The VASI (Visual Approach Slope Indicator) and the PAPI (Precision Approach Path Indicator) are systems of lights that provide guidance information to help pilots acquire and maintain the correct approach to an airfield. They are generally located beside the runway. These lights can be seen from up to 8 kilometers (5 miles) during the day and up to 32 kilometers (20 miles) or more at night. Further information is available in the video below: