The legal requirement for emergency lighting is that – “Emergency routes and exits requiring illumination must be provided with emergency lighting of adequate intensity in case the lighting fails”.
The law is explained and the rules for compliance are given in a the following HSE jointly issued document, “FIRE SAFETY – An employer’s guide”. Further details can be obtained by clicking on the following link http://www.archive.official-documents.co.uk/document/fire/
The Regulatory Reform (Fire Safety) Order 2005, section 9.—(1) states that:-
“The responsible person must make a suitable and sufficient assessment of the risks to which relevant persons are exposed for the purpose of identifying the general fire precautions he needs to take to comply with the requirements and prohibitions imposed on him by or under this Order”
Regulations on testing are covered by BS 5266 and this standard details the requirements for emergency lighting.
Those requirements state that emergency lighting systems should be periodically tested and inspected to ensure that all luminaries operate correctly in main power loss situations.