The Cave Illuminator is great! How about a Starlight Illuminator for the surface?
It would only need to provide enough light to get rid of the red/yellow X's from F7.
I would expect that the range could be boosted with a linked collector crystal.
I think that's the same level as a Redstone Torch, but that is conjecture.

Further, you could provide further upgraded illuminators at higher levels...
say Lunar Illuminator and Solar Illuminator later, with more light levels/range later.

Seems overly unnecessary. If you want to light up large areas, there are other, existing solutions. On top of that, it would just add more clutter and being non-trivial.