I think they call it so because it's light coming from a projector, casting images like on a planetarium or domed IMAX theater. I noticed on the last few flashback sequences of The False Sun:
How? How could mere knowledge command such horror?
He will see for himself.
He walks into the golden gloom, squinting, staring. Dust puffs about his feet, particles blooming in the intrusive brilliance of the sun, then vanishing into the flanking darkness. He peers… notices a different luminance wavering across the interior, more fluid and sultry, webbed as though refracted through waters…
He hears it, a faraway wind, the groan of impossible multitudes–the collective shriek. His lungs become as stone. Horror makes pins of his skin. And he feels it, the burning vaults above, the smoldering glimpses...
Shaeönanra raises his eyes.
Edit: interesting to note, Shaeönanra's flashbacks are in the present tense, similar to Mimara's passages in TAE.
Imagine a parent explaining to a child that what they just saw was only a movie. Now transfer that to someone who has no concept of such things existing or, better yet, a sorcerer, who goes through their life cognizant of their scriptural damnation and now sees no mark on what they are now witnessing.
I like the line that Titirga suggests what the Mangeacca have seen is their goad, not their damnation, because it threatens to turn everything we think we know about the series on its head.
Is damnation merely the prodding stick the Inchoroi use to get sorcerers on their side? They created the Tusk and chose which traditions to collect, meaning they chose to include the scriptural damnation of sorcerers, despite there being Shamans in that age. Sorcery was what caused them to lose their wars with the Nonmen, it makes sense to nullify that advantage by bringing them to their side.
Also consider the Nonmen. I can't recall any mention of them fighting to forestall their damnation, despite being just as damned as sorcerers. It reinforces that this is just what the Inchoroi are telling men to get them on their side.
I think I was asked once, then what could the Inchoroi be doing all this for? And I look to Crash Space - they're bored. For a being whose likely lived thousands of years with no scruples
before landing on Earwa, battling sorcerers and chariots in the sky is the only thing that could bring excitement at that point. I know the dragon at the end of WLW suggested it's true - they're reducing populations to 144,000 to avoid damnation but we also know he is fucking with Achamian.
I think it would go well with the themes certainty and damnation if all this were the case and would be interesting if the this whole time, the faithful of the Three Seas were working to seal the doom of mankind and the Fanim were right.