Hi Friendly! I have seen people and minions cast Guiding Light. Do you know where you learn this spell? It is very helpful for life people.I love Guiding Light! It *IS* a great spell. In fact I use it all the time on Amber Deathsong when I'm playing her character or when I'm playing my own Life wizard, Molly Earthsong. For anyone not familiar with this spell, it's a blade-like buff that floats around your character's head and give +30% healing.
Unfortunately this isn't a spell you can put in your spellbook unless you're a Life Wizard. At the end of Marleybone you complete a quest called, "Bad News...." After completing this quest, all wizards (except ice wizards) get a new spell! This spell for Life Wizards happens to be Guiding Light.
Fortunately though, there is a necklace with this spell on it!
You can buy this necklace at the bazaar, in Marleybone's necklace shop, or if you'd like you can farm up your own from The Great Troll on Colossus Boulevard.
Notice that the spell from the necklace is +40% healing, so can stack this Guiding Light with the regular Guiding Light spell and then you're a crazy awesome healing machine!
You mentioned that minions cast this spell. You are correct, the life minion does cast this spell quite often, and we love her for it (it's just those darn imps she casts that we don't like . . . grumble).
Thanks for the question!