I am scripting an elevator and because of crappy lighting system I have two choices: no light inside the elevator or light clipping outside the elevator. BUT there may be another way - if someone looks inside the elevator, the light will locally activate for the player that looks on it. But how- no, is it possible to do that?
If you want to see if it is at all visible from the player's camera, try: http://wiki.roblox.com/index.php?title=API:Class/Camera/WorldToScreenPoint
I'm not sure but you might be able to do it by placing an invisible, collisionless part over the entrance of the elevator and use the mouse hover enter function (https://wiki.roblox.com/index.php?title=API:Class/ClickDetector/MouseHoverEnter)?
That is not possible, im afraid.