Thanks for the quick reply ICE.
Note the exception for dwelling and sleeping units. Note that auditoriums, theaters, concert or opera halls and similar assembly occupancies are allowed to dim the lights. Clearly your second option is the correct choice.
I had deliberately left out the exceptions from my question because they were irrelevant to my specific use case, but you're right that their wording strongly suggests interpretation #2.
As far as definitions go, I do of course agree that the MoE begins at any occupied portion, but my question was about "serving" (i.e., can a portion of the MoE serve a room, or does the entire MoE serve the room). Since the Code doesn't seem to emphasize this distinction anywhere else (whereas it is very clear, for example, about the three different parts of the MoE), I think interpretation #2 is likely correct as you say. The same way if you refer to "all the HVAC ductwork serving a specific room", this would include any ductwork in the room itself.
As to a classroom, my experience has been that not all of the lights were turned off. I have no experience with a darkroom but there must be some light or Jeff would spill his coffee and crash something.
I feel like it's not difficult to come up with scenarios of Group E, Group F, or Group I occupancies which require (non-sleeping) people occupying a space in complete darkness. Not too long ago, it wasn't unusual to have darkrooms in American high schools. And yes, a darkroom does require (for at least a small part of the development process) complete darkness (otherwise you would ruin the exposure). There are many other chemical processes (found in laboratory, educational, manufacturing, or healthcare environments) which are similarly light sensitive.
Another issue is that conventional units of illuminance are based upon the photopic luminosity response. But it's possible for some spaces (again darkrooms for a portion of the development process) to use low levels of red light (producing less than 11 photopic lux at the floor), which nevertheless allow an average sighted person to function as well as if it were 11 lux (once their eyes adjust from the photopic regime to the scotopic regime). That is, you can create a situation with 11 scotpic lux at floor level, but less than 11 photopic lux.
But here’s the thing about this. I am just an inspector….. I am not an authority on the subject. Wait for the heavy hitters in the plan check realm before you run with it.
I guess my only remaining reservation is that it just feels weird to completely prohibit an occupant from turning off all the lights in a space, especially when there are plenty of (niche, but not unfamiliar) use cases where this is essential.
