We have just had the emergency lighting at our premises tested in house (small system). Most of the lights were fine, but a couple were not at full brightness at the end of 3 hours. So the lights were functioning, but only at say 25% capacity after the full 3 hours. Is this acceptable, as they were still lit, do they all need to still be at full brightness? 

They need to meet the minimum lighting level for the area - e.g. 1 lux on escape routes, 0.5 lux for open areas, etc.