Failure prediction in sheet metal forming is presently mainly based on experimentally measured Forming Limit Curves. The latter characterize formability limits in a technical sense but they do not deliver any information about the physical phenomenon of failure by fracture. The present contribution aims to propose a new approach in interpreting FLC’s, based on an accurate experimental analysis of localization phenomena. The width of the localization band is now considered to be a key indicator of the localization level reached by the material. Two alternative procedures, based on the optical measurement of the strain distribution and strain rates of Nakajima samples, will be detailed for the evaluation of the method. The paper hints furthermore to the possibility of measuring the actual strain at failure, again using the optically measured Nakajima strain histories. The forming limit diagrams, now representing the different levels of localization from the beginning of deformation until occurrence of fracture, will now be designated as Localization Level Forming Limit Diagrams (LL-FLD). The contribution will close with some examples for an LL-FLD based evaluation of process behavior.