The half lifes for flat panel displays nowadays are in the ten thousands of hours or pretty much on 24/7 for 15-20 years before you would see a picture dim. Short answer - much, much longer than you will probably keep the tv or else before something else may break- i.e. power supply short etc..
HT- 55" Sony 850c 4K HDR TV, Panasonic PT-AE8000 LCD projector, Elite Vmax Electric 100' screen, Pioneer Elite SC-71 AVR, Paradigm Titan Monitor v5 fronts, Paradigm CC-190 v6 center, Paradigm Atom Monitors v5 surrounds(x4), HSU research VTF-2 sub, Bowers + Wilkins ASW610 sub, HTPC/Gaming rig, Samsung 4K BDP, DirectTV HD-DVR, Roku 2, PS4,
Bedroom: RCA 40" 1080p, BD-player
Den - SEIKI 42" 4K LCD + RCA BDP
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