According to ASHRAE 90.1, section „g. Stairwell Lighting – Lighting in stairwells shall have one or more control devices to automaticcly reduce lighting power in any one controlled zone by at least 50% within 30min of all occupants leaving that controlled zone.” Can anyone tell me what is the definition of a controlled zone in a stairwell? Is it acceptable that the lightning is controlled automaticly but in the whole stairwell without dividing it into a few zones?