Prismatic Light doesn't seem to do anything for either my Cleric or my Sorcerer.
Granted, my Light skill is low right now (Sorcerer is Expert with 5 points, Cleric just has 1 point) but all that seems to happen is a weird sound plays while the caster grimaces.

On a note that may or may not be unrelated, any tips for dealing with Eyes? They're taking forever to kill (party is past Level 50 right now and can do between 25 to 50 physical damage) and there's always a horde of them.

Could it be you're trying to cast the spell outdoors? It only works indoors, as far as I remember.

As for the eyes, they're absolutely the worst enemy you can encounter. They're not really dangerous as they don't deal much damage, but their effects they cause are so annoying and add to that the fact that they take ages to kill. I found Dragon Breath worked best on those bastards.

I know I tried Prismatic Light indoors because it was actually Agar's Laboratory where I last tried it.

I'll see if Dragon Breath will do anything. I haven't picked up Dark magic but now I'm considering it.

In MM6, Prismatic Light deals "Magic" elemental damage, which many lategame enemies are immune to. Most of the Self spells work the same way, but you should be able to get results out of spells like Inferno (fire), Toxic Cloud (poison), or Blades (physical).

I loathe Eyes. My only real advice against them is to hire a Cartographer; they keep up the Wizard Eye spell constantly, so the Eyes cannot dispel it.