Let's say a character has the exalted feat Nimbus of Light (this is just an example) which makes him shed light:
Your radiance sheds light as a common lamp: bright light to a radius of 5 feet and shadowy illumination to 10 feet. You can extinguish this radiance at will and reactivate it again as a free action.
What would happen if he enters the area of a Darkness spell?
Normal lights (torches, candles, lanterns, and so forth) are incapable of brightening the area, as are light spells of lower level. Higher level light spells are not affected by darkness.
Since the light is supernatural (all exalted feats are supernatural) it doesn't qualify as "normal", it could qualify as a spell, but supernatural abilities don't have "levels", and often, as in this case, they don't emulate the effect of a spell like most spell-like abilities do.
So, what would be the proper way to resolve this kind of situations, where magical darkness interacts with supernatural light, and magical light interacts with supernatural darkness?