Liquid Crystal Diode (LCD) technology could be a variety of lighting utilized in computer monitors, laptops, and televisions, together with various other types of home and outdoor lighting. It uses cold-cathode fluorescent lights referred to as CFL lights to illuminate the screen for viewing graphics, text, and video. LCD contains a chilly cathode and twisting crystal lights because of the defining technology.
The LED is a PN-junction diode that emits light when an electric current passes through it in the forward direction. In the LED, the recombination of the charge carrier takes place. The electron from the N-side and the hole from the P-side are combined and give the energy in the form of heat and light. The LED is made of semiconductor material which is colorless, and the light is radiated through the junction of the diode.
Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared (IR) light. Infrared LEDs are employed in remote-control circuits, like those used with a large style of consumer electronics. The primary visible-light LEDs were of low intensity and limited to red. Modern LEDs are available across the visible, ultraviolet (UV), and infrared wavelengths, with the high light output.
Advantage of LED:
- LEDs have a very long life.
- It requires low maintenance.
- LED doesn’t produce heat.
- LED is highly efficient.
Disadvantage of LED:
- It is more costly.
- It has a restricted viewing angle.
LED monitors do not use cold-cathode technology and fluorescent technology. Instead, light diodes illuminate the screen in one of two different ways, or a combination of both. White LED lights are clustered around the rim of the screen and diffuse evenly, called edge lighting. LED lights are also spaced evenly behind the screen, and they are either not controlled or are controlled with a “local dimming” option. If we are looking for an LED monitor, look for this local dimming on/off option.
LEDs are utilized in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes, lighted wallpaper, horticultural grow lights, and medical devices. Unlike a laser, the light emitted from an LED is neither spectrally coherent nor even highly monochromatic. However, its spectrum is sufficiently narrow that it appears to the human eye as a pure (saturated) color. Also unlike most lasers, its radiation isn’t spatially coherent, so it cannot approach the very high brightness’s characteristic of lasers.
The working of the LED depends on quantum theory. The quantum theory states that when the energy of electrons decreases from the higher level to the lower level, it emits energy in the form of photons. The energy of the photons is equal to the gap between the higher and lower level.
The LED is connected in the forward-biased, which allows the current to flows in the forward direction. The flow of current is because of the movement of electrons in the opposite direction. The recombination shows that the electrons move from the conduction band to the valence band and they emit electromagnetic energy in the form of photons. The energy of photons is equal to the gap between the valence and the conduction band.
LEDs are made in numerous packages for various applications. One or some LED junctions is also packed in one miniature device to be used as an indicator or pilot light. An LED array may include controlling circuits within the identical package, which can range from a straightforward resistor, blinking or color-changing control, or an addressable controller for RGB devices. Higher-powered white-emitting devices are going to be mounted on heat sinks and can be used for illumination. Alphanumeric displays in dot matrix or bar formats are widely available. Special packages permit the connection of LEDs to optical fibers for high-speed digital communication links.
The LEDs are very economical and giving a high degree of reliability because they are manufactured with the same technology as that of the transistor. These are operated over a wide range of temperatures say 0° – 70°. Also, it is very durable and can withstand shock and variation. These have high efficiency, but they require moderate power for operation. Typically, the voltage of 1.2V and the current of 20mA are required for full brightness. Therefore, it is used in a place where less power is available.