Artifacts in Heaven once have level 1 crystal stored in an accessory made of Heaven's Metal, a leveling system that doesn't exist back then since it doesn't have other levels, it just means that that level allows the artifact to store God's Light using an Angel's Light Magic called Gather Illumination spell, it gathers normal light but since it is Light Magic, it can also gather God's Light, although it's restricted.
Using the Gather Illumination spell only gathers light in an orb form in the middle of its magic circle, the higher the proficiency in this spell, the more the Angel could gather in their artifact, and of course, the bigger the illumination crystal, the more God's Light it could store.