The transmission rate is a percentage given which describes the amount of sunlight that will go through the lenses of your sunglasses and into your eyes.
Being a percentage, they run from: 0% (black as night) to 100% (clear as day).
Category 0: 80 – 100% - Clear Comfort / Light Enhancing
Category 1: 46 – 79 % - Weak Sunlight
Category 2: 18 – 45 % - Average Sunlight
Category 3: 8 – 17 % - Strong Sunlight
Category 4: 3 – 8 % - Exceptionally Strong Sunlight. Not suitable for drivers and road users.