Hello,

I have a problem Im trying to apply blidness spell on an actor. I use fire&forget spell, magnitude 100, effect archetype: Value Modifier, assoc. item: blidness. Unfortunatelly the actor can still spot me and attack me. Anyone has any suggestion?

If they can hear you they will still attack. If you do not sneak they will hear you. It is unfortunate.
Also, if the spell itself will cause detection then they will know where you are until they 'lose you'.

There is a blind character in the game. You could take a look at him in the ck. His name is http://www.uesp.net/wiki/Skyrim:Ulfr_the_Blind.