Helios drives the chariot of the sun across the sky and sees everything that happens beneath it, which is why oaths are sworn before him. He is the witness of the day rather than its ruler: in Greek telling the sun is his work, not his throne.
Modern Practice
Call on Helios for clarity, for the exposure of what is hidden, and before making a promise you intend to keep. He is a daylight deity: work with him at dawn or noon, and treat the honesty he brings as the point of the practice.