LUMI. - Distinct insights, of a theoretical or practical order, destined to guide the soul in faith or in action.

They belong to the discursive order, taking on the aspect of clear and luminous syntheses, of truths that can be reached through adequate reasoning, but which in this case are perceived more rapidly and vividly. They might be called conclusions which, instead of being gathered with prolonged mental toil from a complex of premises, result from a few operations. They usually occur especially in persons of great intelligence, dedicated to meditative prayer, and accustomed to abstract essential truths from the contingent, but also in simpler souls, and then ordinarily more passively through infused gifts.
Lumina are often sudden, similarly to the so-called strokes of genius, and cause a deep penetration into the science of heavenly things (attributes of God, mysteries of the life, death and resurrection of Christ, providential events, relations between the Church, the Pontiff and the spiritual life, etc.). Being personal and not ordinarily retracing already elaborated subjects and schemes, they fix themselves more firmly in the soul that enjoys them, moving it more effectively toward goodness and holiness. They are more frequent in the period of ascesis known as the illuminative way.
Arnaldo M. Lanz