One non-conservative scenario is an imagined situation in which the laws of physics change over time: a changing gravitation constant could be used to extract energy from 'nothing' (or lose energy to 'nothing'). read more
Conservation of Energy was shown by Noether's Theorem to be a very real law of physics. It is a consequence of the fact that the laws of physics do not change with time. If the laws of physics did change with time, we could extract free energy. read more
Law of conservation of energy states that, Energy in the isolated system remains constant. Now, for the conversions you have provided, light energy is nothing but collection of electromagnetic waves. These waves carry energy proportional to their frequency. Light gets reflected, transmitted or absorbed. read more