What LUX rating should backup lighting provide?

Emergency lighting should provide at least 10% of the normal lighting level according to BS5266 Part 1: 1999 and a minimum of 15 Lux. The Lux rating is commonly referred to as ‘illuminance’ or ‘illumination’ and is a standardised unit of measurement where 1 lux is equal to the illumination of a one metre square surface that is one metre away from a single candle.