Silicone materials are preferable to traditional polymers in high-intensity LEDs, according to Dow. The firm say silicone offers high transparency in the UV and visible region, refractive index controllable over a wide range, and particularly stable thermo-opto-mechanical properties. Materials currently in common use for closely-coupled LED optics, such as PMMA, PMMI and PC , are reaching their thermal and optical limits with the increasing radiation density and power of LEDs, particularly white ones. The high temperatures and UV content near the chip cause cracking of chemical bonds, resulting in yellowing of the material which reduces the transparency. Typically, once this degradation process has started, it accelerates itself due to the increased energy absorption, resulting in rapid failure of the optical system. The higher the performance of the LEDs and the closer the optic is attached to the die — which is desired to achieve better efficiency — the higher is the probability that this degradation occurs. The new silicone materials’ higher optical and thermal performance overcomes these limitations, and Dow say the silicone can be cured to a resilient physical modulus that offers shockproofing to the finished assembly.