The computer generally takes the data and process the data and give us information. this information is provided to the users with help of output unit of the computer. The output unit consists of devices which are often called as output devices which are capable of converting the machine understandable format to Human understandable format. Let us discuss some of the output devices are their working ....
Monitor (Visual Display Unit):It is the most commonly used output device. The monitor is a soft copy (means we can modify contents of data and data is temporarily on the screen) output device. A monitor looks like a television and it displays alphanumeric and graphic output. A monitor is also called Visual display unit (VDU)
Types of monitor :
CRT (Cathode Ray Tube ) Monitors:Standard glass-tube televisions and your CRT monitor work quite similarly. A glass cathode-ray tube (1), which contains a vacuum, has three electron guns (2) at its narrow end, each containing an anode and cathode assembly. As you may recall from high-school science, the cathodes emit electrons; the anodes draw the electrons away from the cathodes, focusing and accelerating them into electron beams (3). The deflection yoke (4), around the tube base, precisely manipulates the three beams via electromagnetic force, working with the CRT's circuitry to sweep them across the screen in precise, horizontal lines. Where a beam hits the screen, it causes a red, green, or blue (RGB) phosphor dot (5) to glow; the screen's inner surface is coated with these colored phosphors. (The beams, though colorized in the illustration, are actually invisible.)
The electron guns blaze across the screen, row by row, illuminating phosphors in their wake. Varying the beams' intensity strengthens or weakens the glow from a given phosphor dot; by careful manipulation of every one, the triads and pixels, seen by the eye as single units, create the illusion of different-color dots.
Phosphors don't glow for long, though. Once the guns have scanned the whole screen, they repeat the process—typically, 60 to 80 times a second. (This number is what is known as the refresh rate.) To comprehend the staggering scale of the task: A CRT running at 1,280x1,024 at a 75Hz refresh rate illuminates and re-illuminates nearly 100 million pixels per second.
LCD MonitorsA liquid crystal display or LCD draws its definition from its name itself. It is combination of two states of matter, the solid and the liquid. LCD uses a liquid crystal to produce a visible image. Liquid crystal displays are super-thin technology display screen that are generally used in laptop computer screen, TVs, cell phones and portable video games. LCD’s technologies allow displays to be much thinner when compared to cathode ray tube (CRT) technology.
Liquid crystal display is composed of several layers which include two polarized panel filters and electrodes. LCD technology is used for displaying the image in notebook or some other electronic devices like mini computers. Light is projected from a lens on a layer of liquid crystal. This combination of colored light with the grayscale image of the crystal (formed as electric current flows through the crystal) forms the colored image. This image is then displayed on the screen.
Simple facts that should be considered while making an LCD:
- The basic structure of LCD should be controlled by changing the applied current.
- We must use a polarized light.
- Liquid crystal should able be to control both of the operation to transmit or can also able to change the polarized light.
How LCDs Work?
- LCD’s consumes less amount of power compared to CRT and LED
- LCD’s are consist of some micro watts for display in comparison to some mill watts for LED’s
- LCD s are of low cost
- Provides excellent contrast
- LCD’s are thinner and lighter when compared to cathode ray tube and LED
- Require additional light sources
- Range of temperature is limited for operation
- Low reliability
- Speed is very low
- LCD’s need an AC drive
Liquid crystal technology has major applications in the field of science and engineering as well on electronic devices.
- Liquid crystal thermometer
- Optical imaging
- The liquid crystal display technique is also applicable in visualization of the radio frequency waves in the wave guide
- Used in the medical applications
LED MonitorsLED display refers to the light emitting elements who is composed by the LED LED (light emitting diodes) array, which is directly used as a pixela to emit red, green, and blue light, thereby forming color images, such as traffic lights, outdoor big screen.
The LED display we are talking here should be precisely called as “LED-backlit LCD monitor”, the principle of which is converting the traditional CCFL into LCD backlight source is into LED (light
So far, the advantages of LED backlit display is in the theoretical stage, the display is not as good as what the display maket advocated . The main advantages are: energy saving, ultra-thin, light leakage control is better.
OLED Display:OLED (Organic Light-Emitting Diode), literal translation is “organic light emitting diode” or “organic light emitting display.” Monochrome, multicolor, color OLED device has reached the level of mass production, large-size, full-color device is still in development stage. OLED emits light with the help of current driving the organic thin film, OLED can be thinner, the thinnest panel is only 0.1 millimeters, and the use of different material can be made into any curved shape.
Plasma Display:Plasma display is also a flat display screen, but unlike LCD, LED, plasma screens emit light byitself, rather than relying on a backlight.
The principle is that the mercury vapor or the inert gas is inserted into the vacuum glass tube, after which voltage is applied to, making the gas generating the effect of plasma and emiting ultraviolet light, exciting the phosphor to generate visible light ,taking advantage of how long the light excited is to generate different brightness. The display, each pixel is generated by three different colors (RGB) light emitting plasma body. Since each pixel has its own separate light, it is particularly vivid.
Because of its technical characteristics, the plasma display can be much brighter and can display more colors, Plasma Display with no viewing angle and competitive contrast ratio can create a large area of screen, particularly suited for watching movies. However, plasma screens have image blur when playing a still figure for a long time, brightness will be recessed, but the plasma display generate large amount of heat.