It always bothered me that ADAM mod authors never ended up addressing this bug, so I ended up fiddling around trying to fix the issue myself. As a complete idiot and beginner when it comes to modding, I basically started with a fresh download of Nifskope, one possible lead, and a dream. According to what others before me have attempted, the closest they've gotten to solving this conundrum was deleting the alpha property (NiAlphaProperty) in nifskope on the riot gear helmets. This resulted in the lighting bug apparently being fixed, but introducing a brand new problem in the form of an texture-less black hole of a blocky additional mesh slapped onto the side of the helmet that also didn't look quite right, and that just wasn't good enough for my OCD. I tried everything I could come up with from trying to delete that part of the mesh and the triangles associated with it, to re-sorting the now out of numerical order nodes in a vain belief it might solve something.

Frustrated and bitter over genociding my sanity, I had a eureka moment. I copied the NiAlphaProperty flags/settings from parts of the riot armors that worked and did not exhibit the lighting bug over to the helmets and VOILA. As far as I can tell, the helmets don't freak out in indoor lightning anymore and nothing appears to have broken.

Although I intended this tweak to be for personal use, I decided to put it up on the Nexus hoping it might also fix it for you guys, and spare you the roundabout on the 5 stages of grief.

Installation: Drag and drop to replace the meshes from the original ADAM/ADAM Reborn mod. It's a mesh replacement, come on now...