LED TECHNOLOGIES SALES MANAGER
Optical design is one of the most challenging stages for LED lighting product developers. An incorrect choice at this stage can seriously disrupt the structure of the entire system and the quality concept. In most applications, in order to emit or focus the angle of the light from the LED, and to reach the desired level of light intensity in the area to be illuminated, a secondary optics such as a lens, reflector or TIR optics are needed outside the optical structure (primary optics) of the LED. This secondary optical glass can be made of various optically transparent raw materials such as polymethylmethacrylate (PMMA), polycarbonate (PC) and silicon, and the optimum material largely depends on the requirements of the specific application, as each material has some advantages and disadvantages over the other. Now, let’s take a look at these advantages:
PC (Polycarbonate):
It is an intrinsic choice for applications that require transparency and high tensile strength. Since it is thermoplastic, it can be reshaped into various shapes and sizes without any deterioration. The PC also has high impact resistance. It is flexible, resistant to chemicals and durable. It has a higher softening temperature (130°C) than PMMA. Due to these characteristics, it is often used in applications such as automotive parts, protective equipment, digital discs and outdoor lighting fixtures. However, PC gradually turns yellow when exposed to UV light, so it needs to be covered with a UV-resistant surface. Also, it is not environmental friendly and is expensive.
PMMA (Polymethyl Methacrylate):
PMMA, also known as acrylic, is also a transparent thermoplastic just like PC. Despite its basic properties of high transmittance (PMMA:92%, PC:89%) and high scratch resistance, its low cost makes it a highly desirable and useful material for many optical applications. PMMA can be reshaped and recycled without any deterioration. It is naturally stable to UV light and does not turn yellowish over time. It is also suitable for laser cutting. However, factors such as water retention, low softening temperature (<80°C) and more brittle structure can be considered as main disadvantages compared to PC.
Silicone:
It is rather a new material that has some advantages over PC and PMMA, such as high resistance to ozone and UV light, non-degradation up to a high temperature of 150°C, high flexibility and impact resistance. It is resistant to acids, bases, solvents, chemicals, oils and water. Low viscosity makes micro-structural design possible. With its flexibility, detailed shapes and features such as optical surfaces, sharp edges and small radii can be applied very accurately. Due to all these advantages, the demand for silicone, instead of PMMA and PC, in optical materials used in outdoor products is increasing. In short, although silicone stands out as a suitable solution for all lighting applications, the height of production cost seems to be the most important obstacle that restricts its widespread use. We can suggest that choosing a type of PC lens that provides UV and water resistance (UL746C) in outdoor and industrial applications for impact and chemical resistance and higher temperature operation, and PMMA lenses for low cost and recycling in indoor applications will be the most appropriate choices at the moment.
