How LCDs Work

Liquid crystal displays, or LCDs, are a type of display commonly used in electronic devices. Your digital clock, microwave oven, CD player, calculator and laptop computer probably all have LCDs. LCDs are lighter weight, smaller and less expensive to manufacture than many display technologies. But, how does an LCD actually work?

A liquid crystal display uses a unique material called liquid crystal; it acts like a liquid in the way it moves, but also has properties of a solid in the way its molecules are oriented. The molecules in liquid crystal twist and can be changed by polarized light transmitted into it. Liquid crystal is highly temperature sensitive and becomes fully liquid with the addition of only a small amount of heat. Liquid crystal is transparent.

In an LCD, the liquid crystal is sandwiched between 2 layers of polarizing material. This polarizing material has molecules in it that align with one another; it allows light to pass through it only in the direction the molecules are not aligned. The light that passes through the polarizing material is considered polarized. Light passes through the first of the polarizing filters and into the liquid crystal. In the liquid crystal, the light is changed to match the orientation of the molecules surrounding it. If the light is aligned with the second polarizing layer when it reaches it, it will pass through without additional changes.

Electrical current can have an effect on liquid crystal. So, if an electrical charge is applied to the liquid crystal in an LCD, it can change the orientation of the molecules again. If it changes it so the light cannot pass through the top polarizing layer, that portion of the LCD screen will remain dark. The use of light and dark in the display is what the LCD uses to display images.

LCDs do not emit any light. In order for an LCD to be visible, it needs a light source. Sometimes LCDs use reflected light from outside sources. Other times, they are backlit with additional lighting devices like fluorescent bulbs.

Liquid crystal displays can be monotone or color. Traditional monotone LCDs use light and dark gray to display images. Color LCDs can use passive matrix technology, which is older and less expensive or active matrix. Active matrix, which incorporates transistors and capacitors into the display, produces sharp, clear images and is considered visually comparable to CRT display technology.

In color LCDs, there are red, green and blue filters that allow the colors to be displayed in subpixels within each pixel. The amount of voltage applied to each subpixel affects the intensity of the color displayed and the combination of the subpixel colors and intensities create all of the possible visible colors on the display screen.

LCDs can actually be built with an inverse effect as well. In these arrangements, when no electricity is applied, light cannot pass through.

There are many different types of liquid crystal and different components may be used to control them. Liquid crystal technology is constantly being improved; as quality improves and the cost is lowered, larger LCD screens will become common and new uses for LCDs will become apparent.

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