is there any possible way that when a character walks over a section that is being lit from a light on the roof, that it sets off an alarm or some animations?
For my stealth game, I accomplished this by putting triggers in every single area of significant light (actually in my game I had a bigger trigger with a smaller trigger inside... the smaller trigger was high light, the bigger one around it was low light, as I wanted a gradient effect and a stealth meter). There's unfortunately no "easy" way to accomplish what you're trying to do in Unity, since there's no way (that I know of) to "grab" how much light is being shed onto your character. If there was, I would have done it in a heartbeat. :)