GUJARAT TECHNOLOGICAL UNIVERSITY BIRLA VISHVAKARMA MAHAVIDYALAYA V.V.NAGAR

CONTENT  Introduction  History  Working Operation  Types  Specification  Application  Advantage & Disadvantage

INTRODUCTION  The LED TV is a more advanced version of the LCD TV. While both types of TV on LCD technology and have flat- panel designs.  "LED TVs are slimmer, brighter, and more detailed than your traditional LCD TV." LED TVs function by illuminating LCD panels with LED backlighting. However, not all LED TVs utilize the same type of LED backlighting.

HISTORY  From the early 1900s, scientists have been discovering ways to generate light from various materials. In 1907, Henry Joseph Round discovered that light could be generated from a sample of Silicon Carbide (SiC). For the next 50 years, scientists continued to discover the light emitting properties that exist with some compounds. In the 1950s, studies around the properties of Gallium Arsenide (GaAs) paved the way for the first official LED discoveries that soon followed.

WORKING PRINCIPLE  A semiconductor with extra holes is called P- type material, since it effectively has extra positively-charged particles. Electrons can jump from hole to hole, moving from a negatively-charged area to a positively- charged area. As a result, the holes themselves appear to move from a positively- charged area to a negatively-charged area.  A diode comprises a section of N-type material bonded to a section of P-type material, with electrodes on each end. This arrangement conducts electricity in only one direction.

 When no voltage is applied to the diode, electrons from the N-type material fill holes from the P- type material along the junction between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and charge can't flow. At the junction, free electrons from the N-type material fill holes from the P-type material. This creates an insulating layer in the middle of the diode called the depletion zone.

TYPES  A LCD screen is composed of 2 parts, the actual liquid crystal display and a light source at the back of the screen (called backlight). A light diffuser is placed between the backlight and the LCD screen to uniform the source of light equally across the screen.  LCD stands for “liquid crystal display” and technically, both LED and LCD TVs are liquid crystal displays.

 The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light.  So really, LED TVs are a subset of LCD TVs.

 There are 2 main types of backlights used in LCD screens. 1. CCFL 2. LED

CCFL  LCDs with CCFL backlight are on their way out of the market. Manufacturers are now only producing them for their lower end and smaller models. They are getting replaced by LED TVs. They have the same screen but have LED lights instead of a CCFL tube for the backlight

 LED, which stands for “light emitting diodes,” differs from general LCD TVs in that LCDs use fluorescent lights while LEDs use those light emitting diodes.  Also, the placement of the lights on an LED TV can different.  The fluorescent lights in an LCD TV are always behind the screen.  But, On an LED TV, the light emitting diodes can be placed either behind the screen or around its edges.

 The difference in lights and in lighting placement has generally meant that LED TVs can be thinner than LCDs, although this is starting to change.  It has also meant that LED TVs run with greater energy efficiency and can provide a clearer, better picture than the general LCD TVs.  Because of difference in lights and lightning placement there are two types  EDGE LIT  FULL ARRAY LIT

E DGE LIT  This is the most common method for LED TVs.

E DGE LIT  In an edge lit LED screen, the LEDs are placed at the peripheral of the screen.  Depending on the television, it can be all around the screen or only on the sides or the bottom.  This allows the screen to be very thin. However, it can cause some spots on the screen to be brighter than others, like the edges.

F ULL ARRAY

 This method is considered the best LED backlight type, but can only be found on a very limited number of models.  In a full array LED screen, the LEDs are distributed evenly behind the entire screen. This produces a more uniform backlight and it provides a more effective use of local dimming, where it can change the luminosity of only a specific part of the screen.

S PECIFICTION  Cost : As per size of TV(almost 20k -70k)  Size : available in 32”,42”,…….  As per the market survey LG, SAMSUNG, SONY,TOSHIBA,PANASONIC are making LED TV.

A PPLICATIONS  Smartphone  Tablet PC  Ultrabook/Notebook  Video Camera  LED TV  Lighting

ADVANTAGES  Power Savings: LED backlit TVs are more power efficient than traditional LCD TVs. Although regular LCDs are relatively efficient, LED cells simply produce more light per watt than fluorescents. This can result in a power savings of approximately 40 percent.  Better Contrast: Some LED backlit TVs are capable of generating better contrast through the use of local dimming. Local dimming is when LEDs behind dark parts of the picture are either dimmed or left off. Doing this can increase the appearance of contrast in the image.

Smaller Size:  Because LEDs are smaller than CCFL tubes, LED TVs can be thinner than traditional LCD TVs. In addition to this, TVs that are edge lit place their LED backlights on the side, making it possible for them to be even thinner than regular LCDs.

DISADVANTAGE  Water - Water can easily damage LEDs.  Cost - cost of its is very high.

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