There are many views on this, high risk area emergency lighting is probably the only type of emergency lighting where a definition of the time required to maintain the light is mentioned. Basically it says that it has to "kick in" within 0.5 seconds and maintain 10% of the normal lighting for as long as the hazard requires to be safely shut down.
So if it takes 5 minutes to shut down a machine for example then the requirement is that the light should remain on for at least that length of time.
Now in the test procedures we have to do a full 3 hour run down to test the battery packs for say open area lighting and fail those that do not achieve the full 3 hours. I have just tested a building where the fire plan and evacuation is around two minutes, in my view as long as people are evacuated safely I really do not see the problem. However it is not my call so I fail all those that do not achieve the full 3 hour run down.
