light. The “slightly below glidepath” indication is a steady red  light. If the aircraft descends further below the glidepath, the  red light starts to pulsate. The “above glidepath” indication  is a pulsating white light. The pulsating rate increases as the  aircraft gets further above or below the desired glideslope.  The useful range of the system is about four miles during the  day and up to ten miles at night.  [Figure 14-32]  There are various lights that identify parts of the runway  complex. These assist a pilot in safely making a takeoff or  landing during night operations.  Runway end identifier lights (REIL) are installed at many  airfields to provide rapid and positive identification of the  approach end of a particular runway. The system consists  of a pair of synchronized flashing lights located laterally  on each side of the runway threshold. REILs may be either  omnidirectional or unidirectional facing the approach area.  A tri-color system consists of a single-light unit projecting  a three-color visual approach path. Below the glidepath is  indicated by red, on the glidepath is indicated by green, and  above the glidepath is indicated by amber. When descending  below the glidepath, there is a small area of dark amber. Pilots  should not mistake this area for an “above the glidepath”  indication.  [Figure 14-31]  Pulsating VASIs normally consist of a single-light unit  projecting a two-color visual approach path into the final  approach area of the runway upon which the indicator is  installed. The “on glidepath” indication is a steady white  Runway edge lights are used to outline the edges of  runways at night or during low visibility conditions.  [Figure 14-33]  These lights are classified according to the  intensity they are capable of producing: high intensity runway  lights (HIRL), medium intensity runway lights (MIRL), and  Runway Lighting  Runway End Identifier Lights (REIL)  Runway Edge Lights  Figure 14-30.  Precision approach path indicator for a typical 3° glide slope.  Figure 14-31.  Tri-color visual approach slope indicator.  14-17  Below glidepath  Above glidepath On glidepath  Amber Red Green Amber  High  more than 3.5°  Slightly High  3.2°  On Glidepath  3°  Slightly Low  2.8°  Low  less than 2.5°  On Glidepath Below Glidepath  Above Glidepath  Far Bar  Near Bar  Far Bar  Near Bar  Far Bar  Near Bar  Figure 14-29.  Two-bar VASI system. 