V.S.ARJUN LED

7/30/2019 V.S.ARJUN LED

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LIGHT EMITTING DIODES

Presentation by V.S.ARJUN


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A light emitting diode (LED) is essentially a PN junctionopto-semiconductor that emits a monochromatic (single color) lightwhen operated in a forward biased direction.

LEDs convert electrical energy into light energy. They arefrequently used as "pilot" lights in electronic appliances to indicatewhether the circuit is closed or not.

SYMBOL


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How Does A LED Work? (1/2)

When sufficient voltage is applied to thechip across the leads of the LED, electrons canmove easily in only one direction across thejunction

between thepand nregions.

In the p region there are many morepositive than negative charges.

When a voltage is applied and the currentstarts to flow, electrons in the n region havesufficient energy to move across the junction intothep region.


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How Does A LED Work? (2/2)

Each time an electron recombineswith a positive charge, electric potentialenergy is converted into electromagneticenergy.

For each recombination of a negativeand a positive charge, a quantum ofelectromagnetic energy is emitted in the

form of a photon of light with a frequencycharacteristic of the semi-conductor material(usually a combination of the chemicalelements gallium, arsenic and phosphorus)..


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About LEDs (1/2)

The most important part of a light emitting diode (LED)is thesemi-conductor chip located in the center of the bulb as shown at theright. The chip has two regions separated by a junction. Thep regionis dominated by positive electric charges, and the n region isdominated by negative electric charges. Thejunctionacts as a barrierto the flow of electrons between the pand the n regions. Only whensufficient voltage is applied to the semi-conductor chip, can thecurrent flow, and the electrons cross the junction into thep region.


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Light-emitting diodes


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Testing LEDs

Never connect an LEDdirectly to a battery or powersupply! It will be destroyed almostinstantly because too much current

will pass through and burn it out.

LEDs must have a resistorin series to limit the current to asafe value, for quick testing

purposes a 1k resistor is suitablefor most LEDs if your supplyvoltage is 12V or less.

Remember to connect the

LED the correct way round!


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How Much Energy Does an LED Emit?

The energy (E) of the light emitted by an LED is related to theelectric charge (q) of an electron and the voltage (V) required to light theLED by the expression: E = qVJoules.

This expression simply says that the voltage is proportional tothe electric energy, and is a general statement which applies to anycircuit, as well as to LED's. The constant q is the electric charge of asingle electron, -1.6 x 10-19Coulomb.


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CB

VB

When the electron fallsdown from conductionband and fills in a holein valence band, thereis an obvious loss ofenergy.

The question is;where does that energy go?


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In order to achieve a

reasonable efficiency

for photon emission,the semiconductor

must have a direct

band gap.

CB

VB

The question is;

what is the mechanism

behind photon emission in LEDs?


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For example;

Silicon is known as an indirect band-gap

material.

as an electron goes from the bottom of the

conduction band to the top of the valenceband;

it must also undergo a

significant change in

momentum.

CB

VB

What this means is that

E

k


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As we all know, whenever something changes

state, one must conserve not only energy, but alsomomentum.

In the case of an electron going from conductionband to the valence band in silicon, both of thesethings can only be conserved:

The transition also creates a quantized

set of lattice vibrations,

called phoTons, or "heat.


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Photons possess both energy and momentum.

Their creation upon the recombination of an electronand hole allows for complete conservation of both

energy and momentum.

All of the energy which the electron gives up in going

from the conduction band to the valence band (1.1

eV) ends up in photons, which is another way of

saying that the electron heats up the crystal.


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Thus, for a direct band gap material, the excess

energy of the electron-hole recombination can either

be taken away as heat, or more likely, as a photon of

light. This radiative transition then

conserves energy and momentum

by giving off light whenever anelectron and hole recombine. CB

VB

This gives rise to

(for us) a new typeof device;

the light emitting diode

(LED).

M h i b hi d h t i i i


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Mechanism is injection

Electroluminescence.

Luminescence

part tells us that we are producing photons.

Electro part tells us that

the photons are being produced

by an electric current.

e-

Injection tells us that

photon production is by

the injection of current carriers.

Mechanism behind photon emission in

LEDs?

e-


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Producing photon

Electrons recombine with holes.

Energy of photon is the energy ofband gap.

CB

VB

e-

h


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What is LED?

LED - Light Emitting Diode

A semiconductorcomponent similar totransistor or integrated

circuit

Electrical current throughthe semiconductor chipproduces light

Semiconductor materialsused, define the colour oflight produced


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Benefits of LED

Shock and vibration proof

Small dimensions

Lightweight Virtually no heat generation

Accurate and well controlled beam spread


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Key features of LED

Longer lasting

Reduced maintenance cost

More energy efficient

Better design flexibility

Vivid colors

High reliability

Environmentally friendly

They are suitable at high operating speeds


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LED vs. CFL vs. Incandescent Lamps

Incandescent Lamps

90% of electricity used is spent producing heat, not light

Rapidly being replaced by CFLs for lesser bills and environment friendliness

Compact Fluorescent Lamps (CFL)

75% less electricity needed to produce same amount of light as an incandescentlamp

Current estimated sale, of one brand just in Gurgaon, is around one lakh units permonth

Light-emitting Diodes (LED)

15-20% less electricity needed to produce same amount of light as a CFL

Making a slow but steady entry in the market of lighting

Opportunities exist in way too many industries

Currently hot for home decor; Corporate office lighting space hugely untapped

More environment friendly than CFLs


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Why LED?

Energy Efficient, up to 90% more efficient

than traditional lighting sources

Long life span, up to 100,000 hours

Variety of color options

Low operation costs

No UV radiationNo mercury

Instant on, no start-up time

Silent operation

Reduces Carbon Footprint


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Carbon Footprint: comparison chart

Lamp Wattage Operation kWh/year CO2 emission

Incandescent 100W 12hr./day 400kWh 840 lbs

Fluorescent 30W 12hr./day 113kWh 237 lb

Halogen 50W 12hr./day 187kWh 393 lb

HID 300W 12hr./day 800kWh 1,680 lb

LED 3W 12hr./day 12kWh 26 lb


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Materials for visible wavelength LEDs

We see them almost everyday, either on calculator displays or

indicator panels.

Red LED use as power on indicator

Yellow, green and amber LEDs are also widely available but very

few of you will have seen a blue LED.
http://images.google.com.tr/imgres?imgurl=http://www.logolites.com/images/1948suction.jpg&imgrefurl=http://www.logolites.com/gallery/images.htm&h=294&w=500&sz=21&tbnid=Y9GW4geNy70J:&tbnh=74&tbnw=126&start=91&prev=/images?q=led&start=80&hl=tr&lr=&sa=Nhttp://www.led-watch.com/tx4.htm


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Sample Applications

Street Lighting

Gas Station Lighting

Parking Garage

Parking Lots

Site Lighting

High-baysLow-bays

Wall packs

Decorative Fixtures

Historical Fixtures

Security Lighting


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Security Lighting: Bank drive up


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Street Lighting


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Parking Lot Lights


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Applications

Sensor Applications

Mobile Applications

Sign Applications

Automative Uses

LED Signals

Illuminations

Indicators


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Sensor Applications

Medical Instrumentation

Bar Code Readers

Color & Money Sensors

Encoders

Optical Switches

Fiber Optic Communication
http://www.marktechopto.com/catalog.cfm?Drill_Level=Dept_Series&DeptID=1500


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Mobile Applications

Mobile Phone

PDA's

Digital Cameras

Lap Tops

General Backlighting


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Sign Applications

Full Color Video

Monochrome Message Boards

Traffic/VMS

Transportation - Passenger Information


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Automative Applications

Interior Lighting - Instrument Panels & Switches, Courtesy Lighting

Exterior Lighting - CHMSL, Rear Stop/Turn/Tail

Truck/Bus Lighting - Retrofits, New Turn/Tail/Marker Lights


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Signal Appications

Traffic Rail Aviation Tower Lights

Runway Lights Emergency/Police Vehicle Lighting

LEDs offer enormous benefits over traditional incandescent lampsincluding:

Energy savings (up to 85% less power than incandescent) Reduction in maintenance costs Increased visibility in daylight and adverse weather conditions


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Indication

Household appliances

VCR/ DVD/ Stereo and other audio and video devices

Toys/Games

Instrumentation

Security Equipment

Switches


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Driving LEDs

Analog LED Drive Circuits

Digital LED Drive Circuits


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Colours of LEDs (1/3)

LEDs are available in red, orange, amber, yellow, green, blue andwhite. Blue and white LEDs are much more expensive than the other

colours. The colour of an LED is determined by the semiconductormaterial, not by the colouring of the 'package' (the plastic body). LEDs ofall colours are available in uncoloured packages which may be diffused(milky) or clear (often described as 'water clear'). The coloured packagesare also available as diffused (the standard type) or transparent.

LEDs are made from gallium-basedcrystals that contain one or more additionalmaterials such as phosphorous to produce adistinct color. Different LED chip

technologies emit light in specific regionsof the visible light spectrum and producedifferent intensity levels.


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Tri-colour LEDs

The most popular type of tri-colour LED has a red and a green

LED combined in one package with three leads. They are called tri-colour because mixed red and green light appears to be yellow and thisis produced when both the red and green LEDs are on.

The diagram shows the construction of a tri - colour LED. Notethe different lengths of the three leads. The centre lead (k) is the

common cathode for both LEDs, the outer leads (a1 and a2) are theanodes to the LEDs allowing each one to be lit separately, or bothtogether to give the third colour.


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Bi-colour LEDs

A bi-colour LED has two LEDs wired in'inverse parallel' (one forwards, onebackwards) combined in one package with twoleads. Only one of the LEDs can be lit at onetime and they are less useful than the tri-

colour LEDs described above.


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LED Performance (1/8)

Color White light

Intensity

Eye safety information

Visibility

Operating Life Voltage/Design Current

LED performance is based on a few primary characteristics:


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LED Performance (2/8)

Colour

Peak wavelength is a function of the LED chip material.Although process variations are 10 NM, the 565 to 600 NMwavelength spectral region is where the sensitivity level of thehuman eye is highest. Therefore, it is easier to perceive colorvariations in yellow and amber LEDs than other colors.


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Bargraph 7-segment Starburst Dot matrix

Some Types of LEDs


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Disadvantages:

1.Output power gets affected due to change intemperature

2.Overcurrent damages the LED

3.Large power required for operation

4.Luminous efficiency is low


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::The END::

Thank you for yourAttention!

V.S.ARJUN LED

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