Just primed my basement walls after sheetrock was compounded and sanded thoroughly and smooth as silk. only have 4 pull chain lights(just light bulb hangin down) at this point and certain areas of room light shines down and i can see joint line from top to bottom in various areas. I understand the sanded joint compound is shinier and primer didnt seep into it like the wallboard thus the shadowing. bought premium flat paint to finish walls./will this cover these areas and eliminate/ cover the shadows?
Welcome Duck, flat would be the best option for hiding imperfections. However, shadows are created by light going across an imperfect surface. As good as your seams may be, they are still an irregularity on the surface, and they aren't going to fool the light. Coat it out and see what you've got. What else can you do at this point? You may find they disappear completely or at least become something you can live with or mask some other way.