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)

Anatomy of an LED

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.

ADVANTAGESLower energy consumptionLonger lifetimeImproved robustnessSmaller sizeFaster 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 asLow 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 AreaLEDs 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 worksAn 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 themEach LCD segment is aligned with an electric fieldA light source (backlight) is needed to drive light through the

aligned crystal field

Twisted Nematic (TN) Displays

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 crystals to align)

–A stronger backlight is needed than a passive displayTFT

Construction

two glass plates with some liquid crystal material between them

Types Dynamic scattering LCDField effect LCD

Dynamic scattering LCD

Transmittive type cellReflective type cell

Reflective type cell

Field effect LCD

Field effect LCD

Advantages

Disadvantages

Application

LASER INTRODUCTIONLight 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 diodesEdge 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

COMPARISIONLaser 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

Draw mindmap

MIND MAP

36

LCD LED Laser

construction

applications Advantages

Summary LED,LCD, LASERDefinitionConstruction PrincipleAdvantages 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 diodea) Optical-fiber communication b) Video recording c) Optical readingd) low -speed laser printing