Science for Everyone: LCD, LED

My Lord, What is the difference between LCD and LED?

In Bloomsbury Dictionary of ‘Science for Everyone’, LCD and LED are described in the following manner: LCD AND LED are the two principal methods of forming number sand letters on instruments such as calculators and digital watches. A basic pattern of seven bars is used to form the digits 0 to 9 and several letters. To form other letters and symbols, more than seven bars are required.

In the LED (light-emitting diode), the bars are made of a substance that permits an electric current to flow through in one direction only. A substance used in this way is called a diode. As the current flows, the diode gives off red, blue, yellow, or other coloured light, depending on the compound of which it is made. For example, gallium phosphide (GaP) emits a green glow. Electric circuits in the instrument selectively turn on the current to the bars to form the various numbers and letters.

In the LCD (liquid crystal display), the bars are made of liquid crystals. These are a kind of hybrid material, not quite a liquid and not quite a solid. They can’t be poured readily, as with liquids, nor are their molecules locked in place, as with true solids. But the molecules can be rotated slightly by an electric current. When no current flows, the bars are not noticeable, because they reflect light to the same extent as the rest of the display surface. But when a current flows through a bar, its molecules rotate and its ability to reflect light is reduced. That bar appears darker than the area around it and forms part of a number or letter.

– Hon’ble Justice A.K. SkiriSecure Meters Ltd. v. Commissioner of Customs, 2015 (6) SCALE 48.

LED Watch