The unit used a solid state switching circuit and a special cell, which senses light through the window, depending on the position of the lens ring. The ring also allows the window to be partially closed. This lets you adjust direction as sensitivity. The ideal setting lets in enough light to activate the unit but yet reduces unwanted reflection. With daylight sensor, on at dusk, off at dawn-lets saving your energy. Provide safety-lets your home with someone living looks during vacation.