Obviously one of the main requirements of any decent pair of sunglasses – whether Matrix sunglasses or some other type – is that they protect your eyes from excessive light. Light is generally categorized in terms of visible and invisible light, and the two types of light that tend to produce the most eye discomfort are UV rays and glare.
Visible light is that which can be seen by the naked eye. In terms of visible light, red contains the lowest amount of energy and violet the most. In terms of invisible light, ultraviolet or UV light has a lot of energy, and sunlight happens to contain tons of UV light. These UV rays can be particularly damaging to corneas and retinas. That is why quality sunglasses are specifically designed to protect your eyes from the harmful UV rays of the sun.
Another type of light that sunglasses help mitigate is glare. This essentially refers to the brightness of light, especially as it bounces off of reflective horizontal surfaces like the ocean or a road, and it is measured in something called lumens. Whenever the brightness of the light exceeds 4,000 lumens, our eyes cannot effectively filter it all out and we see white flashes. It is these white flashes that are symptomatic of glare, which inevitably leads to squinting and discomfort or headaches. The main attribute of sunglasses that helps mitigate the effect of glare is polarization.
Just for some perspective, a regular indoor light might be around 500 lumens, bright sunshine reflecting off of cement might be around 5,000 lumens, and bright light reflecting off a snow field might be around 11,000 lumens! As I’ve already said, our eyes can deal with this until we reach about 4,000 lumens, so you can see the need for polarized sunglasses in certain situations like fishing, skiing, or driving to name a few.
To sum it up, at the bare minimum your shades must protect your eyes from the UV rays of the sun. And if you spend a lot of time outside on large horizontal surfaces, get sunglasses that are polarized as well.