In an open - loop system , the photosensor detects the amount of available daylight only .
In an open - loop system , the photosensor can be positioned on the building 's exterior wall or roof , or inside the building facing the window or skylight .
In an open - loop system , the photosensor detects the amount of available daylight only , and can be positioned on the building 's exterior wall or roof , or inside the building facing the window or skylight .