Consider Einstein's equation:
E=mc^2, or m = E / c^2
This last equation suggests that matter (m) is nothing more than extremely concentrated energy (E), or to think of it another way, a tiny amount of matter converts to an enormous amount of energy.
Light, or at least the visible light we see, is defined as a narrow band of wavelengths in the electromagnetic spectrum. Consider your usage of the term "Light" to mean all of the electomagnetic radiation that could be found in all of the electromagnetic spectrum. Energy can be measured in terms of electromagnetic wavelengths, so light, as we've defined it, means nothing more than energy, and enough concentrated energy is nothing more than matter, so
Electromagnetic wavelengths = Light
Light = Energy
Energy = Matter
Light = Energy = Matter