I carry a pair of cheap amber colored Polaroids in my vest or backpack. I use them on low light overcast days, or with the early evening glare (esp. in the West), they are JUST AS EFFECTIVE under certain conditions as the grey lens are on bright days. Bill Dance and/or Jimmy Houston recommended them for certain light conditions for the hardware tossers on their TV programs. I tried it and it helps me
A Suggestion-- I hardly ever fly fish without wearing some type of eye protection. I feel naked without it. My dentist who flyfishes showed me a picture of a fly in a person's eyeball.