The current system works with light sources and occluder objects (to create shadows). You place lights and give them a radius and you place occluder objects where you want to block light. The shadow system renders the entire scene dark except for where there are lights or where light is blocked. You can control ambient darkness with a single global variable that makes the entire scene lighter or darker, and I've included a day/night cycle variable to help with this.
And yes, turning off the system is easy: you simply disable the light renderer and the room will be unlit.