Standard military paraflares that I've looked up illuminate a radius of about 55 m, corresponding roughly to blast power D.
Not sure what altitude they reach, but the real question imo is how far away you can reliably put the illumination.
55m is not blast power D. Blast power D only has a single-hex effect. Blast power A or B is more like it.
In any case I have a decent amount of experience with some old surplus east bloc flares. Especially ones we called "Czech comedy flares" that are a handheld tube-fired thing, similar to the Russian ones. Dunno if it was just age or they were always like this but the effectiveness varies wildly
. Sometimes they work as expected, lighting up a pretty good size area (50-100 meters seems right) with colored light (red, IIRC - probably there were some options) for nearly a minute. Other times they would immediately shoot off in an extremely not-straight direction out of the tube at high speed, smacking into a tree or whatever 10 meters away and being useless/a liability. Sometimes they would snag in tree branches on the way down, which was a benefit as it meant they'd function for slightly longer, the taller the tree was!
But yeah, low-tech illum options like these will be important. I agree that they might create an area of good vision but still count as dim light for purposes of shooting at anything within.