Transmission Rates for Sunglasses - What are they?

Transmission rates. An unfortunate name for this part of the unending technology you can learn about sunglasses. This one is quite simple actually. It is what it sounds like. The transmission rate (also called transmittance) is a percentage given which describes the amount (or rate) 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). All lenses fall somewhere in between there, most being closer to 0%. Each different range of transmission rates also has categories which are organized like this:

Category 0: 80 – 100%
Category 1: 46 – 79 %
Category 2: 18 – 45 %
Category 3: 8 – 17 %
Category 4: 3 – 8 %

I hope this makes sense to someone

Category 0: These lenses are those which allow the most sunlight in and are commonly associated with safety goggles or eyeglasses, or when you need to be completely seeing what you are doing. Other colors in this range are bright yellow and some oranges. They are not really useful in sporting except for night time sports and indoor sports.

Category 1 lenses are more common. They can be used for most sporting events, as they will provide adequate coverage in most conditions.

Category 2 lenses are a lot more common and better suited for sports as they do not allow too much sunlight in as to affect your vision, but allow enough in to let you see what you are doing. Most brands use category 3 lenses for a large percentage of their models as this amount of light just happens to suit sports perfectly.

Category 3 lenses are quite dark. They are used for many different sports, where the light is so bright that you need extra coverage (e.g., snowboarding, skiing). They can be great for a day at the beach as well, and I would recommend them for many sports in daylight. Category 2 and 3 are the most common for everything from sporting to fashion.

Category 4 lenses are so dark that less than 10% of sunlight passes through them. You cannot see the eyes of the person wearing these kinds of lenses, so they are the dark kind the mustached-pervs wear in the park. Kidding. They are designed for conditions in which the sun will be beaming down on you. Some sporting events might require these kinds of shades, but usually they are for fashion, coverage at the beach, or to hide bloodshot eyes from your boss or clergyman. You CANNOT wear them while driving. It is not safe and is in fact illegal in many countries. Ok, enough lecturing for today.

Source: My Brain