It may seem obvious to some, but unlike my own laptop where I turn the backlight down to save power, I never really considered it to do the same with my led-backlit tv!
You can verify it easily enough even with a consumer level meter like a P3 International Kill-A-Watt meter.
In my case, I was testing a backup satellite tv monitoring system, which was a simple system of nothing more than a large Optima Blue Top, a pure-sine-wave inverter to power the system.
When I turned the system on, I was running at about the max amount of led-backlighting pulling more than 100 watts. With the backlight just above zero, only 45 watts.
Certainly it is not ideal to watch in a very bright room, and I use the system for emergencies, but what was really apparent was the real power reduction even from a moderate decrease in backlighting without destroying viewing pleasure.
I actually got used to it, and after a few small adjustments for brightness to somewhat compensate, it is saving a lot of power for my non-battery usage now too.
So armed with a meter like the kill-a-watt, you can easily see what you can live with and how much power you can save.