Hi I was wondering if anyone knows what causes this type of glitch? And whether anyone else has noticed this type of glitch (Regardless of location)?

http://www.youtube.com/watch?v=hlSV340M2EU

I've noticed that the occurrence of this type of glitch can be a bit random at times, and It's been driving me insane trying to get to the bottom of it. Basically the smoke isn't being lit by the light all the time, popping in and out. While at the same time the light is visibly still on.

P.S.
Just some background information regarding the video. Though I've seen this glitch occur on an un-modded Skyrim, the video I've linked shows my modded placement of a light in Whiterun. I initially thought that maybe the glitch had something to do with the light placement, so I tried the following. I reset the three light sources I edited in that vicinity, back to their defaults, so as to start fresh. Once I had done that I tested in game and the glitch was gone. I then edited those light sources, tested again and the glitch was back. So I once again reset them, however this time the glitch was still present (Which illustrates the somewhat randomness of it). The other thing of note is that there aren't any over lapping light sources, which can sometimes cause glitches, which is why I'm so stumped.