True, a category 3 and of course 3.5 etc is needed
: Those who need sunglasses but require corrective vision.
I am fortunate that I can go around (travel/ sight see etc) without corrective vision. I do however have glasses for driving at night or seeing a stage production, a movie, whatever is far away etc. I bring them when I travel in case I need them.
From what I have seen, most clip or magnetic clips that come with glasses feature a polycarbonate lens. The entire thing is "OK" in my humble opinion. But like most things that are "dual Purpose", they rarely do both tasks well.The quality of the dark clip-on leaves much to be desired. Those who are thinking of this option, I reccommend you consider the following. Have 1 pair of "clear" glasses and 1 pair of tinted that you will use as sunglasses. This way you can choose the color and darkness of the tint that you want. Now I know this may be prohibitively expensive...One money saving tip is to try to supply the frames for both pairs.
Look for frames at the above-mentioned department stores. You will pay ~$20 for the frame instead of ~$200!!!
Try to get ones that have screws that allow the removal of the lens (in the case of metal frames). Plastic frames are just a "snap-fit". I like the half frames. The ones that have metal on top and no frame on the bottom. The lens is held in place with a thin nylon line. In either case, always keep the original lens that comes with the frames. It can be used by the optical dispenser as a template for cutting your prescription lens.
Difficult prescriptions (High + or High -)will always be more diffcult to fit into frames. Most other who have "Plug and Play" prescriptions should find the above tip useful.
A couple more thoughts:
Polarized lenses do need time getting used to. They are great around the water but some people find driving with them difficult as they tend to highlight prismatic reflections in windshields and glass.
Photo-chromatic (automatic color darkening) lenses are great for most applications BUT will not fully darken when driving. The lenses are activated by UV and glass filters out most of the UV.
Dark Grey lenses are the least desireable, someone mentioned above that they are depressing, I think so too. I find them too dark and furthermore, some tones of grey take away from the true colors of nature.
Good luck!!