Wikijunior:How Things Work/LCD Display

Who invented it?

George Heilmeier invented the LCD display. He was an American engineer who died in 2014, aged 77.

How does it get power?

Electricity is used to power an LCD display. It is used to provide power for backlighting and to control the configuration of the display itself.

How does it work?

LCD stands for Liquid Crystal Display. As the name suggests, it is a display that is made using liquid crystals. Liquid crystals are used to control the passage of light through the display screen. Where light is allowed through, the screen appears bright and where light is blocked the screen appears dark.

The liquid crystals in their natural state are in a twisted but predictable form. They are positioned between a pair of polarizing filters in the display. Polarizing filters can be thought of as a grill that only allows light waves in one orientation to pass through. The two polarizing filters in an LCD display are aligned so their grills are in the same direction. Light passing through the first filter is polarised. As the polarized light passes along the liquid crystals it is directed by the crystals and emerges parallel to the second set of polarizing filters. Because the light waves are parallel to the polarizing filter, they are allowed through.

When a voltage is applied to the liquid crystals, they untwist slightly, changing the orientation of the polarized light so that it no longer emerges parallel to the second polarizing filter. This causes the light to be blocked by the filter, so that the screen at that point appears dark.

LCD displays consist of separately controlled sections of liquid crystals. These can number from just a few (as in a watch) to many thousands or millions (as in a computer display or television).

How dangerous is it?

Unless seriously damaged, LCD screens are safe, apart from the usual risk of an electric shock that comes with any electric machine. Unless you swallow the screen or try to take it apart, they are basically completely safe.

What does it do?

It shows information including images and motion pictures on a screen. Many electronic device's screens are LCD screens.

How does it vary?

Some displays rely on natural (or ambient) light to provide the illumination for the screen, and usually have a reflective surface at the back of the display to reflect any natural light entering the display back through the display to its surface.

Other types of displays have backlighting, which is where there is an electrical light source behind the display that illuminates the display where light is permitted through.

The original LCDs only had two different 'colours', one dark and one light, with only two intensities (on and off). The colours were usually black and light grey (the colour produced by ambient light moving through the display). More recently, LCDs with variable intensities have been produced, where the voltage applied to each liquid crystal can be controlled so that the amount of untwisting is varied and so the amount of light allowed through is varied.

Colour LCDs have also been developed (such as those used in colour televisions). These consist of millions of dots (or pixels), each of which has several coloured sections which can individually be turned on at varying intensities. Because the pixel sections are so small and so close together, our vision interprets this combination of colours as a single shade. The display is therefore able to represent millions of possible colours.

How has it changed the world?

LCD uses very low power compared to its main alternatives. Thus its helps to save power and still provides good picture quality. Many computers, phones and televisions use LCD screens. There is a good chance you are reading this on a screen using an LCD display!

What idea(s) and/or inventions had to be developed before it could be created?

Without Friedrich Reinitzer's discovery of liquid crystals, it would be impossible to make a Liquid Crystal Display.