well I was thinking of using Bloom instead of HDR to get a couple more FPS and avoid nuclear dawns/excessive indoor lighting. however, I seem to remember that some widely used mods required HDR in order to function properly. I *think* it was AN but I really can't recall anymore. or maybe it was some OBSEv2 shader ( godrays I guess? ), umh... anyone happens to know? thanx guys!

The only mod I've had issues with is RAEVWD. From the readme:

I personally prefer bloom, especially with a bright LCD monitor, but as Arkngt said above, it doesn't work and play well with RAEVWD. I ended up installing a shader (RPG-BlackDragon Ultra HDR) to downplay the brightness, just so I could play without sunglasses. For the best frame rate, you can make a compromise by using bloom with Light VWD (http://www.tesnexus.com/downloads/file.php?id=15046), if you're willing to accept having only some of the distant structures visible--this is a combination I used successfully for quite a while.

thanx guys, that's the one! do you also have any idea if Bloom also has issues with vanilla LOD or with the Core package of RAEVWD that contains only optimized vanilla stuff?

Bloom lighting will have issues with LOD, regardless of who makes it. It's a flaw in the game engine that cannot be resolved by doing things to the LOD meshes, or by using less of them. Although using less of them means there's less stuff out there to trigger it, but that won't FIX it.

good to know, thanx Arthmoor

My simple solution is to play without either Bloom or HDR, I can load up on the visual bling including RAEVWD, high res LODs, QTP3 redimized etc and still have decent framerates. This way I miss out on black LOD objects (Bloom) and Nuclear dawn interiors (HDR). Tamriel still looks fantastic.