Red and green are used for normal vector rescaling - see PluginsAndObjects for more info. Blue and alpha are used to create the top and bottom angles - blue is the number of degrees above heading to change colors, alpha is the number of degrees below.
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).
This VASI has a viewing angle - if viewed too far above or below angle, based on the blue and alpha params, the texture coordinates are moved (to the left if viewing below) and right (if viewing above).
This allows you to make a tri-color VASI like on the frigate.