Certain examples involve lighting systems controlled based on gas concentration data received by a controller. For instance, a lighting system includes a first light fixture to illuminate a first space. The lighting system also includes at least one gas concentration sensor associated with the first space, and a first controller that receives gas concentration data from the at least one gas concentration sensor. The first controller also overrides the illumination state of the first light fixture based on the gas concentration data received from the at least one gas concentration sensor by controlling the first light fixture in an alert state that is different from the illumination state.