I read a thread where someone's neck board was loose and securing it brought the brightness back to standard. I have a presentation monitor where the brightness seems off, so I took the back off to see and found the following things interesting. The first two photos show the back interface panel is actually an additional feature. The last photo shows what I realised is the sub of the built-in speaker system.
(Alas, the neckboard seemed secure, so now change there. As well, my candy's monitor has what seems a similar situation and the neck board wasn't on all the way. Again, however, when pushing it all the way up there was no change. Ah well.)