Did some more research, tried a bunch of ideas, could not get beyond that intractable 'surface brightness' limit.

Went to 'Plan_B', more area. So, hauled model's OBJ into TurboCAD, trimmed it to just the four skinny 'LED Strips'. Carefully overlaid them with fatter hexagonal prisms. After saving WIP steps, deleted 'LED Strips' and saved the prisms as OBJ. Importing as % of figure was not going to work, so variously scaled as % of original. Hid lamp glass --Is double-layered-- and iterated hex prisms into place. Parented prisms to lamp. Un-hid lamp-glass to 95% transparency. Half-remembering comment elsewhere, and checking in manual, I set prisms to "Cast Shadows" OFF.

As 'Emission' goes no brighter than simply dialling 'Super Ambient', I reverted to 'SA' for both lamp LED strips and their hexagonal prism overlays. Latter have about 3~~4 times 'strips' area, so lamp is now about 'n+1' times brighter. Not brilliant, but much, much better. After a 64 pix-sample test-render (attached), I've sent a ¼ k pixel-sample to 'Box', just gone 50%...

I suppose next step is to overlay multiple concentric hex-prisms on each of these, doubling and re-doubling effective emission surface area ? I should be able to test that with Poser primitives... ;-)

I'll also have a look for Poser lights in run-time, hope to find some clue to how they by-pass 'surface brightness' limit...