The problem with the "lighting" in the new buildings at the NMUSAF is first, and foremost, that the bloody walls/ceiling are painted BLACK.
If I remember correctly, the Museum Director commented favorably during the design phase that he thought the black paint would be "dramatic" and approved the design, which also uses several hundred theatrical type spotlights. Well, it might be "dramatic", but it sure is d-a-r-k!
I defy most people to find the U2 hanging over the B36 in the new building. Let's see...a very dark aircraft hung up near a very dark ceiling..dramatic, eh?
The other brighter gallery you speak of is not really any brighter, or not much brighter, than the new buildings. But, it is painted white and everything is more visible as a result.
Photo tip - if you still use 35mm film, use only 800 ASA (or better yet 1000 ASA) film anywhere in the museum, or have a real good flash. Those who use most digital cameras can usually only increase the simulated ASA on their digital camera to about 400 ASA...not really fast enough for all but close-up photos in the NMUSAF.
Don't get me wrong, I really like to visit the NMUSAF and have been a member of their "Friends" for about 2 decades...but, I try to look at the aircraft and try not to think about the lighting and visibility problems when I visit. One of my all-time favorite photo's is of the nose of Sacred Cow (in the annex) with the windows in the hangar doors reflected in the polished aluminum. It's nice what you can do with available light...when there is some.