How LCD Works

A projector’s job is to taking the electric signal from a source, transform that signal into an image, and project or display it onto a screen. For this to happen, the signal must be converted into a digital signal. This digital signal is then sent to a display image. This image is a LCD (liquid crystal display). To understand how LCD projectors work you first know how LCD works. Here are some things to think about:

 

·        LCDs: LCDs are used because they provide much needed advantages including drawing less power, and they weigh less.

·        Liquid crystals: Liquid crystals are neither solid nor liquid. Why? Because the molecules in solid matter stay in one place while molecules in liquids matter wonder from place to place. Liquid crystals don’t do either way. However, as matter, they are more liquid than a solid. Liquid crystals are very sensitive to temperature, being that they can turn into a real liquid at the slightest rise in temperature.

·        Nematic Phase Liquid Crystals: There are many types of liquid crystal substances. The nematic phase is what makes LCDs work. One particular nematic liquid crystal used is the twisted nematic. Liquid crystals are affected by electric current. When an electric current is applied to this crystal, the crystal is untwisted. Depending on the voltage applied will depend on the amount of untwist involved. Because of this predictableness, they are used to control light.

·        External light source: Liquid crystals do not emit light. They only reflect it. This means there has to be an external light source. In order for LCDs to work, small electrodes charge the liquid crystals so as to make them untwist. This untwisting block light from transmitting through the polarized film that is part of the liquid crystal. In most displays, there are little fluorescent tubes built-in above, beside, or behind the LCD that work to light the display. In this case, a white diffusion panel used to redirect the light in an even way to make sure the display is covered.

·        Passive Matrix: This type of LCD uses a simple grid to send charges to a certain pixel for it to allow light to go through. There are rows and columns that of liquid crystals that are connected to an integrated circuit which controls the charge to these crystals. To activate the liquid crystal, a voltage is sent down one column, while a ground is activated in the row. When the row and column intersect, the voltage is applied and untwists the liquid crystal.

·        Active Matrix: Active-matrix LCDs work with thin film transistors (TFT). These are tiny switching transistors use capacitors to energize them. To turn on a particular transistor, a charge is sent down the right row. Another charge is sent down a column. Since all other rows and columns are turned off, only the one row and column are energized. The capacitor at this point receives the charge, which in turn sends the charge to the transistor.