@mattfee63704 that'll depend on how dark is dark. If you can, and if the picture is not to dark ;) post some pictures of it with your Question. That way we can see what you see.
Vizio TV's are not the highest quality when it comes to their parts. It's more of a hodgepodge of parts. It could be that the backlight LED's are starting to fail or that the power board does not provide enough power to them.
Neither one of those things is terribly complicated to fix but the backlight LED's are more of a PITA because of the panel size. To figure out if you have the proper voltages for your back lights, you will need some basic hand tools in order to remove the back cover. Then you need to take more pictures. This time of the circuit boards, and post those as well. We can then point out where to measure and what approximate voltages you should get.