What lighting specification should I use when planning a lighting installation?
It is usual for contracts to refer to a lighting specification, in which case the lighting specification may be a contractual requirement.

If there was no specification referred to in a contract, a lighting planner would owe a duty of care to the client to use in order of priority:
Harmonised Euro Norms (e.g. EN 12464)
National Standards
Local guidance notes (e.g. HSG 38)
A lighting planner would have to demonstrate a good reason to deviate from this order of priority.

e.g. corridor lighting

Harmonised Euro Norm - EN 12464 - Clause 5.1.1. Corridors - Em 100 lux / U0 0.4 / UGRL 28 / Ra 40
Local guidance note - HSG 38 - Corridors - 20 lux average illuminance / 5 lux minimum measured illuminance
HSE's Lighting at Work booklet (HSG 38) allows a much lower lighting level than EN 12464, but HSG 38 is 2 steps below EN 12464 in the order of priority. You would have to have a good reason not to comply with EN12464. http://www.healthandsafetyatwork.com/hsw/content/making-light-work (opens in a new window)"