The first LCD panel technology in mass production is called TN (Twisted Nematic). The principle behind the LCDs is that when an electrical field is not applied to the liquid crystal molecules, the molecules twist 90 degrees in the LCD cell. When the light either from ambient light or from the backlight passes through the first polarizer, the light is polarized and twisted with the liquid crystal molecular layer. When it reaches the second polarizer, it is blocked. The viewer sees the display is black.
When an electric field is applied to the liquid crystal molecules, they are untwisted. When the polarized light reaches the layer of liquid crystal molecules, the light passes straight through without being twisted. When it reaches the second polarizer, it will also pass through, the viewer sees the display is bright.
Because LCD technology uses electric fields instead of electric current (electron passes through), it has low power consumption.