AVS Special Member
Join Date: May 2008
Location: San Francisco - East Bay area
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Lower backlight settings produce darker blacks. In a perfect world, you'd set the backlight at it's lowest possible setting and get the light level you need (30-35 fL in a dark room is fine) with Contrast.
In the real world, the Contrast control may blow-out highlight detail if set too high so you have to check bright steps with a test pattern that will show if you are crushing highlight steps (say digital 220-254). A lot of people think it's blasphemy to crush steps in the range of 236-254, but, honestly, there's no image detail at those levels, you only get "specular highlights" up there... reflections from chrome, water, crystal chandeliers, etc. I doubt there are many people who can "see" any difference in images where steps above 235 are crushed. But you DO NOT want to crush any steps below 235, ever.
The other real-world issue is that on some TVs when you use very low backlight settings, the color balance can get very odd because the backlight (LED or fluorescent) has a significant color shift at low output levels, so you have to watch out for that also. I often calibrate 100% white with the backlight set in the middle of it's range, then decrease the backlight to it's lowest setting and remeasure 100% to see how much of a shift there is. If the shift is minor and can be corrected with the TV's CMS controls, the lowest setting could be usable if Contrast goes high enough to get you to 30-35 fL. It's a balancing act. You may find you have to increase the backlight setting 1 or 2 or more steps to get Contrast into a usable range. There's a lot of variation from brand to brand and model to model.
"Movies is magic..." Van Dyke Parks
THX Certified Professional Video Calibration
Widescreen Review -- Home Theater & Sound