I read about how an LCD screen works here, and it made me wonder what actually happens when the screen shuts off. Based off of this, I can think of several possibilities:
Electricity is supplied to all the pixels/crystals, thus making them all appear dark. While this fits with the on/off explanations given in that article, it seems like a significant waste of energy to use extra energy when not in use.
Electricity is not supplied to all the pixels, which would light them all up, but the backlight shuts off, so the screen appears dark.
Electricity is maintained to the pixels that were receiving electricity when the screen was on, but the backlight shuts off so the screen appears dark.
I would be curious to know if different phases of the off screen are different (such as a off-screen-like screen saver versus a sleep mode or being shut off, etc.).