Obstruction lighting should be visually observed at least once each 24 hours, or checked by observing an automatic and properly maintained indicator designed to register any failure of such lights, to insure that all such lights are functioning properly as required. In the event the obstruction lighting is not readily accessible for the above observation at least once each 24 hours, an automatic alarm system designed to detect any failure of such lights may be installed to replace the normally required visual inspection. The commission will not object to excluding the side or intermediate obstruction lights on an obstruction from the alarm circuit, provided the signaling device will indicate malfunctioning of all flashing and rotating beacons regardless of their position on the obstruction, and of all top lights; and that all obstruction lights mounted on the obstruction are visually inspected at least once every two weeks, with all lamps being replaced at regular intervals after being lighted the equivalent of not more then 75 percent of their normal life expectancy.