Originally Posted by
GideonHighmourn
That's incorrect. The skill only effects Cast Times, lowering them by 20%. It doesn't increase the "Spell Speed" stat on the attributes window anymore. Similar to the new Selene buff, it acts as a "haste" effect, but doesn't effect the actual spell speed stat.
Also, Light Speed is great for a spell like Stoneskin or Ascend, however, using it on heals is fighting an uphill battle. While it lowers the cast time, it doesn't effect the GCD (AFAIK), coupled with the -25% potency decrease, you're fighting an uphill battle trying to keep up with damage.