With a comfortable fit and spherical lens, the Boa remains popular year on year, offering all the essential features you need enjoy your time in the mountains. Designed to fit medium to large faces.Lens: Light Purple Mirror SilverVLT: 13% (CAT 3)Size: Medium/Large Lens Shape: SphericalLensLight Purple Mirror Silver – With a 12.6% VLT this lens is at its optimum in bright, sunny conditions.Visual Light Transmission (VLT) refers to the amount of light that penetrates a lens. A low percentage means less light passes through and a higher percentage lets an increased amount of light through. A lens with a lower VLT rating is better for bright conditions, where as one with a higher VLT is more suited for overcast and snowy days