What is the minimum emergency lighting required when normal lighting fails?

When considering the minimum emergency lighting required during a failure of normal lighting, the correct answer of 1 foot candle aligns with established safety standards, particularly those set by the National Fire Protection Association (NFPA) and similar codes.

The requirement of 1 foot candle reflects a balance between providing adequate illumination for safe evacuation and ensuring energy efficiency. It is often specified as a minimum level of illumination to be achieved in exit paths, at stairs, and in areas where people may need to be directed to safety. This level of light is sufficient for occupants to identify exits and navigate spaces without experiencing significant disorientation or panic.

The other levels of illumination mentioned are above the minimum standard, which could lead to unnecessary energy consumption in emergency lighting systems, without providing commensurate benefits in terms of safety. Standards often prioritize just enough light to enable safe egress without excessive illumination that could contribute to higher operational costs or complicate installation requirements.