All you want the AI to know is light hitting the thief, and is a straight line of sight available between the player & AI If it is true you could use the light gem. This is a far simpler way of getting that interaction from the AI. They are not going to go ooh look pretty gfx effect! Without light he would be invisible. But with bright/moderate light either behind or in front he would be illuminated, provided, say a wall is not in the way. This is not pedantic its fact, imagine standing the other side of the tunnel & the thief would be lit. If not then the quantity of the light coming down the tunnel is NOT enough for a sillhouette if you were then at the other end of the tunnel. Go outside and try it in RL. BTW I used to teach physics so don't bother arguing So you dont need additional complex calculations to test for his visability, in order to get the same game play effect. Just that for the light gem. Oh I read a bit from the oblivion devs they had life like bow physics in the game , but dumbed it down as it was not entertaining. Anyways GL ppl keep it up! I think your mod is a great piece of work I hope you finish it.