It is known that  the working principle of crt is that the filament is heated after being  energized, the cathode is excited, and the electron current is emitted.  The electron current is accelerated by the inner metal layer with a  high voltage, and the lens is focused to form a very fine electron beam  and hit on the fluorescent screen. Make the phosphor glow. And  crt principle is completely different, lcd needs from the back of the  light source, when the light beam through the layer of liquid crystal,  liquid crystal will be side by side or an irregular twist shape, so the  LCD is more like a gate, select the light penetration or not, we can See different shades of picture on the screen.
At  present, the mainstream liquid crystal display is a thin film  transistor lcd (tftlcd), which is an extension of the original liquid  crystal display technology. Tft liquid crystal has  a semiconductor switch for each pixel, so as to completely control a  single pixel, the liquid crystal material is sandwiched between the tft  glass layer and the color filter layer, and the voltage value of the  liquid crystal can be changed by changing the voltage value of the  liquid crystal. Controls the last light intensity and color that appears.