Collision detect no physics / colliders (FogOfWar)

Hey I'm making fog of war script and unity tells me that I have to many colliders or rigidbodies in the scene so i try to make it works without physics or colliders

the fog of war is cubes - the cubes are static so I have load there positions into one big list.

Untill now i done it with sphere cast how to do it now?

Please help!