I would not go so far as to assume the egress "emergency" lighting as "Optional". Generally these are a requirement of building codes.
There are conditions that the simple exit and and associated egress light (typical flood type) also would not be enough. Warehouses, large stores, etc that might require additional lighting for pathway egress maneuvering. There are troughers that also provide battery backup that are often used in such situations. Building code usually will include minimum egress lighting requirements in the form of "minimum candle power" at pathway. If you don't have these codes try contacting the building codes AHJ for their requirements in your municipality.
Fred, let’s say it’s determined the system is optional standby does this preclude the requirement for 90 minute backup battery in the exit signs as per NFPA 101? Could it be reduced to 60 min or 30 minutes?
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