I have done some testing of this wanting to build a lighthouse myself and the main problem I find is not the brightness of the light source but the render distance the game limits. My last build was with bonfires and even with those on raised surfaces I could at best see the fire render at max of about 100 yards, maybe even less.

I suppose it comes down to what you want to get out of a lighthouse, if you are going for something that you can see from a far distance you will be disappointed as things are now.

I would be curious if anyone has had a better experience with this or have been able to see fires at longer render distances perhaps it could be just my pc/settings.