Lightsabers are powered from the control studs by a circuits channel and focusing crystal found only in nature on the planet Ilum. Before 1,000 BBY, the Jedi also used crystals from the planet Ruusan. This appears to be a matter of tradition rather than necessity, as there are many examples of crystals from elsewhere in the galaxy being used effectively in lightsabers, particularly with the revival of Jedi Order after the downfall of the Empire. Since the Jedi control the supply of suitable crystals, the Sith use synthetic crystals that generate a red blade. Some of the early Sith had other blade colors, but as fallen Jedi they might have re-used the crystals of their old lightsabers. Shadows of the Empire has Luke Skywalker using a synthetic crystal in his lightsaber construction. Luke built a lightsaber with a green blade, implying that the Sith intentionally construct their crystals to produce a red blade. Green blades can also be created from Corusca Gems from the gaseous planet of Yavin (Jacen Solo used a Corusca gem for his lightsaber) or any green-hued crystal capable of withstanding the strains of having so much power flow through them. This is true of other hues, as well. Natural crystals are usually prefered to synthetic, as there have been instances of synthetic crystals failing at unfortunate times, as happened to Corran Horn in I, Jedi.