HDR rendering dynamic range

I’m trying to render out a scene as HDR so that I can add some post effects for glare and the like. In this case with iRay and to adjust in ArionFX for After Effects, but this is kinda general I think. I’m having a heck of a time tying to get the effects right where I want them, it’s a ridiculously delicate balancing act to get just precisely the right glare effect, it’s either nothing or totally blows out the image(I got it right once then I had to change the lighting,) like it seems that something might be wrong with my rendering. How can I tell using Photoshop or something just how much dynamic range is actually in my render?