Does anybody actually use this skill, or could it use revamping? While it's cheaper, the damage output isn't nearly as nice as blazing, which is why blazing is always the go-to morph. Because this skill scales from max health, if you're running Sun Shield, you probably have a lot of HP and small magicka reserves, which means you invest a lot in cost reduction. That said, this is why the cheaper one didn't even appeal to me. With channelled focus costing 280 magicka, I can pretty much keep blazing shield up all day long, even with a 15k magicka pool.
I would suggest removing the cost decrease of Radiant, then amping its damage and range slightly.
If anyone is actually using Radiant, I'd really love to hear how you're getting on