I like the ideas.

Needs a weaver to make the post look high quality but other than that all pretty funky.

I'm not sure the game operates with 'light' and 'dark' elements at the moment though, I think it's usually elements like wind, fire water etc., though I'm sure they could impliment them.

Dark Mage sounds much like a buffed up Thaumaturge, so if S.E decide that 1 class -> multiple jobs instead of the current 1 class -> 1 job they're doing now, a dark mage could very well be introduced in some way or another.

Light Mage, I wouldn't take an ability that's specified by time of day/weather conditions as it's too random and sometimes daytime just seems to fly by.

They both look like support types though, Dark Mage is a debuffer for enemies and Light Mage is a buffer for allies. FFXIV doesn't really have any 'proper' support types yet so they'd certainly have their niche somewhere.