The term "isodynes" has been proposed by Pindera and Mazurkiewicz to denote a new family of characteristic lines of plane stress fields. These lines carry information on total normal forces acting on related cross sections and yield the distribution and values of related normal and shear stress components. Two families of isodynes related to two characteristic directions yield the values of all three components of a plane stress field and additional redundant information. Isodyne photoelasticity methods can be applied to determine all three stress components in photoelastic models and in original machine or structural parts using isodyne coatings. The term "gradient photoelasticity" has been proposed by Pindera and Hecker to denote a new method of photoelasticity which utilizes relationships between the curvature of light paths in a photoelastic object and the gradients of symmetrical and distortional parts of stress/strain tensors. Utilizing a basic mathematical model of photoelastic effect presented by Ramachandran and Ramaseshan, gradient photoelasticity yields the momentary values of absolute and relative photoelastic coefficients. Both methods can be applied to determine the values of stress intensity factors for arbitrary cracks and all stress components in composite structures.