First, look at a photo, or a landscape and try to guess which note in the system you should use. Then put these on and you'll find how your eyes trick you.
I paint all my note paintings wearing these, and then I don't have to hold anything. Once I started painting with them I don't want to paint without them.
Once you look through these, you may be surprised how far off your perceived value notes were!
You'll want a pair for the studio and another if you paint outside.
Also, they offer 100% UV protection.