If I read this correctly, ground fault indicating _lights_ are not required, just some sort of ground fault detector.
IMHO ground fault indicating lights are the _simplest_ and least expensive form of ground fault detector that one could use.
But if a facility had a different sort of ground fault detector, then that would probably meet the requirements of the code.
Ungrounded systems are usually used for continuity of service. But what about an ungrounded system used for the purpose of reducing energy dissipated in a fault. If the breakers were arranged to detect and trip on a ground fault for an _ungrounded_ system, then IMHO this would meet the requirements of having a ground fault detector.
One could imagine a system that used coordinated ground fault detection so that the breaker nearest the fault would trip, at the same time never having large ground fault currents flowing.
-Jon
