Those red and white lights beside US runways tell pilots if they're coming in too high or too low; seeing 2 red and 2 white means the approach is on target

Pilots rely on Precision Approach Path Indicator (PAPI) lights that signal their approach altitude accurately. These lights enhance landing safety by indicating whether an aircraft is above, below, or on the correct glide path. PAPI is visible from about five miles during the day and can reach up to twenty miles at night. While PAPI assists with altitude, side-to-side guidance must be managed using the runway lights.