners and notches like PC, nor can they maintain high durability and hardness in LED applications like PC

Compared with other materials (such as glass), PC can also be used for snap-fit applications. Unlike adhesive components, LED lights and lamps made using snap connections can be easily disassembled without damaging parts, thereby reducing life cycle costs and environmental impact. For more information on life cycle impact, see Table 3.



table 3. Comparison of environmental impact and life cycle between LEXAN resin and PMMA

Another fundamental obstacle facing commercial LED designers is the release of light inside the optical system. This design defect can reduce the light output while generating unnecessary heat, thereby reducing the reliability and service life of the device. The lens made of PC has a high refractive index, which can help optimize light extraction, and can also integrate the reflector into the LED module, thereby achieving a thinner lens and a lighter design. Using PC lenses, PC reflectors can also be effectively integrated into optical systems. By using lenses and mirrors to maximize the illumination of the LED module, PC is significantly better than PMMA.

PC also provides manufacturers with a choice of processing methods, from injection and blow molding to extrusion, which supports in-mold injection to form dynamic and curved shapes. Although PMMA can also be processed by various methods, considering the global warming and total energy demand, PC materials have more obvious advantages in terms of sustainable development and life cycle impact (see the carbon entry in Table 3).

Improve outdoor LED performance

LEDs are increasingly used in architectural lighting, exterior and street lighting, and automotive applications. While facing many of the same challenges as residential and industrial environments, outdoor LED designs must address the effects of long-term exposure to the sun, rain, wind, heat, humidity, and cold.

Although PMMA outperforms PCs in weather and ultraviolet (UV) radiation resistance, PCs have made progress in these areas. For example, SABIC's LEXAN SLX resin is specifically designed to close the gap between PC and PMMA in outdoor applications. LEXAN SLX resin can resist yellowing caused by ultraviolet exposure, and maintain its gloss, color stability and mechanical properties for more than five times longer than standard PC. Standard PC degrades due to ultraviolet radiation, reducing the ductility of the component and making it brittle. The outdoor illumination lens in Figure 3 shows a comparison of the yellowing of components made with LEXAN SLX resin and standard PC after 2900 hours of ultraviolet (UV) exposure. To capture the difference, the lens was placed in a hot room equipped with a 175W metal halide (MH) lamp and placed on the refractor at 120 ° C for 2900 hours.



image 3. LEXAN SLX resin (left) and standard PC with UV additives (right)

The evolution of polycarbonate

Advances in PC technology have significantly improved the suitability of PCs for LEDs. Material manufacturers such as SABIC have invested in the development of PC materials to expand design freedom through lighter weight, better mechanical properties, higher aesthetics and fewer secondary operations.

Figure 4 compares the thermal aging of SABIC's LEXAN LUX resin grade with a standard PC using UV additives. When tested at 130 ° C for 5000 hours, the standard PC showed a greater color shift compared to the two grades of LEXAN LUX resins tested (2180T and 2110T) —indicated by the increase in incremental Yi or the yellow index .

Figure 4. 2.5 Color shift of 5 mm material after thermal aging at 130 ° C

Due to the extremely long life of LED devices (up to 10-15 years), life is also a key factor for LED components and materials. As shown in Figure 5, SABIC's LEXAN LUX resin grade has a better transmission percentage than standard PC after heat aging for 2000 hours.



Figure 5. 2.5 Transmittance deviation of 5 mm material after thermal aging at 130 ° C

Use polycarbonate

Although the difference in refractive index (RI) must be taken into account, designers and OEMs can develop products in the same way as PMMA and glass. Although the same predictive modeling tools can be used, SABIC can also provide bidirectional scattering distribution function (BSDF) files, allowing product engineers to predict the results of their designed transparent and diffuse materials. In addition, PCs can also be processed using the same types of molding machines as PMMA—injection molding machines, extruders, and blow molding machines. Using a PC that meets the UL 94 flame retardant rating can also shorten product development time and may eliminate the need for equipment combustion testing.

Although the future of LED technology is bright, it is still at a relatively early stage of development and has not yet achieved a large-scale market breakthrough, which has become the main form of lighting in residential, commercial and outdoor environments. However, manufacturers and engineers are facing these challenges, and exciting new designs appear every day. Solving the complex and constantly changing specifications of the LED industry requires constant investment in new and improved PC materials。If you want to know more about it please do not hesitate to contact me. WhatsApp:+86-15966835076.