2011 iMac Brightness Flicker

about week ago started noticing screen brightness randomly changing on mid-2011 27" i7 imac. screen darkening equivalent of 1 2 brightness settings full brightness, typically have set during day. flickers second or two, stays @ darker setting several minutes.

do not have ambient brightness change setting checked in display control panel. i'm running snow leopard 10.6.8 , have performed pram , smc reset.

i'd find out if potentially system/firmware issue, or if points physical problem backlight, power supply or video card. know led screens adjust brightness modulator, not sure if located in power supply or screen itself. imac still under warranty, i'm loathe have haul in apple store, particularly since intermittent problem.

has else had issue?

 

after spending more time imac, realized yesterday brightness changes occurring on left side of screen. after searching "half screen dark," found these threads:

https://discussions.apple.com/thread/3280437?start=0&tstart=0

https://discussions.apple.com/thread/3081411?start=0&tstart=0

appears lg panel used in 27" imac utilizes 2 led backlight bars, located on left , right sides @ bottom. whatever reason, left light bar seems more prone failure , apparently going bad on imac.

have contacted apple service, though able fix or replace backlight without replacing entire display panel module. current screen until has been perfect no color temperature differences (yellowing) or other issues, , extremely disappointing inferior replacement.

way, photo below (from thread above) shows experiencing.

 

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