Perhaps the Luminaries are summoned by priests and obey them, while Light Elementals appear on their own and are uncontrollable.
Description of Light Elementals:
Light Elementals usually appear at dawn, when a pale pink light reflects off the clouds and dew, taking on a visible form. These spirits are often friendly and willing to help lost travelers. Although they are related to the Luminaries summoned by the followers of Elrath, the Dragon of Light, Light Elementals are more wild and do not obey anyone, preferring to judge the purity of the soul of those they encounter according to their own standards. If angered, they emit flashes of blinding light. The priests of the Empire, due to their devotion to Elrath, have a natural affinity with Light Elementals. Among them, there is a matriarchal order called the "Weavers of Light," which is dedicated to finding newly born Light Elementals and weaving them into sacred fabrics, from which the robes of the Empire's heroes are created, or into colored glass, from which magnificent stained glass windows are made for temples dedicated to Elrath.