It may be the Eco Solution option (also found on page 18).
The light in the room may have adjusted, and this feature can be turned off. To do this, use your remote and press:
Menu > Picture > Mode > Eco Solution> Eco Sensor > Off
Does that help?
HI, just noticed last night on my new Samsung LED 55". The picture will get a get a little darker for a few seconds, then will revert to the normal brightness. At first, I thought it was the program doing this for effect, but then it happened a couple times while watching the news. Does this signal problems down the line. It's only about 3 months old...
Model number: UN55C6900VFXZA