[Dylan16807]

>Again, that would require perfect reflection for that 85% of spectrum and perfect transparency and/or a perfect radiator for the other 15%.

What? No! You use a semi-good reflector that reflects 85%. You use any marginally-okay radiator and it will get rid of the other 15% No need for perfect materials at all.

>and the x% is capable of feeding all of the photosynthetic organisms on Earth it would be totally fine.

What? The point is to blot out 2% of the sun. You don't need the remnant light from that area of the sky to feed anything. Plants will just have to get by on having 98% as much light.

>Any imperfections will absorb heat and steadily destroy the shielding material in runaway overheating.

What? Any imperfections will make that part heat up slightly more, which makes that part radiate more, and then it reaches equilibrium. It's a sheet of plastic/metal. It's not going to be within a hair-thin safety margin of self-destruction.