Display devices

 Topic Outline

Display devices
Types
  • Cathode Ray Tube
  • Flat Panel Display
    • Emissive Display
      • LED
      • OLED
      • Gas Plasma
    • Non-Emissive Display
      • LCD



A display device is an output device. It is used to represent information in the form of text, graphics, images, and video. The display for a desktop computer is a monitor. Mobile computers and devices integrate the display in the same physical case. Some displays have touch screens such as mobile phones and laptops etc. The output displayed by a display device is called soft copy. Display devices are available in different sizes.

For example

When we write any document on the computer, it is a soft copy of the document. When we get a print of this document, it is a hard copy of the document.

Types

Types of display devices are as follows.

(1) Cathode Ray Tube

A cathode-ray tube creates an image on the screen by using a beam of electrons. Cathode ray tube consists of one or more guns. These guns fire a beam of electrons inside the screen. The monitor screen is coated with tiny phosphor dots from inside. The beam of electrons continuously fells on the surface of the screen and every beam fall takes only a fraction of a second.

In the color monitor, the Cathode ray tube consists of three guns. These guns produce red, green, and blue colors. Other colors are produced with a combination of these colors.

(2) Flat panel display

  • It uses electronically charged chemicals or gases between thin panes of glass.
  •  Flat panel display take less space. 
  • Flat panel displays are lightweight and consume less power than Cathode ray tubes.
  • It is more expensive than a Cathode ray tube.
  • Flat panel displays do not emit harmful radiation.
  • It uses digital signals to display images. 
  • Flat panel displays are available in different sizes.

Example

Tv monitors, laptops, computers, calculators, etc.

  • Emissive Display 

Emissive displays are devices. It converts electrical energy into light. For example, LED, OLED, and Gas plasma.

    • Light Emitting Diode (LED)
  • Display that uses light-emitting diode for backlight is called light-emitting diode display. 
  • Light-emitting diode consumes less power than liquid crystal display.
  • Light-emitting diode is thinner, lighter, and brighter than liquid crystal display.
  • Light-emitting diode can be more expensive than liquid crystal display.

For example

The laptop screen and mobile devices use LED backlight technology.

    • Organic Light-Emitting Diode (OLED)

It uses emissive organic material to display brighter images. When an electric current is applied organic light-emitting diode use layers of organic material that emits visible light. An organic light-emitting diode is brighter, thinner, and sharper than a liquid crystal display. Organic light-emitting diodes have a wider viewing angle than liquid crystal displays.

    • Gas Plasma Display

It uses gas plasma technology. This technology uses layers of gas between two glass plates. When voltage is applied, gas releases ultraviolet light. Due to this ultraviolet lights pixels on the screen glow. 

Plasma display provides richer colors than liquid crystal display monitor.

 It is more expensive than a liquid crystal display.

  • Non-Emissive Display

Nonemissive displays use optical effects to convert sunlight or light into graphics patterns. For example LCD.

    • Liquid Crystal Display (LCD)

It uses charged liquid crystal between two sheets of material such as glass to light up the appropriate pixels to form the image on the screen. LCD uses a cold cathode fluorescent lamp as the light source. It is also known as the backlight. 

  • It provides a sharper image than a cathode-ray tube.
  • Liquid crystal display emits less radiation.
  • Liquid crystal display also requires less power and takes less space than the cathode-ray tube.

Flat-panel screens are active and passive matrices.

Active Matrix Display

In this matrix, each pixel on the screen is controlled by its own transistor. Active matrix display is brighter and sharper than passive screen. It is more expensive and requires more power. It is also called a thin-film transistor.

Passive Matrix Display

In this matrix, two transistors control a whole row or column of pixels at the same time. It is less expensive and uses less power than an active matrix display. The clarity of the image is not sharp in the passive matrix. It is also called a dual scan monitor.


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