CONTENT Introduction
History
Working Operation
Block Diagaram
Types
Cold Cathode Fluorescent Backlights (CCFL)
LED
Specification
Application
Advantage & Disadvantage
References
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.
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
EDGE 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.
FULL 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.
SPECIFICTION
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.
APPLICATIONS
Smartphone
Tablet Pc
Ebook
Ultrabook/Notebook
Video Camera
Media Player
Portable Game
GPS
Automotive
LED TV
Lighting
Smart Metering
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.
More Accurate Color:
LED backlit TVs can offer richer color than LED panels. This can be accomplished through slightly modifying the color of the white light emitted by the LEDs to compensate for the LCD's shortcomings. A more advanced solution comes in some Sony Bravia models, which use a multi-colored backlight to reinforce the image on screen.
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.
INSTRUMENTATION & CONTROL
1ST SEM
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