the Polarflite Tipsi Lens Colour determines how much light will pass through a lens. To keep vision optimal, you need less light in sunny conditions and more in cloudy weather. the Brown Lens has a superb all-round constant density lens. It provides the best combination of true colour transmission and contrast. The optimal performance is achieved in medium bright to bright conditions. The Yellow lens works as a light enhancer. Good for dusk and low light as well as for overcast days and evenings.