The only powerfull lightbeam I know about in freeware is the one which is embedded in that luxury boat addon.
You can find more details in that topic:
http://www.sim-outhouse.com/sohforum...g-light-effect
Perhaps you can edit that effect to change the angle of the beam ?
It's just a 3D beam though. It does not illuminate the ground. But seeing the ground through the beam makes it look clearer, as if it were illuminated, kind of :P
Here is how it looks like by default, when I attached it in the front of the Merlin:
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