Runway lights are used at night or during low-visibility conditions. That’s why not all the airports are equipped with the whole “package" of lights. For instance, St. Thomas Airport has only the basic edge lights because there is usually a beautiful weather in this area, which provides an excellent visibility. In turn, San Francisco Airport requires a full equipment of runway lighting as there are often low-visibility conditions. Runway lights consist of edge lights, threshold lights and runway end lights, threshold identification lights and runway centerline lights. All of these lights are have a specific color, type (flashing, constant) and intensity. Additionally, a runway is equipped with lights navigating an aircraft to the approach path, VASI (Visual Approach Slope Indicator System) or – a more popular and precise solution – PAPI (Precision Approach Path Indicator).