Refer to figure.
ICAO Annex 14
5.3.4 Approach lighting systems

Simple approach lighting system
5.3.4.2 A simple approach lighting system shall consist of a row of lights on the extended centre line of the runway extending, whenever possible, over a distance of not less than 420 m from the threshold with a row of lights forming a crossbar 18 m or 30 m in length at a distance of 300 m from the threshold.

Precision approach category I lighting system
5.3.4.10 A precision approach category I lighting system shall consist of a row of lights on the extended centre line of the runway extending, wherever possible, over a distance of 900 m from the runway threshold with a row of lights forming a crossbar 30 m in length at a distance of 300 m from the runway threshold.

Precision approach category II and III lighting system
5.3.4.22 The approach lighting system shall consist of a row of lights on the extended centre line of the runway, extending, wherever possible, over a distance of 900 m from the runway threshold. In addition, the system shall have two side rows of lights, extending 270 m from the threshold, and two crossbars, one at 150 m and one at 300 m from the threshold, all as shown in Figure 5-14. Where the serviceability level of the approach lights specified as maintenance objectives in 10.5.7 can be demonstrated, the system may have two side rows of lights, extending 240 m from the threshold, and two crossbars, one at 150 m and one at 300 m from the threshold, all as shown in Figure 5-15.

Runway approach lighting systems can basically be divided into two main categories: Simple and Precision.

Precision systems are further subdivided into Category I and Category II/III types, depending on the operational requirements, but for exam purposes, the key distinction is generally between Simple and Precision systems.

Simple Approach Lighting System:
Usually installed on non-instrument or non-precision runways. The main purpose is to provide visual guidance to help the pilot identify the runway direction and threshold area; it consists of basic light patterns without complex arrangements.

Precision Approach Lighting System:
A more advanced setup, designed to meet the requirements of precision approach operations. Category I systems may also be used on non-precision runways, as they can still provide adequate guidance. Category II and III systems are specialized for low-visibility conditions (CAT II/III) and include denser light configurations and additional components for enhanced precision.

Note: Although approach types are non-precision (without vertical guidance) and precision (with vertical guidance), approach lighting systems are divided into simple and precision.