The experimental electron density analysis is becoming a very mature field of research with outstanding applications in many areas of solid state physics and chemistry. This approach has allowed gaining new insights on bonding interactions in ground state systems often from joined experimental and theoretical methods. The extension of this technique to out of equilibrium systems is very promising and might surely lead to a better fundamental understanding of dynamic processes in solids such as phase transition or chemical reactivity [1]. Steady-state and time resolved x-ray diffraction techniques under external perturbation, like electric field [2], pressure or optical excitation [3], are more and more developed, mainly for structural purposes. We have shown that under appropriate and well controlled experimental conditions, accurate electron density distribution of metastable states can be derived [4]. State of the art in light-induced high resolution x-ray diffraction experiments and charge density analysis of molecular metastable states will be presented. Applications will cover light-induced phase transitions in Fe(II) spin-crossover complexes and solid state chemical reactivity.