Surely your species' understanding of physics has at least covered matter to energy conversion? Same principle, except in this case the energy is stored instead of being released. Light's just the medium of energy.

[He takes the pillow from where his head was resting, shakes it out a little, and passes it into the Armiger with a flurry of blue lights to demonstrate.]

It gets a little more complicated when you get into the matter of the Royal Arms and other such things, but that part's straightforward enough.