Red and green are used for normal vector rescaling - see PluginsAndObjects for more info. Blue and alpha are ignored.
RGB color is set to white. Alpha is set to brightness or 0 for off. Texture coordinates may be modified.
This light turns off when VASIs are inoperative.
This light requires the object sequence number to be an elevation angle for the VASI to change colors.
The VASI light modulates its brightness based on the angle the user looks at it -- it will go dim if viewed too far off angle above, below, left or right. The RG components rescale the normal. The "direction" of this light is always along the Z axis (subject to animation).
The VASI is being viewed below the viewing angle (object sequence number) the texture coordinates are modified, being moved to the right by the width of the light.