Maya 3-d modeling dark spots with clean geometry?

sometimes when i model in maya, dark spots appear on the surface. this has noting to do with textures its all about geometry. when i create a low poly object and smooth it, sometimes the dark ring appears along edgeloops on certain spots of the model. i dont understand its annoying. is there something that isnt clean on my model? the model is all quads, all the vertices are joined together where the edgeloops appear. the quads are not twisted up either where it seems like it'll need to be defined by a simpler polygon