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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 

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] 

## Runway Lighting 

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) 

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. 

## Runway Edge Lights 

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 

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