Realistically speaking, the chances of actually getting into any serious trouble are probably quite low. Most of the time, law enforcement officers have more pressing issues to deal with during mass demonstrations than individual cases of lights being turned off. As long as the protesters can avoid being directly linked to any damage caused (e.g., broken windows, etc.), they're unlikely to face any major legal backlash. In the end, it's all about raising awareness and starting a conversation – and it seems like this particular tactic has been successful in achieving that.