Sunglasses For Sport sell a wide range of Category 4 sunglasses – probably the largest selection available in the UK. But what are they and where are they used? They are ideal for activities like skiing, mountain climbing, high altitude hiking and desert trekking: conditions where high glare or intense sunlight is experienced. Category 4 lenses are also suitable for eyes that are sensitive to bright light, a condition called photophobia. It’s a common symptom that’s associated with several different conditions, ranging from minor irritations to serious medical emergencies. Can Category 4 sunglasses be used when driving The lens tint category number for eyewear equates to a percentage of the VLT (Visible Light Transmission) – basically how much light the lens lets through, as follows: