Sunglass categories range from 0-4 tint and refers to the amount of visible light the lens absorbs. Categories 2-3 are the most popular with 2 for shopping or cloudy days etc. and 3 for beach and driving in bright sunlight.
0 very light- 0–10%. This offers no to very mild tinting, and so absorbs very little visible sunlight. This means category 0 glasses aren’t actually sunglasses. Standard prescription glasses that are clear fall into category 0.
1 light- 10–20%. Although these absorb more visible sunlight than category 0 glasses, they still aren’t that helpful on sunny days. They are most often worn on low-sun or overcast days by people with sensitive eyes. Consequently, these don’t count as sunglasses either.
2 medium- 20–43%. The tint on these lenses is obvious and clearly marks them out as what most people would view as sunglasses. They’re ideal for overcast to moderately sunny days.
3 dark- 43–80%. The ideal sunglasses for playing outdoor sports or enjoying sunny days when the sky is clear use category 3 lenses. Category 3 sunglasses are the ones you’ll take on holiday, to the beach or for everyday use if you’re lucky enough to live where the sun is most often always shining brightly.
4 very dark- 80–92%. This means most visible sunlight is absorbed. Sunglasses with category 4 lenses are, therefore, not your everyday-use sunglasses. They are used for extreme sun exposure days, such as if you go skiing and are very dark to peer through.
