How can improve the illumination and brightness of led pod lights by adjusting the refractive index of PC len

It is much complicated to improve the lighting performance of LED pod light by adjusting the refractive index of pc optical lens. Engineers have aimed to bridge the refractive index gap between the led chip and the surrounding air. In doing so, they can reduce total internal reflection and fresnel reflection losses greatly by increasing the refractive index of the PC optical lens to that of the LED die.

Common LED chips have a high refractive index . Standard Polycarbonate has an RI of approximately 1.58.4 When light moves from the LED chip to the optical lens and then to the air (5$n = 1.0$), much of it hits the boundary at a steep angle and reflects back inward instead of escaping.

By raising the refractive index of the PC  optical lens towards 1.65–1.75, you widen the "escape cone" of the light beams.

While you cannot easily change the refractive index of a molded optical lens, manufacturers adjust it during the material formulation stage by two said solutions of high- refractive index additives or high- refractive index nanoparticles. Adding sulfur-containing compounds (polythiols) is a common industrial method to push refractive index of optical len above 1.60. Incorporating brominated or chlorinated monomers can raise refractive index, though this is sometimes prohibited by some environmental regulations. Nanocomposite doping is another latest approach where the optical matrix is infused with metal-oxide nanoparticles that have extremely high refractive index. The metal-oxide particles must be smaller than the wavelength of the light typically below <40nm to prevent scattering, which would make the optical lens look cloudy.

Instead of changing the whole optical lens, you can apply a coating that acts as a bridge.By layering materials so the refractive index gradually transitions from 1.58  to 1.0, you can eliminate the abrupt interface that causes reflections.

It is not just an “easy and free” upgrade on the optical lens by adjusting the refractive index. You need to make a balanced consideration between dispersion and transmittance of light beams. When you increase the refractive index of optical len, the abbe number usually drops. This results in higher color fringing around the edges of light beam.Higher refractive index can sometimes move "absorption edge" into the visible spectrum, so the light beam may look little yellowish. Also, specialized high refractive index polycarbonate resins are more expensive than standard PC optics.