The picture on my ultravision 50vg825 starts out bright, but after the tv has been on for a couple of minutes it dims. I have messed with the setting in the video menu and that doesn't help. And, yes, I have checked to make sure it isn't set to the preset night time setting :)

Televison & Video - Hitachi - UltraVision CineForm 55VG825 55" HDTV