excessive brightness

[andysvolvo]

samsung sp42w5hfx this tv may stay normal brightness for an hour or so then start to get extremely bright till i switch it off.
all guns may drive too hard sometimes then onanother occasion it maybe the green gun or on another the blue etc, there is a small amount of smearing on the colour when viewing white writing and stationary pictures.
all other functions working correctly.
any help please very very grateful
andysvolvo