VIOFO CPL For A119S / A129 / A129 Duo Front & Rear Dash Camera The CPL (Circular Polarizing Lens) can be used to reduce reflections and glare from the window glass and road surfaces that can otherwise damage image quality, this works in the same way as polarized sunglasses. With our exclusive designed CPL filter, it could further reduce the reflections from windshield, getting more saturated and beautiful video.