Hi,
To do this,
1) Find the number of the buoy you want to add the light to (from the buoy.ini file)
2) In the light.ini file, add the light by:
Increasing the 'Number=' value by one, and then adding a section in the following format:
Buoy(#)=<Buoy Number>
Height(#)=4.0
Red(#)=255
Green(#)=0
Blue(#)=0
Range(#)=4.0
Sequence(#)="LLDDDDDD"
StartAngle(#)=0
EndAngle(#)=360
Replace the '#' with the number of the light, and <Buoy Number> with the number of the buoy you want to add the light to. This example would add a flashing red light, on for 0.5s, then off for 1.5s, and at 4m above water level.
For more details, have a look at https://www.bridgecommand.co.uk/Doc/WorldFileSpec.php