If the sun comes out, fish deeper
Where other animals have eyelids they can squint, or pupils that can constrict to help block out bright light, trout do not. They can’t squint and their pupils don’t constrict.
Their eyes are adapted for lower light levels, so when it’s sunny, they don’t feel that comfortable and they’ll drop through the water layers to find deeper water where less light has penetrated. When the sun comes out, make sure that you change to fishing deeper, otherwise, the trout may miss your flies.