my tv is a 52 inch, and periodically the screen goes darker

[lexismom]

My tv is a 52 inch and periodically will go a little darker.

 

[clutchc]

Best call a technician. Might be the back light dimming due to failing, or its transformer. It might be the processor chip controlling brightness. Can't be sure w/o troubleshooting.

 

[R_1]

A long shot but, does the TV have an auto brightness setting?
if the brightness is set to auto the brightness will dim when the ambient light dims.

 

[clutchc]

+1^
Good point.

 

[jsmithepa]

Turn all Green Modes OFF.

 

[R_1]

I think I have it. I was reading an article on Ars about TV power consumption and ran into this little jewel, and it would seem to be the answer to your issue. I hope anyway. from the article on Arstechnica.com

"Samsung, LG, and Vizio TVs use a number of tactics. Motion-Detection Dimming (MDD) software (called “Motion Lighting” under Samsung and “Motion Eye Care” under LG) will dim the TV’s screen when a certain amount of motion is detected in the image the viewer is watching."

You may want to search the menu for something like this and turn it off.