The Casio high speed camera has arrived! An exclusive from The BlurBusters Lab: A high speed 480 fps video of an LCD refresh. This video shows the pixel refresh in super slow motion. (silent video)
This is a 2007-era LCD monitor, not suitable for a scanning backlight, but illustrates the pattern of an LCD refresh, and helps explains why a scanning backlight needs to be synchronized to the pattern of an LCD refresh.
3D-compatible 120 Hz monitors use a different refresh pattern than this. They refresh individual frames quickly (nearly instantly) due to the requirement for static frames for shutter glasses. Thus, these are compatible with a simpler full-backlight strobe, eliminating the requirement for a sequential scanning backlight.