While in the Soul Cairn, when I got near a large soul gem I experienced the soul drain effect. Typically when I move far enough away from the large soul gem, the drain effect stops. Well, the drain effect didn't stop this time and continued to follow me through the entire Soul Cairn. I was thinking the effect would stop when I exited the Soul Cairn, but it is still happening in Skyrim. I have tried fast traveling to a new location and reloading a save, but the drain effect is still happening to my character. My health is not being depleted, but the drain effect is so annoying and is interfering with my view. The effect stops when I transform to VL. When I revert form back to my character, the effect appears again. Are there any known fixes or has anyone else experienced this?

Have you tried eating a soul husk, or drinking a soul husk extract potion?

I am stuck with this particular annoyance. I have confirmed that the light is purely graphical, that is, unlike one fear I had, it does not appear to be a visible light to others like a torch which can give you away sneaking. In spite of that, and even if there is no actual drain effect, it is much more than an annoyance. An ice spike in the head (which I believe is the same type of glitch) I could live with. I use first person all the time anyway, but this light does interfere with playing. It can and does flicker about you, flashing your visibility completely out in spurts as though you were in a bright lit area with nightvision on.

I'd like to believe it can be undone by doing the quests there in the Soul Cairn (the rest, I did Beyond Death). I cannot even attempt the supposed workaround for the Breezehome alchemy lab bug of removing the DLC and loading a save. That was suggested somewhere, but it will not load a save that depends on missing content, so it's garbage. I didn't notice the effect until the set of five saves I cycle through were already all overwritten with saves after I had the bug.

I tried searching too the other day when I noticed it, but only found one or two places where people mentioned it happening to them. It wasn't even listed in that maintained bug list thread I found here. I realize Dawnguard is still too new for every quirk to have been found much less fixed, but for the love of god, can anyone tell us of a way to get rid of that damn light?!

I did both those and it had no effect. I did notice it vanish when I changed to a vampire lord like he noted. For all of a few seconds I was thinking oh thank god, just gotta transform to lose it. Nope. Revert and there it is again. My test of whether it was an actual light that could give you away was basically to move into shadow and when the shadows didn't vanish or lessen around me, I concluded it was merely graphic leftover akin to that ice spike one.

Very interesting (note: I do not find this problem amusing). I'm no expert with these types of issues, but I'll give you a list of random ideas:
-read an elder scroll (maybe the flashy blindness will fix it)
-get killed (just a thought)
-walk back under the soul gem (you've probably already tried this)
-jump in one of those portals in the soul cairn (the ones that cloud your vision with black goo)
I can't think of anything else that would have a chance of helping right now...

I hadn't tried anything other than reloading or changing into a vampire lord and back. However, rejoice all ye frustrated souls! i just found a way to get rid of it.

I had to share it as the most frustrating part of this whole thing is not being able to find a damn thing about it online. Nothing. Google every relevant term you want, search through this forum's search feature, it matters not. Almost nothing to help you at all. Hell I barely could find any mentions of the bug itself (as I mentioned before, that compiled bug list thread does NOT mention this).

After reading about it and people seeing things change upon teleporting, I figured if there was a way to undo it, it would surely be found in the Soul Cairn. I went there in search of one of those big gems. I mentioned that I ate the soul husk food and drank one of the extract formulas. This was outiside Soul Cairn. First thing I tried on entering again, but no luck. So I went roughly due east until I came across a fort with one of the big gems in it. I figured what would happen if I got close to it again since I was certain the graphic was the drain effect. I did and sure enough it began doing it. I ate a husk and it stopped. AND THE GRAPHIC VANISHED TOO!!!!! I ran out before the minute of the effect could wear off just in case, but I'm back on the outside right as rain.

To recap for any afflicted by this sight obscuring bug: go back to the Soul Cairn, find and walk up close to one of those big floating soul gems until it begins a new drain animation, eat soul husk, then skidadle on out. Fixed.

Yay! The suffering ends.