At best, a lightbar can "SUPPLEMENT" markers on a planter, but a lightbar will "NOT" replace markers.  IF you want to replace the markers, you will have to go to some kind of assisted steering.  Lightbars have their place and work well is some applications.  Planting is not one of them.  Most lightbars have 1' accuracy at best, even then you will be "chasing the lights".  A lightbar will help in conditions where the mark is hard to find or see.  It will get you in the general area you need to be looking for the mark at.

As others have suggested look at a system that can be upgraded to assisted steering.