LCD stands for Liquid Crystal Display. It is a flat panel display technology, mainly used in TVs and computer monitors, nowadays it is used for mobile phones also. These LCDs are completely different from that old CRT displays, it uses liquid crystals instead of cathode ray in its primary form of operation.
In LCD display, it consists of millions of pixels made of crystal and arranged in a rectangular grid. In LCD it has backlights that provide light to each pixel. Each pixel has a red, green, and blue (RGB) sub-pixel that can be turned on or off. When all of the sub-pixels are turned off, then it’s black and when all the sub-pixels are turned on 100%, then it’s white.
LCD is a combination of two states of matter, the solid and the liquid. The solid part is crystal and this liquid and crystal together make the visible image. LCD consists of two layers which are two polarized panels- filters and electrodes. LCD screen works by blocking the light rather than emitting the light. There are two types of pixel grids in LCD:
- Active Matrix Grid– It is a newer technology. In smartphone with LCD display uses this technology.
- Passive Matrix Grid– It is an older technology. Some older devices used this technology.
The LCD display was first built in the year 1964 in RCA Laboratories by George Heilmeier who was an electrical engineer in the RCA lab.
At first in the year 1888, liquid crystal was discovered by Friedrich Reinitzer by extracted cholesterol from carrots, who was an Austrian botanist. In that time liquid crystal was used in research and experimental works. Then by the year 1936, liquid crystal was used in a practical application and known as Liquid Crystal Light Valve which is used in wireless telegraphy.
Then in the year 1962, a researcher of RCA Richard Williams generated some patterns in a thin layer of liquid crystal material by applying voltage on it, which is known as electro-optical effects. After all these things finally in 1964 LCD was invented.
The first modern LCD was produced in the year 1972, by International Liquid Crystal Company (ILIXCO) owner James Fergason. This LCD was made using passive grid technology. In the year 1995 Hitachi and NEC were the first manufacturers of active matrix LCDs. These LCDs are based on IPS(In Plane Switching) technology. After all this, by the year 1996 SAMSUNG, TOSHIBA has came to market.
Main characteristics of LCD are:
- Voltage: 3V to 12V
- Operating temperature: Normally it ranges from to , but for extreme cases it varies from to .
- Frequancy: 30Hz to 60 Hz
- Average Current consumption: 1.2A to 6A
- Opening Time: 100 ms
Also LCD has other characteristics in terms of many areas, that are
- Resolution: LCD is made up of liquid crystal, which is neither liquid nor solid, and this thing reflects the light in a well-formed way, lights enter into the crystal and reflect very clearly. So the image made with this liquid crystal is very accurate. LCD is a Digital display, which addresses each individual pixel using a fixed matrix of horizontal and vertical dots. LCD scales the image according to the resolution the device provided. So the quality of the image is not degraded.
- Brightness: Brightness means the light provided by the LCD, which is nothing but the intensity of visible light, it is measured using nits. Nits is defined as one candela per square meter. In LCD brightness is very much accurate for the good resolutions and pixels.
- Contrast Ratio: It is the ratio of the brightest color and the darkest color for a particular position of the screen provided by the display. To calculate contrast ratio(CR) see the below formula:
Typically the ratios of modern monitors are 1000:1 and TVs are 4000:1.
- Response Rate: Response Rate is high in LCD, it means the time required for changing colors of the pixels is very much less, so that the refresh rate is very high in LCD than CRT. There is no lagging between the pixels when the image is changed.
Advantages of LCD :
- The main advantage of LCD is, it has low in cost and energy efficient and very less power consumption.
- LCD is thinner and lighter and very flexible.
- LCD provides excellent contrast, brightness and resolution, so the picture quality is very clear like a crystal.
- Radiation of LCD monitors are much less than CRT monitors
- LCDs can be suitable with CMOS integrated circuits so that making of LCD is very easy.
- It gives perfect sharpness at the native resolution
- Zero geometric distortion at the native resolution of the pane
- It provides various conveniences like portability as compared to previous technology based screens.
Disadvantages of LCD :
- LCD require additional light sources for lighting the pixels, so if the light source is destroyed then the LCD is not providing any image on the display.
- LCD is less reliable display.
- The image visibility depends on light intensity
- The aspect ratio and resolution are fixed for LCD.
- LCD has an irregular intensity scale and it produce lower than 256 discrete intensity levels.
- In LCD color saturation is reduced at the low intensity level due to poor black-level.
- LCD provide limited viewing angle, it effects the brightness. if we are watching the screen by an angle then the color of the image is changed in our eyes.