LITERATURE REVIEW

JOURNAL 4

LCD DISPLAY

LCD (liquid crystal display) is the technology used for displays in notebook and other smaller computers. Like light-emitting diode (LED) and gas-plasma technologies, LCDs allow displays to be much thinner than cathode ray tube (CRT) technology. LCDs consume much less power than LED and gas-display displays because they work on the principle of blocking light rather than emitting it. 

An LCD is made with either a passive matrix or an active matrix display display grid. The active matrix LCD is also known as a thin film transistor (TFT) display. The passive matrix LCD has a grid of conductors with pixels located at each intersection in the grid. A current is sent across two conductors on the grid to control the light for any pixel. An active matrix has a transistor located at each pixel intersection, requiring less current to control the luminance of a pixel. For this reason, the current in an active matrix display can be switched on and off more frequently, improving the screen refresh time (your mouse will appear to move more smoothly across the screen, for example).

Some passive matrix LCD's have dual scanning, meaning that they scan the grid twice with current in the same time that it took for one scan in the original technology. However, active matrix is still a superior technology.

Advantages: 

• Very compact, thin and light, especially in comparison with bulky, heavy CRT displays. 
• Little heat emitted during operation, due to low power consumption. 
• No geometric distortion. 
• The possible ability to have little or no flicker depending on backlight technology. 
• Sharp image with no bleeding or smearing when operated at native resolution. 
• Can be made in almost any size or shape. 
• Many LCD monitors are powered by a 12 V power supply, and if built into a computer can be powered by its 12 V power supply. 

Disadvantages: 

• Limited viewing angle in some older or cheaper monitors, causing color, saturation, contrast and brightness to vary with user position, even within the intended viewing angle. 
• Uneven backlighting in some monitors (more common in IPS-types and older TNs), causing brightness distortion, especially toward the edges ("backlight bleed"). 
• Black levels may not be as dark as required because individual liquid crystals cannot completely block all of the backlight from passing through. 
• Dead or stuck pixels may occur during manufacturing or after a period of use. A dead pixel will glow with color even on an all-black screen. 
• Loss of brightness and much slower response times in low temperature environments. In sub-zero environments, LCD screens may cease to function without the use of supplemental heating. 
• Loss of contrast in high temperature environments.

Credit to : Prajapati Dipali, K., Raj Roshani, D., Patel Komal, C., & Hilali Marhaba, A. ( 2014). Automatic Gate Opening System For Vehicles With RFID or Password.