I'm getting the same thing the past few days. 9900 on OS 7.1.0.391.
Screen dims after just a few seconds....annoying. So I go into back light settings, re-save my 20 seconds backlight timeout and it seems to be fixed...for awhile! Eventually it starts dimming after a few seconds again.
Battery saving mode is on but only set to come on below 20% battery. This dimming happens when battery is well above that.
Here are the apps I have running that are the same as the OP:
BB Protect
BeBuzz
BeReader
BeWeather
Pattern Lock
I have a feeling it might be Pattern Lock messing things up since I just installed yesterday and I think just noticed this dimming happening around the same time. Uninstalling pattern lock to see if that fixes it.
UPDATE: DELETING PATTERN LOCK SEEMS TO HAVE FIXED THE PROBLEM!
Looks like (Secret battery saving mode has been activated)
Sorry but i have no idea whats causing that, Battery saving mode does the trouble sometimes tho