A pillar of intense, bright light will appear from the heavens and strike down onto the target area. Adaptations include one short burst against a single strong enemy or a devastating area attack against groups of enemies.
Damage of Radiant Pillar is affected by Intelligence, so you need to invest in this attribute to make it effective.
Bronze choices: Hypnosis may be considered useful if followed by Flaring Nova, Archangel's Wrath (explosion mod), BeeEffGee (pierce mod). Otherwise Delude is a very good option especially when combined with Baneful Smite with another attack value reduction mod.
Silver choices: Duration will come naturally with leveling. It will eventually be longer than you ever need. Therefore taking Brightness seems like a better choice than Conserve.
Gold choices: Ordeal effect can be easily obtained with items (in Fallen Angel only, this was changed in the Ice & Blood expansion). Straight damage from Magnify is a very good choice.
The Delude mod uses a particular formula to calculate the attack value reduction: 1-1/(1+(650+10*CA lvl)/1000). For level 1, this gives 1-1/(1+(650+10*1)/1000 = 39.8% reduction, level 10 gives 1-1/(1+(650+10*10)/1000 = 42.9% reduction, level 50 gives 1-1/(1+(650+10*50)/1000 = 53.5% reduction.