Emergency lighting is self-explanatory and refers to illumination used in an emergency when the main power source fails. A fire or a power outage could result in the loss of mains energy, causing the typical lighting supplies to fail. This could result in unexpected darkness and a threat to the residents physically and can cause panic. 

Emergency lighting is typically required to run entirely automatically and provide adequate illumination to allow people of all ages to safely exit the premises. Most new buildings today have emergency lighting added during construction, with the design and type of equipment often chosen by the local authority, architect, or consultant.