Aviation tips: visual approach indicators. The visual approach slope indicator is a system of lights on the side of an airport runway sill that gives visual descent guidance information during approach. Many runways have visual glide slope indicators to help pilots. These lights may be visible from up to 8 kilometers (5 miles) during the day and up to 32 kilometers (20 miles) or more at night.

Basic visual approach slope indicators compose of one set of lights set up some 7 meters (23 ft) from the beginning of the runway. Every light is designed so that it seems as either white or red, depending on the corner at which it is viewed. When the pilot is approaching the lights at the correct angle, indicating the pilot is on the glide slope, the first set of lights appears white and the second set appears red. When both sets shows white, the aircraft is too high, and when both appear red it is too low. Everything you need to know is in this video: