OK, First familurize yourself with the camcreate command.
This command is basically a way to create anything you want anywhere at any time. Very useful.
So, using camcreate we must create a flare to illuminate the area.
Flare = "Flare" camcreate (getpos GL1 select 0, getpos GL1 select 1, getpos GL1 select 2,55)
Put this in a script or trigger signalling when you want illumination. (For example on a radio command)
Basically, a flare will be created 55meters above a unit called GL1. (A game logic preferabley as they cant be seen but any unit will suffice.)
Any more Q's about this?