The general question is: How does line of sight and blinding conditions affect area spells?
- Can I target the point of origin of an area spell, like fireball, in a zone where I do not see, a dark room or a zone affected by a darkness spell?
- If I play with a square grid, am I allowed to pick exactly the point of origin on the mat?
In my opinion picking the point requires precision which would require at least a perception roll, but the rules are not clear on this.
- Is there any kind of penalty for a blind caster casting an area of effect spell (like there is for spells that require an attack roll)?
The only relevant paragraph I found on the PHB is "A Clear Path to the Target" which does not answer my question.