CFL TV does not change backlight intensity dynamically, you can adjust it to desired level, but once done it stays that way regardless if the scene is dark or bright. You need LED backlight for dynamic changes in light level depending on the scene. What changes during video display is the amount of twisting of LCD crystals, depending on the voltage applied, more voltage, more twisting towards 90 degrees, more backlight passes by towards the viewer, brighter the picture (actually you can have design where crystals are aligned to block all light with 0 voltage and open up with voltage, or be open with 0 volts and twist to close light with voltage applied.) The amount of that crystal twisting needed to display picture properly is calculated by video processors. Lets say digital video signal comes in and calls for medium gray:128,128,128. So now video processor looks at your calibrated settings and adds offsets to each subpixel to keep it gray (lets say your colors were too red so you added some corrections) so now the numbers are 100,135,115 and it's translated into proper voltages, send to crystals to twist proper amounts, so you see gray. The same way processor adjust for contrast, color and brightness by adding proper offsets to each subpixel. To keep it as simple as possible I'm not going to go into color dithering and other aspects of additional video processing.