I have PC prescription glasses. (They may be by design less sensitive and/or dark than sports PC sunglasses so they stay fully clear indoors)

My experience in using them cycling is they don't get enough UV from the sun to change when the sun is low in the horizon. That is also when its nice to have them dark if you are riding into the sun.

I find them most effective on cloudy/overcast days when there is a lot of scattered UV. On clear days the sun is simply too bright and they don't get dark enough.

What I mean by this is when there is sunrise/set and I look towards sun they barely dim. When it is overcast during midday and to my eyeballs feels much less bright than looking into the sun they get quite dark.

Al