Sun Strike is an Expert level Restoration spell that does sun fire damage to undead. 

I was a little frustrated that there was no restoration spell for dealing damage to undead higher than Vampires Bane, which becomes fairly useless at higher levels.

Sun Strike follows on from the "Sun Fire" and "Vampire's Bane" spells, and has a cost and power rating similar to that of "Incinerate" from the Destruction school.

The Spell Tome has been added to the leveled lists, and can be bought from Colette in the College of Winterhold once the player's restoration skill has reached a high enough level.

Needless to say, this requires the DAWNGUARD DLC to work.

Enjoy