The only difference between the two is how the light is generated at the back of the screen.                                        

How an LCD Television Works

LCD television screens are made up of liquid-crystal gel sandwiched between two panes of polarized glass. When you power on the television, the electric current passes through the liquid-crystal display, altering its structure. The liquid-crystal molecules coil and uncoil. This creates a shuttering effect, whereby light is either allowed to pass through or not. This variation in light and dark on the screen, is what the viewer perceives as images.

Unlike plasma TVs, the liquid-crystal does not create its own light. It requires another light source. In the case of LCD TVs, the screen is lit by fluorescent tubes.

How an LED Television Works

An LED TV is just a new generation of LCD TV. The difference, is that an LED TV is not lit using fluorescent tubes, but rather a series of light emitting diodes (LEDs). There are three basic types of LED televisions, and each has its own specific format.