The LCD's themselves have extremely low power requirements. A very small electric field is required to excite the crystals into their liquid state. Most of the energy used by an LCD display system is due to the back lighting.

I mentioned earlier that LCD's slowly transition back to their crystalline state when the E field is removed. In scanned displays, with a large number of pixels, the percentage of the time that LCDs are excited is very small. Thus the crystals spend most of their time in intermediate states, being neither "On" or "Off". This behavior is indicative of passive displays. You might notice that these displays are not very sharp and are prone to ghosting. Another way to building LCD displays uses an active matrix. The individual cells are very similar to those described above. The main difference is that the electric field is retained by a capacitor so that the crystal remains in a constant state. Transistor switches are used to transfer charge into the capacitors during the scanning process. The capacitors can hold the charge for significantly longer than the refresh period yielding a crisp display with no shadows. Active displays, require a working capacitor and transistor for each LCD or pixel element, and thus, they are more expensive to produce.