Is old but useful thank you!,but right now im dealing with the very same problems of bad lighting in my imposters (using 4.8) i already double check everything and still having broken lighting (objects look black from one angle and completely white from another) , is there any change in 4.8 to be aware of? than you!
EDIT: ha, just found out my what my problem was… i didn´t notice the “-” symbol in the 0.5 value for remapping for the normal map texture… my bad 