for some reason I didn't check the date on the original post. i'm sure you're far beyond 12th level by now. Maybe the info will help someone else out tho.
No it won't. The + Element values on armor only affect your defense against said Elements, so in this case you will resist Light-based damage more effectively. I'm not sure if affects resist rate or lessens damage outright but it definitely does not affect your own Light-based spells (99% sure of this). Hope this helps. As a mage I would suggest Energy Earrings at this level.