Visual Approach Slope Indicator (VASI) is the most common visual glidepath system. VASI consists of lights arranged in bars that are either 2-bar or 3-bar systems. The 2-bar VASI has near and far light bars and the 3-bar VASI has near, middle and far light bars. The principle of VASI is to provide a colour differentiation between red and white to help indicate that you are on the correct glidepath.
Precision Approach Path Indicator (PAPI) system. PAPI uses lights similar to that of the VASI system, except they are installed in a single row, normally on the left side of the runway. PAPI, like VASI, provide only one visual glidepath that is normally set at 3°.