When placed in a multiblock structure (as described below) with a clear view of the sky and a Glass Lens put into it, the Spectral Relay will bring more starlight to the closest Luminous Crafting Table (or any upgrade) in a 16 blocks radius around itself. Multiple Relays in a 16 block radius will have diminishing effects.
When placed around an Iridescent Altar on the sooty marble, Relays will be highlighted during crafting, showing an image of an item to place on them to continue crafting.
The complete structure is 3x2x3 and requires (in addition to the Relay):
The fosic resonator can find fields of intense starlight which can be useful for harnessing the energy. The problem is moving infrastructure or traveling vast distances to harness the starlight can at times be impractical. As delving further into the secrets of the Ancients will undoubtedly require more and more starlight an alternative is in order.
A small setup, dedicated to collecting starlight for the altar near should help solve that problem. A clear view of the sky is most certainly a necessity and better results will most likely be achieved at night.
When the relay has been placed high up but close to an altar, it will collect and focus starlight once a glass lens is placed inside it. The starlight is then redirected as small sparks to the closest nearby altar.
However, placing too many relays close to each other will result in one cannibalizing the others' starlight and will most likely create much more... disappointing results..