Required sources of natural light shall have an aggregate transmitting area of at least ten percent of the floor area of the room or space served and where an enclosed or partially enclosed balcony or space above a setback complying with section 27-733 of this article intervenes, the required sources of natural light shall have an aggregate transmitting area of at least ten percent of the combined floor area of such room and the portion of the balcony or space directly adjoining and in front of such room. Each required source shall have a minimum transmitting area of twelve square feet and only that area of the light source above thirty inches from the finished floor may be considered as providing the natural light required in any space.