Orlanth Lightbringer is the mystical and heroquesting aspect of Orlanth. He is a universally acknowledged aspect of Orlanth, worshiped in conjunction with the other Lightbringers. Orlanth Lightbringer is not a subcult – he’s worshiped as part of the Orlanth cult.
Even if I worship Orlanth Adventurous, Orlanth Rex, or Orlanth Thunderous, I worship Orlanth Lightbringer. He’s always part of the mix. He doesn’t provide me with special magic or have special Rune Masters. But there are places that are specially holy to him, like the Hill of Orlanth Victorious.
What other deities share this identity aspect or is this particular to Orlanth? Orlanth is the leader of the Lightbringers but Chalana Arroy, Eurmal, Issaries, and Lhankor Mhy are also all Lightbringers. Orlanth Lightbringer unifies them all.
So if you are wondering if there should be some special list of spells or other mechanical benefits for Orlanth Lightbringer, the answer is simple – nope. But the aspect actively supports the idea of heroquesting, which is pretty uncommon in other cults.