A power system having a DC electric motor is disclosed. An insert, or shoe, is placed at the bottom of the heat cup containing the fluid to be tested. From these stacked cell assemblies visible light is emitted of a desired color or color temperature and brightness. The system may also incorporate an optical element wherein the reflective surface includes a continuous array of convex elements extending outwardly from and across one end of the optical element and wherein each of the convex elements defines a critical angle.