Light is the eternal force that, along with darkness, makes up the KH universe. It's commonly associated with good because of it's supposed nonviolent nature, though this is not true. Sora's Keyblade represents Light. This is not to be confused with Roxas' element, which is simply a basis of his powers and isn't actually categorized as any specific element. Mickey's keyblade also represents light but in a somewhat different form that that of Sora's, seeing as how the four keyblade masters are representative of different aspects of light and dark, his represents the dusk, while Sora's represents day. This in turn is different than that of Riku's and Xehanort's keyblades which represent darkness.