Use of PolyCarbonate (PC) in LED Tubes
For LED tube lights, Plastic has become the material of choice, especially polycarbonate, because of its one-of-a-kind properties and the versatility it provides. Considerations include optical performance, mechanical properties and design flexibility.
An LED can be a very bright, unidirectional source, and manufacturers need materials that either make it possible for the light to shine directly through a surface for maximum brightness or provide uniform light distribution with no evidence of the light source for a more diffused effect. LED manufacturers and designers know how difficult it is to find a material that hides the LED source while permitting light to be transmitted at optimum levels. This is important not only for aesthetics but ensures optimal energy efficiency – a key goal of LED lighting technology.
The covering of a LED source regulates the amount of light that is transmitted or diffused. Customers often look for a material that offers high clarity and purity to ensure the optimum light transmission possible and maximum efficiency. However, depending on the application and the aesthetics needed in the end product, manufacturers are also concerned with the uniformity of light distribution. Polycarbonate can be tailored to specific needs for an application through the compounding process. Light transmission greater than 90% can be achieved for transparent polycarbonate resins. In some cases, the polycarbonate resins contain light diffusion additives, which are generally polymeric materials with a specific geometry, particle size, and refractive index that help obtain the desired balance of light transmission and light diffusion. For these polycarbonate resins, excellent light uniformity can be achieved over the entire surface of a part while hiding the bright LED light source, eliminating “hot spots.”
LEDs are solid-state devices with no fragile parts or filaments and are therefore very robust. In addition, LEDs have very long lifetimes relative to traditional light sources. Polycarbonate has proven outstanding toughness – far superior to acrylic and glass – and is an ideal material to use as a lens, cover, or housing that will ensure the LED lamp or luminaire remains undamaged over its long lifetime.
While glass and acrylics individually meet some of the requirements for LED lighting, they can both fall short when it comes to impact and heat resistance as well as design flexibility. Conversely, polycarbonate and polycarbonate blends are increasingly considered an ideal starting point for LED applications as they have the requisite basic properties and can be customized with other monomers, polymers, or additives to meet specific performance requirements.
For LED tubes, the most desired lens design is a form called “profile extruded,” which typically provides excellent hiding of the LED light source while providing the maximum amount of light transmission. Polycarbonate light diffusion grades are ideal for this application. In conjunction with their excellent toughness, polycarbonates also offer the transparency and uniform light distribution needed to help eliminates these troublesome LED hot spots. Transparent polycarbonate resins can achieve light transmission greater than 90%, while polycarbonate resins containing a light-diffusion additive can achieve excellent light uniformity, hiding the bright LED light source. The stiffness of the polycarbonate resin allows for good dimensional stability during the extrusion, and the outstanding toughness of polycarbonate allows the designer to make very thin lenses for optimizing the light transmission through the lens, which results in greater lumen output for the light source.
Despite their increasing use in general lighting applications, LED tubes do not have a standard shape and instead require design flexibility to obtain the desired figure (e.g., co-extruded tubes). One of the advantages of LED lighting is the freedom it offers manufacturers to be creative in their product designs. Unlike traditional incandescent lighting, the lighting industry is no longer restricted in aesthetic configuration and designers can actually “shape the light.” Plastic materials used for housing or covering the LED source can be formed into countless shapes and sizes through injection molding, injection blow molding, profile extrusion, and sheet extrusion/thermoforming processes.
Polycarbonate offers this flexibility in design options with a wide range of products available for specific processing requirements. In addition, because of the relative strength and toughness of polycarbonate, parts can be down-gauged for weight, energy, and cost savings. As mentioned earlier, this ability to be made into very thin parts also offers a great advantage for lighting applications as the thin diffusion lens allows more light to pass through, resulting in improved lumen output and greater efficacy, a highly desired feature for optical engineers.