How Does It Work?


LCD (Liquid Crystal Display) panels are "transmissive" displays, meaning they aren't their own light source but instead rely on a separate light source and then let that light pass through the display itself to your eye.

We can start to describe how an LCD panel works by starting with that light source. The light source is a very thin lamp called a "back light" that sits directly behind the LCD panel as shown in Figure 1.

LCD Panel Inside
Figure 1

The light from the backlighting then passes through a polarizing filter (a filter that aligns the light waves in a single direction). From there the now polarized light then passes through the actual LCD panel itself. The liquid crystal portion of the panel either allows the polarized light to pass through or blocks the light from passing through depending on how the liquid crystals are aligned at the time the light tries to pass through. See Figure 2.

How Liquid Crystal Works
Figure 2

The liquid crystal portion or the panel is spit up into tiny individual cells that are each controlled by a tiny transistor to supply current. Three cells side by side each represent one "pixel" (individual picture element) of the image. An 800 x 600 resolution LCD panel would have 480,000 pixels and each pixel would have three cells for a total of 1,440,000 individual cells.

Red, green and blue are the primary colors of light. All other colors are made up of a combination of the primary colors. An LCD panel uses these three colors to produce color which is why there are three cells per pixel — one cell each for red, green, and blue.

Once the light is passed through the liquid crystal layer and the final polarizing filter it then passes through a color filter so that each cell will then represent one of the three primary colors of light. See Figure 3.

LCD Panel Inside
Figure 3

The three cells per pixel then work in conjunction to produce color. For example, if a pixel needs to be white, each transistor that controls the three color cells in the pixel would remain off, thus allowing red, green and blue to pass through. Your eye sees the combination of the three primary colors, so close in proximity to each other, as white light.

If the pixel needed to be blue, for and area of an image that was going to be sky, the two transistors for the red and green cells would turn on, and the transistor for the blue cell would remain off, thus allowing only blue light to pass through in that pixel.

We hope this straightforward explanation is enough. If you have further questions, please email us at info@theprojectorpros.com.