Laser, led,lcd display

What’s So Different?
Incandescent Lamp only around 10% of the energy is
used to make visible light.

INTRODUCTION
A light-emitting diode (LED) s are special diodes
that emit light when connected in a circuit.
 Amount of light output is directly proportional to
forward current

SC materials – Gallium Phosphide (red or green)
Gallium arsenide Phosphide(red or
yellow)
Gallium arsenide ( infrared)
Gallium nitrite (blue)

Contd..• The negative side of an
LED lead is indicated in two
ways: 1) by the flat side of
the bulb, and 2) by the
shorter of the two wires
extending from the LED. The
negative lead should be
connected to the negative
terminal of a battery .

COLOUR OF LED
The colour of the light (corresponding to the energy
of the photon) is determined by the energy gap of the
semiconductor.
LEDs are designed to operate with no more than 30–
60 milliwatts of electrical power.

ADVANTAGES
Lower energy consumption
Longer lifetime
Improved robustness
Smaller size
Faster switching

DISADVANTAGES
 LEDs powerful enough for room lighting and are
relatively expensive.
It requires more precise current and heat
management than compact fluorescent lamp sources
of comparable output.

APPLICATIONS
Light-emitting diodes are used as
Low current LED –low power dc circuits,
telecommunication indicator, portable equipment,
keyboard indicator
Automotive lighting
Traffic signals
Infrared LEDs are also used in the remote control
units of many commercial products including
televisions, DVD players, and other domestic
appliances.

How LED Lighting Distinguishes
Every Application Area
LEDs in Retail Environments
provide a wide range of effects – from the strikingly
dramatic to the intriguing and inviting – that
contribute to the total shopping experience.
highlight a product, create drama and interest, but it
can also reflect mood, helping create the perfect
environment for the shopping experience.

LEDs in Office Environments
uniform level of illumination throughout.
Reflections on computer screens can prove tiring as
the day draws on, and as concentration drops, so does
efficiency.
 making people feel more comfortable at work and
stimulating their performance – but also considerable
energy and maintenance cost reductions.

LEDs in Hospitality Environments
Lighting a hotel or restaurant is a complicated
business.
Hotels, for example, need to have lighting 24/7 – in
corridors and hallways, for example, or in reception.
Yet the lighting must also be adaptable, capable of
creating a wide range of moods to make the guest feel
welcome, safe and comfortable.
LED solutions can make guests feel comfortable, at
home. And do it while offering enormous savings in
maintenance and energy-costs. LED solutions can
create an ever-changing palette of moods, each tailor-
made for a specific moment, a specific use.
low maintenance such systems required thus greatly
reducing running costs.

LED in Outdoor Environments
The needs of urban lighting are changing.
creating flexible ambiances that could, for example,
change with the weather or the season, and provide
an extra festive color on public holidays.
energy consumption that is only a fraction of
conventional lighting techniques.

How an LCD works
An array of Liquid Crystal segments
–When not in an electrical field, crystals are organized in a
random pattern
–When an electric field is applied, the crystals align to the
field
–The crystals themselves do not emit light, but ‘gate’ the
amount of light that can pass through them
•Crystals aligned perpendicular to a light source will prevent
light from passing through them
Each LCD segment is aligned with an electric field
A light source (backlight) is needed to drive light through
the aligned crystal field

Passive LCD panels
Active LCD
panels

Passive LCD panels
–Consists of a grid of row and columns electrical
signals
–Columns and rows connect perpendicularly to every
segment in the LCD
•Columns and rows are multiplexed to many different
segments
–An IC controls which column and row are selected to
enable or disable the segment at the row/column
intersection
–A small bias is applied to the row and column to
generate a field at the intersection
•No charge is stored at the segment
•It may take multiple passes to correctly align the field
to the desired value

Active LCD panels
–Consists of a grid of row and columns electrical
signals
–Columns and rows connect perpendicularly to a
active device (transistor) for every segment in the
LCD
•Columns and rows are multiplexed to many different
segments
–An IC controls which column and row are selected
to enable or disable the segment at the row/column
intersection
–The selected row and column enable the transistor
•Charge is stored at the transistor
•One pass will set the aligned state of the transistor
(although it may still take a little time for all the

Construction
two glass plates with some liquid crystal material
between them
Types
Dynamic scattering LCD
Field effect LCD

Dynamic scattering LCD
Transmittive type cell
Reflective type cell

LASER INTRODUCTION
Light Amplification by Stimulated Emission of Radiation
 The Laser is a source of highly directional,
monochromatic, coherent light.
The unique property of laser is that its light waves travel very
long distances with every little divergence
Laser diode is similar in principle to an LED.
Case of a conventional e source of light, the light is emitted
in a jumble of e separate waves that cancel each other at
random and hence can travel very short distances only.
concentration of its energy to extremely high intensities, the
intensity remaining almost constant over long distances
because of low divergence.

Types
Surface emitting laser diodes
Edge emitting laser diodes

ADVANTAGES
The semiconductor laser differs from other lasers (solid,
gas, and liquid lasers):
 small size (typical on the order of 0.1 × 0.1 × 0.3 mm3)
 high efficiency
 the laser output is easily modulated at high frequency
by controlling the junction current
 low or medium power (as compared with ruby or CO2
laser, but is comparable to the He-Ne laser)
 particularly suitable for fiber optic communication

COMPARISION
Laser Diode
 Stimulated radiation
 narrow line width
 coherent
 higher output power
 a threshold device
 strong temperature
dependence
 higher coupling
efficiency to a fiber
LED
 Spontaneous radiation
 broad spectral
 incoherent
 lower output power
 no threshold current
 weak temperature
dependence
 lower coupling
efficiency

APPLICATIONS
 Optical-fiber communication
 Video recording
 Optical reading
 High-speed laser printing
 High-resolution gas spectroscopy
 Hologram scanners

MIND MAP
36
LCD LED Laser
construction
applications Advantages

Summary
LED,LCD, LASER
Definition
Construction
Principle
Advantages
Application

Multiple choice question
 The Laser operates under a ___________ process.
A) stimulated emission b) unstimulated emission
c) Emission d) discharge
 Which is not the application of laser diode
a) Optical-fiber communication
b) Video recording
c) Optical reading
d) low -speed laser printing

Laser, led,lcd display

More Related Content

What's hot (20)

Similar to Laser, led,lcd display (20)

More from Rajendran (20)

Recently uploaded (20)

Laser, led,lcd display