During a fire emergency or power outage, employees, customers and tenants must be able to find the nearest exit quickly. If areas of your building have no natural lighting then occupants could be at risk in an emergency.
Emergency lighting provision forms part of your Fire Risk Assessment (FRA) It is a legal requirement that emergency routes and exits requiring illumination must be provided with emergency lighting of adequate intensity in the case of failure of their normal lighting.
BS5266 part 1, requires that emergency lighting systems are able to provide light for 3 hours following the loss of mains power.