What do you think the difference between a mage of light and a mage of void ?

The Aspect? Some are more abstract like Blood and Breath, but Light and Void of all things is one of the most starkly complementary pairs there is. Information and Truth vs Lies and Obscurity, Relevance vs Irrelevance, Skaia vs Horrorterrors, Light vs Darkness. Curiously enough this likely means anything a Mage of Light couldn’t be able to Know may just fall under the Mage of Void’s realm of Knowledge.