a project report on final

8/18/2019 A Project Report on Final

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A PROJECT REPORT ON

ENERGY FROM TRAFFIC

Submitted in partial fulfillment of requirement for the award of degree

Of

BACHELOR OF TECHNOLOGY

In

MECHANICAL ENGINEERING

DR. A.P.J.ABDUL KALAM TECHNICAL UNIVERSITY, LUCKNOW

2015-2016

Guided by: Submitted by:

Mr. ASHU SAXENA RISHU KUMAR (1247640079)

Assistant Professor ROHIT KUMAR (1247640081)

(Department of Mechanical) SUBUHI SHABAB (1347640909)

FIET, Bareilly VISHAL KUMAR (1247640115)

FUTURE INSTITUTE OF ENGINEERING AND TECHNOLOGY

BAREILLY (U.P.)

2015-2016


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FORWARDING LETTER

Forwarded here with is the project report entitled ENERGY FROM

TRAFFIC submitted by RISHU KUMAR, VISHAL KUMAR, ROHIT

KUMAR and SUBUHI SHABAB student of this institution.

The project report is in the partial fulfillment of the requirements towards

the award of the Degree of Bachelor of Technology in Mechanical engineering

[Dr. A.P.J. Abdul Kalam Technology University, Lucknow ].

It has been carried out under the guidance of Mr. Ashu Saxena ( Assistant

Professor ) Department of MECHANICAL ENGINEERING, Future Institute

Of Engineering and Technology, Bareilly.

FORWARDED BY : APPROVED BY:

MR. ASHU SAXENA MR. K.P.S. CHAUHAN

(ASST. PROFESSOR) (H.O.D)

DEPT. OF MECHANICAL ENGG. DEPT. OF MECHANICAL ENGG.

FIET, BAREILLY FIET, BAREILLY


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CERTIFICATE

It is certified that RISHU KUMAR, VISHAL KUMAR, ROHIT KUMAR,

SUBUHI SHABAB student of B-tech (Final year), Department of Mechanical

Engineering has carried out the project work, presented by in this project entitledENERGY FROM TRAFIC for the award of partial fulfillment of the requirement

towards the Bachelor of Technology in Mechanical Engineering from Dr.

A.P.J.ABDUL KALAM TECHNICAL UNIVERSITY LUCKNOW under my

supervision during academic year 2015-16.

Project Guide:- Project Incharge :-

Mr. ASHU SAXENA Mr. Prashant Pratap Mall

Dept.of M.E. Dept. of M.E.

F.I.E.T. BAREILLY F.I.E.T BAREILLY


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Declaration

I hereby declared that submission is own work and to best of my knowledge and

belief .It contain no material previously published or written by another person nor

material which to a substantial extent has been occupied for the award or the any

other degree or diploma of university or other institute of higher learning except

when due acknowledgement has been made in text.

Signature:-

Name:- Rishu Kumar

Roll No:-1247640079

Signature:-

Name:- Vishal Kumar

Roll No:-1247640115

Signature:-

Name: Rohit Kumar

Roll No:-1247640081

Signature:-

Name:- Subuhi Shabab

Roll No:-1347640909


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ACKNOWLEDGEMENT

Many lives & destinies are destroyed due to the lack of proper guidance, directions &

opportunities. It is in this respect I feel that I am in much better condition today due to

continuous process of motivation & focus provided by my parents & teachers in general. The

process of completion of this project was a tedious job & requires care & support at all stages. I

would like to highlight the role played by individuals towards this. I am eternally grateful to

honorable Chairperson Mr. Mukesh Gupta for providing us the opportunity & infrastructure to

complete the project as a partial fulfillment of B.Tech degree in Mechanical engineering.

I am very thankful to MR. K.P.S CHAUHAN Head of Department, for his kind support & faith

in us.

I would like to express my sincere thanks, with deep sense of gratitude to my project guideMR. ASHU SAXENA for their keen interests in my project.

I am also thankful to all visible & invisible hands which helped us to complete this project with a

feeling of success.

THANKING YOU

RISHU KUMAR

VISHAL KUMAR

ROHIT KUMAR

SUBUHI SHABAB


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ABSTRACT

The project here is all about rotation of vehicle are used to converts mechanical energy into

electricity through the use of a roller which are connect with the stepper motor. In this model we

show that how we generate a voltage from the busy road traffic. In all the city traffic is very

much high and on some road, traffic move like a tortoise. If we implant a some speed breaker

type generator on the road then we utilize the friction of vehicle into mechanical energy and

then this mechanical energy is further converted into electrical energy with the help of the

powerful dynamo.


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4.6 PIN 6 – THRESHOLD

4.7 PIN 7 – DISCHARGE

4.8 PIN 8 – V+

5.

LIGHT EMITTING DIODE

5.1 HISTORY

5.2 LED TECHNOLOGY

5.3 COLOURE AND MATERIAL

5.4

TYPES

5.5 CONSIDERATION FOR USE

5.6 LED APPLICATION

6.

ADVANTAGES

7. APPLICATION

8.

CHRISTMAS LIGHT

9.

CONCLUSION

10.

SCOPE FOR FUTURE RESEARCH

11.

REFERENCES


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INTRODUCTION

In this model we show that how we generate a voltage from the busy road traffic. In all the

city traffic is very much high and on some road, traffic move like a tortoise. If we implant a

some speed breaker type generator on the road then we utilize the friction of vehicle into

mechanical energy and then this mechanical energy is further converted into electrical energy

with the help of the powerful dynamo. So we install a one powerful dynamo on the road. Output

of the dyanmo is connected to the l.e.d in this project. When we move the shaft of the dyanmo

then dyanmo generate a voltage and this voltage is sufficient to drive the l.e.d.

In actual practice we use this dyanmo to generate a voltage and after generating a voltage we

charge the battery . When battery is fully charged then we use this battery as a storage device.

We use this storage device to run the lights of the road. In this model we show that how wegenerate a voltage from the busy traffic. conversion of the mechanical energy into electrical

energy is very old concept. We use the same concept in this project. We connect one mechanical

rod with the dynamo and fit this rod on the surface of the road. When any vehicle move from

this roller then due to friction, vehicle Rotate the rod or roller and roller then move the dynamo.

When dynamo move then dynamo generate a voltage and this voltage now connect to the

bulb’s.In actual practice With the help of this voltage we will charge the battery and then we use

this voltage to light then small bulb.

If we install this unit to the any small flyover then with the help of this voltage we generate a

small voltage, and with the help of this voltage we light the bulb.

We use this concept on the very busy road and small generators generate a very small voltage

to the circuit .


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DEFINITION

Stepper motor

The top electromagnet (1) is turned on, attracting the nearest teeth of a gear-shaped iron rotor.

With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet 2.

The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the

nearest teeth slightly to the right. This results in a rotation of 3.6° in this example.

The bottom electromagnet (3) is energized; another 3.6° rotation occurs.

The left electromagnet (4) is enabled, rotating again by 3.6°. When the top electromagnet (1) is

again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25

teeth, it will take 100 steps to make a full rotation in this example.

Because of power requirements, induction of the windings, and temperature management, motors

cannot be powered directly by most digital controllers. Some circuitry that can handle more

power — a motor controller such as an H-bridge — must be inserted between digital controller

and motor's windings. The above image shows the basic circuit of a motor controller that can

also sense motor current. The circuitry to control one winding of a motor is shown; a stepper

motor would use a circuit that could control four windings, and a normal DC motor would need

circuitry to control two windings. All of this circuitry is typically incorporated in an integrated

H-bridge chip.

A stepper motor (or step motor) is a brushless, synchronous electric motor that can divide a

full rotation into a large number of steps. The motor's position can be controlled precisely,

without any feedback mechanism (see open loop control). Stepper motors are similar to switched

reluctance motors (which are very large stepping motors with a reduced pole count, and

generally are closed-loop commutated.)

http://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/Brushless_DC_electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Brushless_DC_electric_motorhttp://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/H-bridge


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winding to rise quickly since dI/dt = V/L where V is very large. The current in each winding is

monitored by the controller, usually by measuring the voltage across a small sense resistor in

series with each winding. When the current exceeds a specified current limit, the voltage is

turned off or "chopped", typically using power transistors. When the winding current drops

below the specified limit, the voltage is turned on again. In this way, the current is held relatively

constant for a particular step position. This requires additional electronics to sense winding

currents, and control the switching, but it allows stepper motors to be driven with higher torque

at higher speeds than L/R drives. Integrated electronics for this purpose are widely available.

Phase current waveforms

A stepper motor is a polyphase AC synchronous motor (see Theory below), and it is ideally

driven by sinusoidal current. A full step waveform is a gross approximation of a sinusoid, and is

the reason why the motor exhibits so much vibration. Various drive techniques have been

developed to better approximate a sinusoidal drive waveform: these are half stepping and

microstepping.

Full step drive (two phases on)

This is the usual method for full step driving the motor. Both phases are always on. The motor

will have full rated torque.

http://en.wikipedia.org/wiki/Electric_motor#Three-phase_AC_synchronous_motorshttp://en.wikipedia.org/wiki/Electric_motor#Three-phase_AC_synchronous_motors


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LITERATURE REVIEW

GENERAL

We use the same concept in this project. We connect one mechanical rod with the dynamo and

fit this rod on the surface of the road. When any vehicle move from this roller then due to

friction, vehicle Rotate the rod or roller and roller then move the dynamo. When dynamo move

then dynamo generate a voltage and this voltage now connect to the bulb’s.In actual practice

With the help of this voltage we will charge the battery and then we use this voltage to light

then small bulb.



ENERGY FROM THE BUSY ROAD

In this model we show that how we generate a voltage from the busy traffic. conversion of the

mechanical energy into electrical energy is very old concept. We use the same concept in this

project. We connect one mechanical rod with the dynamo and fit this rod on the surface of the

road. When any vehicle move from this roller then due to friction, vehicle Rotate the rod or

roller and roller then move the dynamo. When dynamo move then dynamo generate a voltageand this voltage now connect to the bulb’s.In actual practice With the help of this voltage we

will charge the battery and then we use this voltage to light then small bulb.



We use this concept on the very busyroad and small small generators generate a very small

voltage to the circuit


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AUTOMATIC STREET LIGHT USING IC 555.

In this project we show that how we use ic 555 as a automatic street light function. Here in this

project ic 555 work as a monostable timer. Pin no 4 and 8 of the ic is connected to the positive

supply. Pin no 1 of the ic is connected to the ground pin. Pin no 3 is the output pin. On this pin

we connect a output l.e.d. LDR is connected to the pin no 2 of the ic via 100 k ohm resisitor.

When light fall on the ldr then ldr offers a low resistance. When ldr is in dark then ldr offers a

high resistance. When we conver the ldr by hand then ldr resistance become high and so pin no

2 become more more negative. When pin no 2 become negative then ic 555 trigeers itself and

output is on. This is the function of the monostable timer.

IC 555 DETAIL:

The 555 timer IC was first introduced around 1971 by the Signetics Corporation as the

SE555/NE555 and was called "The IC Time Machine" and was also the very first and only

commercial timer ic available. It provided circuit designers and hobby tinkerers with a relatively

cheap, stable, and user-friendly integrated circuit for both monostable and astable applications.


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Since this device was first made commercially available, a myrad of novel and unique circuits

have been developed and presented in several trade, professional, and hobby publications. The

past ten years some manufacturers stopped making these timers because of competition or other

reasons. Yet other companies, like NTE (a subdivision of Philips) picked up where some left off.

Definition of Pin Functions\

Refer to the internal 555 schematic of Fig. 4-2

Pin 1 (Ground): The ground (or common) pin is the most-negative supply potential of the

device, which is normally connected to circuit common (ground) when operated from positive

supplyvoltages.

Pin 2 (Trigger): This pin is the input to the lower comparator and is used to set the latch, which

in turn causes the output to go high. This is the beginning of the timing sequence in monostable

operation. Triggering is accomplished by taking the pin from above to below a voltage level of

1/3 V+ (or, in general, one-half the voltage appearing at pin 5). The action of the trigger input is

level-sensitive, allowing slow rate-of-change waveforms, as well as pulses, to be used as trigger

sources. The trigger pulse must be of shorter duration than the time interval determined by the

external R and C. If this pin is held low longer than that, the output will remain high until the

trigger input is driven high again. One precaution that should be observed with the trigger input

signal is that it must not remain lower than 1/3 V+ for a period of time longer than the timing

cycle. If this is allowed to happen, the timer will re-trigger itself upon termination of the first

output pulse. Thus, when the timer is driven in the monostable mode with input pulses longer

than the desired output pulse width, the input trigger should effectively be shortened by

differentiation. The minimum-allowable pulse width for triggering is somewhat dependent upon

pulse level, but in general if it is greater than the 1uS (micro-Second), triggering will be reliable.

A second precaution with respect to the trigger input concerns storage time in the lower

comparator. This portion of the circuit can exhibit normal turn-off delays of several

microseconds after triggering; that is, the latch can still have a trigger input for this period of

http://www.nteinc.com/http://www.nteinc.com/


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time after the trigger pulse. In practice, this means the minimum monostable output pulse width

should be in the order of 10uS to prevent possible double triggering due to this effect.

Pin 3 (Output): The output of the 555 comes from a high-current totem-pole stage made up

of transistors Q20 - Q24. Transistors Q21 and Q22 provide drive for source-type loads, and their

Darlington connection provides a high-state output voltage about 1.7 volts less than the V+

supply level used. Transistor Q24 provides current-sinking capability for low-state loads referred

to V+ (such as typical TTL inputs). Transistor Q24 has a low saturation voltage, which allows it

to interface directly, with good noise margin, when driving current-sinking logic. Exact output

saturation levels vary markedly with supply voltage, however, for both high and low states. At a

V+ of 5 volts, for instance, the low state Vce(sat) is typically 0.25 volts at 5 mA. Operating at 15

volts, however, it can sink 200mA if an output-low voltage level of 2 volts is allowable (power

dissipation should be considered in such a case, of course). High-state level is typically 3.3 volts

at V+ = 5 volts; 13.3 volts at V+ = 15 volts. Both the rise and fall times of the output waveform

are quite fast, typical switching times being 100nS. The state of the output pin will always reflect

the inverse of the logic state of the latch, and this fact may be seen by examining Fig. 3. Since

the latch itself is not directly accessible, this relationship may be best explained in terms of latch-

input trigger conditions. To trigger the output to a high condition, the trigger input is

momentarily taken from a higher to a lower level. [see "Pin 2 - Trigger"]. This causes the latch to be set and the output to go high. Actuation of the lower comparator is the only manner in which

the output can be placed in the high state. The output can be returned to a low state by causing

the threshold to go from a lower to a higher level [see "Pin 6 - Threshold"], which resets the

latch. The output can also be made to go low by taking the reset to a low state near ground [see

"Pin 4 - Reset"]. The output voltage available at this pin is approximately equal to the Vcc

applied to pin 8 minus 1.7V.

Pin 4 (Reset): This pin is also used to reset the latch and return the output to a low state. The

reset voltage threshold level is 0.7 volt, and a sink current of 0.1mA from this pin is required to

reset the device. These levels are relatively independent of operating V+ level; thus the reset

input is TTL compatible for any supply voltage. The reset input is an overriding function; that is,

it will force the output to a low state regardless of the state of either of the other inputs. It may


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thus be used to terminate an output pulse prematurely, to gate oscillations from "on" to "off", etc.

Delay time from reset to output is typically on the order of 0.5 µS, and the minimum reset pulse

width is 0.5 µS. Neither of these figures is guaranteed, however, and may vary from one

manufacturer to another. In short, the reset pin is used to reset the flip-flop that controls the state

of output pin 3. The pin is activated when a voltage level anywhere between 0 and 0.4 volt is

applied to the pin. The reset pin will force the output to go low no matter what state the other

inputs to the flip-flop are in. When not used, it is recommended that the reset input be tied to V+

to avoid any possibility of false resetting.

Pin 5 (Control Voltage): This pin allows direct access to the 2/3 V+ voltage-divider point,

the reference level for the upper comparator. It also allows indirect access to the lower

comparator, as there is a 2:1 divider (R8 - R9) from this point to the lower-comparator reference

input, Q13. Use of this terminal is the option of the user, but it does allow extreme flexibility by

permitting modification of the timing period, resetting of the comparator, etc. When the 555

timer is used in a voltage-controlled mode, its voltage-controlled operation ranges from about 1

volt less than V+ down to within 2 volts of ground (although this is not guaranteed). Voltages

can be safely applied outside these limits, but they should be confined within the limits of V+

and ground for reliability. By applying a voltage to this pin, it is possible to vary the timing of

the device independently of the RC network. The control voltage may be varied from 45 to 90%

of the Vcc in the monostable mode, making it possible to control the width of the output pulse

independently of RC. When it is used in the astable mode, the control voltage can be varied from

1.7V to the full Vcc. Varying the voltage in the astable mode will produce a frequency

modulated (FM) output. In the event the control-voltage pin is not used, it is recommended that it

be bypassed, to ground, with a capacitor of about 0.01uF (10nF) for immunity to noise, since it is

a comparator input. This fact is not obvious in many 555 circuits since I have seen many circuitswith 'no-pin-5' connected to anything, but this is the proper procedure. The small ceramic cap

may eliminate false triggering.


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Pin 6 (Threshold): Pin 6 is one input to the upper comparator (the other being pin 5) and is

used to reset the latch, which causes the output to go low. Resetting via this terminal is

accomplished by taking the terminal from below to above a voltage level of 2/3 V+ (the normal

voltage on pin 5). The action of the threshold pin is level sensitive, allowing slow rate-of-change

waveforms. The voltage range that can safely be applied to the threshold pin is between V+ and

ground. A dc current, termed the threshold current, must also flow into this terminal from the

external circuit. This current is typically 0.1µA, and will define the upper limit of total resistance

allowable from pin 6 to V+. For either timing configuration operating at V+ = 5 volts, this

resistance is 16 Mega-ohm. For 15 volt operation, the maximum value of resistance is 20

MegaOhms.

Pin 7 (Discharge): This pin is connected to the open collector of a npn transistor (Q14), the

emitter of which goes to ground, so that when the transistor is turned "on", pin 7 is effectively

shorted to ground. Usually the timing capacitor is connected between pin 7 and ground and is

discharged when the transistor turns "on". The conduction state of this transistor is identical in

timing to that of the output stage. It is "on" (low resistance to ground) when the output is low and

"off" (high resistance to ground) when the output is high. In both the monostable and astable

time modes, this transistor switch is used to clamp the appropriate nodes of the timing network to

ground. Saturation voltage is typically below 100mV (milli-Volt) for currents of 5 mA or less,

and off-state leakage is about 20nA (these parameters are not specified by all manufacturers,

however). Maximum collector current is internally limited by design, thereby removing

restrictions on capacitor size due to peak pulse-current discharge. In certain applications, this


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open collector output can

be used as an auxiliary

output terminal,

with current-sinking

capability similar to

the output (pin 3).

Pin 8 (V +): The V+ pin (also referred to as Vcc) is the positive supply voltage terminal of

the 555 timer IC. Supply-voltage operating range for the 555 is +4.5 volts (minimum) to +16

volts (maximum), and it is specified for operation between +5 volts and + 15 volts. The device

will operate essentially the same over this range of voltages without change in timing period.

Actually, the most significant operational difference is the output drive capability, which

increases for both current and voltage range as the supply voltage is increased. Sensitivity of

time interval to supply voltage change is low, typically 0.1% per volt. There are special and

military devices available that operate at voltages as high as 18 V.

Try the simple 555 testing-circuit of Fig. 5. to get you going, and test all your 555 timer ic's. I

build several for friends and family. I bring my own tester to ham-fests and what not to instantly

do a check and see if they are oscillating. Or use as a trouble shooter in 555 based circuits. This

tester will quickly tell you if the timer is functional or not. Although not foolproof, it will tell if

the 555 is shorted or oscillating. If both Led's are flashing the timer is most likely in good

working order. If one or both Led's are either off or on solid the timer is defective. Simple huh?


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Light-emitting diode

"LED" redirects here. For other uses, see LED (disambiguation).

Blue, green, and red LEDs; these can be combined to produce most perceptible colors, including

white. Infrared and ultraviolet (UVA) LEDs are also available.

LED schematic symbol

http://en.wikipedia.org/wiki/LED_(disambiguation)http://en.wikipedia.org/wiki/File:Al_Sheedakim_and_Panel.JPGhttp://en.wikipedia.org/wiki/File:RBG-LED.jpghttp://en.wikipedia.org/wiki/LED_(disambiguation)


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LED displays allow for smaller sets of interchangeable LEDs to be one large display.

A light-emitting-diode (LED) (pronounced /ˌɛliːˈdiː/),[1] is a semiconductor diode that emits

light when an electric current is applied in the forward direction of the device, as in the simple

LED circuit. The effect is a form of electroluminescence where incoherent and narrow-spectrum

light is emitted from the p-n junction in a solid state material.

LEDs are widely used as indicator lights on electronic devices and increasingly in higher power

applications such as flashlights and area lighting. An LED is usually a small area (less than 1

mm2) light source, often with optics added directly on top of the chip to shape its radiation

pattern and assist in reflection.[2][3] The color of the emitted light depends on the composition and

condition of the semiconducting material used, and can be infrared, visible, or ultraviolet.

Besides lighting, interesting applications include using UV-LEDs for sterilization of water and

disinfection of devices,[4] and as a grow light to enhance photosynthesis in plants.[5]

http://en.wikipedia.org/wiki/LED_displayhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/LED#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/LED#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/LED#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Semiconductor_diodehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/LED_circuithttp://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/Coherence_(physics)http://en.wikipedia.org/wiki/Spectrumhttp://en.wikipedia.org/wiki/P-n_junctionhttp://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/LED#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/LED#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/LED#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/UVhttp://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/Grow_lighthttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/LED#cite_note-4#cite_note-4http://en.wikipedia.org/wiki/LED#cite_note-4#cite_note-4http://en.wikipedia.org/wiki/LED#cite_note-4#cite_note-4http://en.wikipedia.org/wiki/LED#cite_note-4#cite_note-4http://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Grow_lighthttp://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/UVhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/LED#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/LED#cite_note-1#cite_note-1http://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/P-n_junctionhttp://en.wikipedia.org/wiki/Spectrumhttp://en.wikipedia.org/wiki/Coherence_(physics)http://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/LED_circuithttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Semiconductor_diodehttp://en.wikipedia.org/wiki/LED#cite_note-0#cite_note-0http://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/LED_display


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Contents

1 History

o

1.1 Discoveries and early deviceso 1.2 Practical use

o 1.3 Continuing development

2 LED technology

o 2.1 Light extraction

o 2.2 Efficiency and operational parameters

o 2.3 Electrical polarity

o 2.4 Failure modes

3 Colors and materials

o 3.1 Ultraviolet and blue LEDs

o 3.2 White light LEDs

3.2.1 RGB Systems

3.2.2 Phosphor based LEDs

o 3.3 Organic light-emitting diodes (OLEDs)

o 3.4 Quantum Dot LEDs (experimental)

4 Types

o 4.1 Miniature LEDs

o 4.2 Flashing LEDs

o 4.3 High power LEDs

o 4.4 Multi-color LEDs

o 4.5 Alphanumeric LED displays

5 Considerations for use

o 5.1 Power sources

o 5.2 Lighting LEDs on mains

o 5.3 Advantages of using LEDs

o 5.4 Disadvantages of using LEDs

6 LED applications

http://en.wikipedia.org/wiki/LED#History#Historyhttp://en.wikipedia.org/wiki/LED#Discoveries_and_early_devices#Discoveries_and_early_deviceshttp://en.wikipedia.org/wiki/LED#Practical_use#Practical_usehttp://en.wikipedia.org/wiki/LED#Continuing_development#Continuing_developmenthttp://en.wikipedia.org/wiki/LED#LED_technology#LED_technologyhttp://en.wikipedia.org/wiki/LED#Light_extraction#Light_extractionhttp://en.wikipedia.org/wiki/LED#Efficiency_and_operational_parameters#Efficiency_and_operational_parametershttp://en.wikipedia.org/wiki/LED#Electrical_polarity#Electrical_polarityhttp://en.wikipedia.org/wiki/LED#Failure_modes#Failure_modeshttp://en.wikipedia.org/wiki/LED#Colors_and_materials#Colors_and_materialshttp://en.wikipedia.org/wiki/LED#Ultraviolet_and_blue_LEDs#Ultraviolet_and_blue_LEDshttp://en.wikipedia.org/wiki/LED#White_light_LEDs#White_light_LEDshttp://en.wikipedia.org/wiki/LED#RGB_Systems#RGB_Systemshttp://en.wikipedia.org/wiki/LED#Phosphor_based_LEDs#Phosphor_based_LEDshttp://en.wikipedia.org/wiki/LED#Organic_light-emitting_diodes_.28OLEDs.29#Organic_light-emitting_diodes_.28OLEDs.29http://en.wikipedia.org/wiki/LED#Quantum_Dot_LEDs_.28experimental.29#Quantum_Dot_LEDs_.28experimental.29http://en.wikipedia.org/wiki/LED#Types#Typeshttp://en.wikipedia.org/wiki/LED#Miniature_LEDs#Miniature_LEDshttp://en.wikipedia.org/wiki/LED#Flashing_LEDs#Flashing_LEDshttp://en.wikipedia.org/wiki/LED#High_power_LEDs#High_power_LEDshttp://en.wikipedia.org/wiki/LED#Multi-color_LEDs#Multi-color_LEDshttp://en.wikipedia.org/wiki/LED#Alphanumeric_LED_displays#Alphanumeric_LED_displayshttp://en.wikipedia.org/wiki/LED#Considerations_for_use#Considerations_for_usehttp://en.wikipedia.org/wiki/LED#Power_sources#Power_sourceshttp://en.wikipedia.org/wiki/LED#Lighting_LEDs_on_mains#Lighting_LEDs_on_mainshttp://en.wikipedia.org/wiki/LED#Advantages_of_using_LEDs#Advantages_of_using_LEDshttp://en.wikipedia.org/wiki/LED#Disadvantages_of_using_LEDs#Disadvantages_of_using_LEDshttp://en.wikipedia.org/wiki/LED#LED_applications#LED_applicationshttp://en.wikipedia.org/wiki/LED#LED_applications#LED_applicationshttp://en.wikipedia.org/wiki/LED#Disadvantages_of_using_LEDs#Disadvantages_of_using_LEDshttp://en.wikipedia.org/wiki/LED#Advantages_of_using_LEDs#Advantages_of_using_LEDshttp://en.wikipedia.org/wiki/LED#Lighting_LEDs_on_mains#Lighting_LEDs_on_mainshttp://en.wikipedia.org/wiki/LED#Power_sources#Power_sourceshttp://en.wikipedia.org/wiki/LED#Considerations_for_use#Considerations_for_usehttp://en.wikipedia.org/wiki/LED#Alphanumeric_LED_displays#Alphanumeric_LED_displayshttp://en.wikipedia.org/wiki/LED#Multi-color_LEDs#Multi-color_LEDshttp://en.wikipedia.org/wiki/LED#High_power_LEDs#High_power_LEDshttp://en.wikipedia.org/wiki/LED#Flashing_LEDs#Flashing_LEDshttp://en.wikipedia.org/wiki/LED#Miniature_LEDs#Miniature_LEDshttp://en.wikipedia.org/wiki/LED#Types#Typeshttp://en.wikipedia.org/wiki/LED#Quantum_Dot_LEDs_.28experimental.29#Quantum_Dot_LEDs_.28experimental.29http://en.wikipedia.org/wiki/LED#Organic_light-emitting_diodes_.28OLEDs.29#Organic_light-emitting_diodes_.28OLEDs.29http://en.wikipedia.org/wiki/LED#Phosphor_based_LEDs#Phosphor_based_LEDshttp://en.wikipedia.org/wiki/LED#RGB_Systems#RGB_Systemshttp://en.wikipedia.org/wiki/LED#White_light_LEDs#White_light_LEDshttp://en.wikipedia.org/wiki/LED#Ultraviolet_and_blue_LEDs#Ultraviolet_and_blue_LEDshttp://en.wikipedia.org/wiki/LED#Colors_and_materials#Colors_and_materialshttp://en.wikipedia.org/wiki/LED#Failure_modes#Failure_modeshttp://en.wikipedia.org/wiki/LED#Electrical_polarity#Electrical_polarityhttp://en.wikipedia.org/wiki/LED#Efficiency_and_operational_parameters#Efficiency_and_operational_parametershttp://en.wikipedia.org/wiki/LED#Light_extraction#Light_extractionhttp://en.wikipedia.org/wiki/LED#LED_technology#LED_technologyhttp://en.wikipedia.org/wiki/LED#Continuing_development#Continuing_developmenthttp://en.wikipedia.org/wiki/LED#Practical_use#Practical_usehttp://en.wikipedia.org/wiki/LED#Discoveries_and_early_devices#Discoveries_and_early_deviceshttp://en.wikipedia.org/wiki/LED#History#History


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o 6.1 Indicators and signs

o 6.2 Lighting

o 6.3 Smart lighting

o 6.4 Non-visual applications

o 6.5 Light sources for machine vision systems

7 Examples of use

o 7.1 Operating Room Surgical LED lights

o 7.2 Christmas lights

8 See also

9 References

10 External links

Discoveries and early devices

The first known report of a light-emitting solid-state diode was made in 1907 by the British

experimenter H. J. Round of Marconi Labs when he noticed electroluminescence produced from

a crystal of silicon carbide while using a cat's-whisker detector .[6] Russian Oleg Vladimirovich

Losev independently created the first LED in the mid 1920s; his research, though distributed in

Russian, German and British scientific journals, was ignored,[7][8] and no practical use was made

of the discovery for several decades. Rubin Braunstein of the Radio Corporation of America

reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in

1955.[9] Braunstein observed infrared emission generated by simple diode structures using GaSb,

GaAs, InP, and Ge-Si alloys at room temperature and at 77 kelvin.

In 1961, experimenters Bob Biard and Gary Pittman working at Texas Instruments,[10] found that

gallium arsenide gave off infrared radiation when electric current was applied. Biard and Pittman

were able to establish the priority of their work and received the patent for the infrared light-

emitting diode.

http://en.wikipedia.org/wiki/LED#Indicators_and_signs#Indicators_and_signshttp://en.wikipedia.org/wiki/LED#Lighting#Lightinghttp://en.wikipedia.org/wiki/LED#Smart_lighting#Smart_lightinghttp://en.wikipedia.org/wiki/LED#Non-visual_applications#Non-visual_applicationshttp://en.wikipedia.org/wiki/LED#Light_sources_for_machine_vision_systems#Light_sources_for_machine_vision_systemshttp://en.wikipedia.org/wiki/LED#Examples_of_use#Examples_of_usehttp://en.wikipedia.org/wiki/LED#Operating_Room_Surgical_LED_lights#Operating_Room_Surgical_LED_lightshttp://en.wikipedia.org/wiki/LED#Christmas_lights#Christmas_lightshttp://en.wikipedia.org/wiki/LED#See_also#See_alsohttp://en.wikipedia.org/wiki/LED#References#Referenceshttp://en.wikipedia.org/wiki/LED#External_links#External_linkshttp://en.wikipedia.org/wiki/H._J._Roundhttp://en.wikipedia.org/wiki/Marconi_Labshttp://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Cat%27s-whisker_detectorhttp://en.wikipedia.org/wiki/LED#cite_note-5#cite_note-5http://en.wikipedia.org/wiki/LED#cite_note-5#cite_note-5http://en.wikipedia.org/wiki/LED#cite_note-5#cite_note-5http://en.wikipedia.org/wiki/Oleg_Vladimirovich_Losevhttp://en.wikipedia.org/wiki/Oleg_Vladimirovich_Losevhttp://en.wikipedia.org/wiki/LED#cite_note-Zheludev_100yearhistory-6#cite_note-Zheludev_100yearhistory-6http://en.wikipedia.org/wiki/LED#cite_note-Zheludev_100yearhistory-6#cite_note-Zheludev_100yearhistory-6http://en.wikipedia.org/wiki/LED#cite_note-Zheludev_100yearhistory-6#cite_note-Zheludev_100yearhistory-6http://en.wikipedia.org/w/index.php?title=Rubin_Braunstein&action=edit&redlink=1http://en.wikipedia.org/wiki/Radio_Corporation_of_Americahttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/LED#cite_note-8#cite_note-8http://en.wikipedia.org/wiki/LED#cite_note-8#cite_note-8http://en.wikipedia.org/wiki/LED#cite_note-8#cite_note-8http://en.wikipedia.org/wiki/Gallium_antimonidehttp://en.wikipedia.org/wiki/GaAshttp://en.wikipedia.org/wiki/Indium_phosphidehttp://en.wikipedia.org/wiki/Texas_Instrumentshttp://en.wikipedia.org/wiki/LED#cite_note-9#cite_note-9http://en.wikipedia.org/wiki/LED#cite_note-9#cite_note-9http://en.wikipedia.org/wiki/LED#cite_note-9#cite_note-9http://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/LED#cite_note-9#cite_note-9http://en.wikipedia.org/wiki/Texas_Instrumentshttp://en.wikipedia.org/wiki/Indium_phosphidehttp://en.wikipedia.org/wiki/GaAshttp://en.wikipedia.org/wiki/Gallium_antimonidehttp://en.wikipedia.org/wiki/LED#cite_note-8#cite_note-8http://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Radio_Corporation_of_Americahttp://en.wikipedia.org/w/index.php?title=Rubin_Braunstein&action=edit&redlink=1http://en.wikipedia.org/wiki/LED#cite_note-Zheludev_100yearhistory-6#cite_note-Zheludev_100yearhistory-6http://en.wikipedia.org/wiki/LED#cite_note-Zheludev_100yearhistory-6#cite_note-Zheludev_100yearhistory-6http://en.wikipedia.org/wiki/Oleg_Vladimirovich_Losevhttp://en.wikipedia.org/wiki/Oleg_Vladimirovich_Losevhttp://en.wikipedia.org/wiki/LED#cite_note-5#cite_note-5http://en.wikipedia.org/wiki/Cat%27s-whisker_detectorhttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/Marconi_Labshttp://en.wikipedia.org/wiki/H._J._Roundhttp://en.wikipedia.org/wiki/LED#External_links#External_linkshttp://en.wikipedia.org/wiki/LED#References#Referenceshttp://en.wikipedia.org/wiki/LED#See_also#See_alsohttp://en.wikipedia.org/wiki/LED#Christmas_lights#Christmas_lightshttp://en.wikipedia.org/wiki/LED#Operating_Room_Surgical_LED_lights#Operating_Room_Surgical_LED_lightshttp://en.wikipedia.org/wiki/LED#Examples_of_use#Examples_of_usehttp://en.wikipedia.org/wiki/LED#Light_sources_for_machine_vision_systems#Light_sources_for_machine_vision_systemshttp://en.wikipedia.org/wiki/LED#Non-visual_applications#Non-visual_applicationshttp://en.wikipedia.org/wiki/LED#Smart_lighting#Smart_lightinghttp://en.wikipedia.org/wiki/LED#Lighting#Lightinghttp://en.wikipedia.org/wiki/LED#Indicators_and_signs#Indicators_and_signs


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The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr.,

while working at General Electric Company. He later moved to the University of Illinois at

Urbana-Champaign.[11] Holonyak is seen as the "father of the light-emitting diode".[12] M.

George Craford, a former graduate student of Holonyak's, invented the first yellow LED and 10x

brighter red and red-orange LEDs in 1972.[13] Up to 1968 visible and infrared LEDs were

extremely costly, on the order of US $200 per unit, and so had little practical application. [14] The

Monsanto Corporation was the first organization to mass-produce visible LEDs, using gallium

arsenide phosphide in 1968 to produce red LEDs suitable for indicators. [15] Hewlett Packard

(HP) introduced light-emitting diodes in 1968, initially using GaAsP material supplied by

Monsanto. The technology proved to have major applications for alphanumeric displays and was

integrated into HP’s early handheld calculators.

Practical use

Some police vehicle lightbars incorporate LEDs.

The first commercial LEDs were commonly used as replacements for incandescent indicators,

and in seven-segment displays, first in expensive equipment such as laboratory and electronics

test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even

watches (see list of signal applications). These red LEDs were bright enough only for use as

indicators, as the light output was not enough to illuminate an area. Later, other colors became

widely available and also appeared in appliances and equipment. As the LED materials

technology became more advanced, the light output was increased, while maintaining the

efficiency and the reliability to an acceptable level. The invention and development of the high

power white light LED led to use for illumination (see list of illumination applications).

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Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with

increasing power output, it has become increasingly necessary to shed excess heat in order to

maintain reliability, so more complex packages have been adapted for efficient heat dissipation.

Packages for state-of-the-art high power LEDs bear little resemblance to early LEDs.

Continuing development

The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation

and was based on InGaN borrowing on critical developments in GaN nucleation on sapphire

substrates and the demonstration of p-type doping of GaN which were developed by Isamu

Akasaki and H. Amano in Nagoya. In 1995, Alberto Barbieri at the Cardiff University

Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs

demonstrated a very impressive result by using a transparent contact made of indium tin oxide

(ITO) on (AlGaInP/GaAs) LED. The existence of blue LEDs and high efficiency LEDs quickly

led to the development of the first white LED, which employed a Y3Al5O12:Ce, or "YAG",

phosphor coating to mix yellow (down-converted) light with blue to produce light that appears

white. Nakamura was awarded the 2006 Millennium Technology Prize for his invention.[16]

The development of LED technology has caused their efficiency and light output to increase

exponentially, with a doubling occurring about every 36 months since the 1960s, in a similarway to Moore's law. The advances are generally attributed to the parallel development of other

semiconductor technologies and advances in optics and material science. This trend is normally

called Haitz's Law after Dr. Roland Haitz.

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[edit] LED technology

Parts of an LED

The inner workings of an LED

I-V diagram for a diode an LED will begin to emit light when the on-voltage is exceeded.

Typical on voltages are 2-3 Volt

Like a normal diode, the LED consists of a chip of semiconducting material impregnated, or

doped , with impurities to create a p-n junction. As in other diodes, current flows easily from the

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p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers —

electrons and holes — flow into the junction from electrodes with different voltages. When an

electron meets a hole, it falls into a lower energy level, and releases energy in the form of a

photon.

The wavelength of the light emitted, and therefore its color, depends on the band gap energy of

the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes

recombine by a non-radiative transition which produces no optical emission, because these are

indirect band gap materials. The materials used for the LED have a direct band gap with energies

corresponding to near-infrared, visible or near-ultraviolet light.

LED development began with infrared and red devices made with gallium arsenide. Advances in

materials science have made possible the production of devices with ever-shorter wavelengths,

producing light in a variety of colors.

LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer

deposited on its surface. P-type substrates, while less common, occur as well. Many commercial

LEDs, especially GaN/InGaN, also use sapphire substrate.

Light extraction

The refractive index of most LED semiconductor materials is quite high, so in almost all cases

the light from the LED is coupled into a much lower-index medium. The large index difference

makes the reflection quite substantial (per the Fresnel coefficients). The produced light gets

partially reflected back into the semiconductor, where it may be absorbed and turned into

additional heat; this is usually one of the dominant causes of LED inefficiency. Often more than

half of the emitted light is reflected back at the LED-package and package-air interfaces.

The reflection is most commonly reduced by using a dome-shaped (half-sphere) package with

the diode in the center so that the outgoing light rays strike the surface perpendicularly, at which

angle the reflection is minimized. Substrates that are transparent to the emitted wavelength, and

backed by a reflective layer, increase the LED efficiency. The refractive index of the package

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material should also match the index of the semiconductor, to minimize back-reflection. An anti-

reflection coating may be added as well.

The package may be colored, but this is only for cosmetic reasons or to improve the contrast

ratio; the color of the packaging does not substantially affect the color of the light emitted.

Other strategies for reducing the impact of the interface reflections include designing the LED to

reabsorb and reemit the reflected light (called photon recycling ) and manipulating the

microscopic structure of the surface to reduce the reflectance, by introducing random roughness,

creating programmed moth eye surface patterns. Recently photonic crystal have also been used to

minimize back-reflections.[17] In December 2007, scientists at Glasgow University claimed to

have found a way to make LEDs more energy efficient, imprinting billions of holes into LEDs

using a process known as nanoimprint lithography.[18]

Efficiency and operational parameters

Typical indicator LEDs are designed to operate with no more than 30 – 60 milliwatts [mW] of

electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous

use at one watt [W]. These LEDs used much larger semiconductor die sizes to handle the large

power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat

removal from the LED die.

One of the key advantages of LED-based lighting is its high efficiency, as measured by its light

output per unit power input. White LEDs quickly matched and overtook the efficiency of

standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a

luminous efficiency of 18 – 22 lumens per watt [lm/W]. For comparison, a conventional 60 – 100

W incandescent lightbulb produces around 15 lm/W, and standard fluorescent lights produce up

to 100 lm/W. (The luminous efficiency article discusses these comparisons in more detail.)

In September 2003, a new type of blue LED was demonstrated by the company Cree, Inc. to

provide 24 mW at 20 milliamperes [mA]. This produced a commercially packaged white light

giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time,

and more than four times as efficient as standard incandescents. In 2006 they demonstrated a

http://en.wikipedia.org/wiki/Anti-reflection_coatinghttp://en.wikipedia.org/wiki/Anti-reflection_coatinghttp://en.wikipedia.org/wiki/Photonic_crystalhttp://en.wikipedia.org/wiki/LED#cite_note-16#cite_note-16http://en.wikipedia.org/wiki/LED#cite_note-16#cite_note-16http://en.wikipedia.org/wiki/LED#cite_note-16#cite_note-16http://en.wikipedia.org/wiki/Glasgow_Universityhttp://en.wikipedia.org/wiki/Nanoimprint_lithographyhttp://en.wikipedia.org/wiki/LED#cite_note-BBC_Rahman-17#cite_note-BBC_Rahman-17http://en.wikipedia.org/wiki/LED#cite_note-BBC_Rahman-17#cite_note-BBC_Rahman-17http://en.wikipedia.org/wiki/LED#cite_note-BBC_Rahman-17#cite_note-BBC_Rahman-17http://en.wikipedia.org/wiki/Milliwatthttp://en.wikipedia.org/wiki/Philips_Lumileds_Lighting_Companyhttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Philips_Lumileds_Lighting_Companyhttp://en.wikipedia.org/wiki/Luminous_efficiencyhttp://en.wikipedia.org/wiki/Lumen_(unit)http://en.wikipedia.org/wiki/Luminous_efficiencyhttp://en.wikipedia.org/wiki/Cree_Inc.http://en.wikipedia.org/wiki/Milliamperehttp://en.wikipedia.org/wiki/Milliamperehttp://en.wikipedia.org/wiki/Cree_Inc.http://en.wikipedia.org/wiki/Luminous_efficiencyhttp://en.wikipedia.org/wiki/Lumen_(unit)http://en.wikipedia.org/wiki/Luminous_efficiencyhttp://en.wikipedia.org/wiki/Philips_Lumileds_Lighting_Companyhttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Philips_Lumileds_Lighting_Companyhttp://en.wikipedia.org/wiki/Milliwatthttp://en.wikipedia.org/wiki/LED#cite_note-BBC_Rahman-17#cite_note-BBC_Rahman-17http://en.wikipedia.org/wiki/Nanoimprint_lithographyhttp://en.wikipedia.org/wiki/Glasgow_Universityhttp://en.wikipedia.org/wiki/LED#cite_note-16#cite_note-16http://en.wikipedia.org/wiki/Photonic_crystalhttp://en.wikipedia.org/wiki/Anti-reflection_coatinghttp://en.wikipedia.org/wiki/Anti-reflection_coating


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prototype with a record white LED luminous efficiency of 131 lm/W at 20 mA. Also, Seoul

Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be

approaching an order of magnitude improvement over standard incandescents and better even

than standard fluorescents.[19] Nichia Corporation has developed a white light LED with

luminous efficiency of 150 lm/W at a forward current of 20 mA.[20]

It should be noted that high- power (≥ 1 W) LEDs are necessary for practical general lighting

applications. Typical operating currents for these devices begin at 350 mA. The highest

efficiency high-power white LED is claimed[21] by Philips Lumileds Lighting Co. with a

luminous efficiency of 115 lm/W (350 mA).

Cree issued a press release on November 19th, 2008 about a laboratory prototype LED achieving

161 lumens/watt at room temperature. The total output was 173 lumens, and the correlated color

temperature was reported to be 4689 K.

Electrical polarity

Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will

only light with correct electrical polarity. When the voltage across the p-n junction is in the

correct direction, a significant current flows and the device is said to be forward-biased . If the

voltage is of the wrong polarity, the device is said to be reverse biased , very little current flows,and no light is emitted. LEDs can be operated on an alternating current voltage, but they will

only light with positive voltage, causing the LED to turn on and off at the frequency of the AC

supply.

Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an

applied reverse voltage above this threshold. LEDs driven directly from an AC supply of more

than the reverse breakdown voltage may be protected by placing a diode (or another LED) in

inverse parallel.

The manufacturer will normally advise how to determine the polarity of the LED in the product

datasheet. However, these methods may also be used:

http://en.wikipedia.org/wiki/Seoul_Semiconductorhttp://en.wikipedia.org/wiki/Seoul_Semiconductorhttp://en.wikipedia.org/wiki/LED#cite_note-18#cite_note-18http://en.wikipedia.org/wiki/LED#cite_note-18#cite_note-18http://en.wikipedia.org/wiki/LED#cite_note-18#cite_note-18http://en.wikipedia.org/wiki/Nichia_Corporationhttp://en.wikipedia.org/wiki/LED#cite_note-19#cite_note-19http://en.wikipedia.org/wiki/LED#cite_note-19#cite_note-19http://en.wikipedia.org/wiki/LED#cite_note-19#cite_note-19http://en.wikipedia.org/wiki/LED#cite_note-20#cite_note-20http://en.wikipedia.org/wiki/LED#cite_note-20#cite_note-20http://en.wikipedia.org/wiki/Incandescent_light_bulbhttp://en.wikipedia.org/wiki/Polarity_(physics)http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Breakdown_voltagehttp://en.wikipedia.org/wiki/Antiparallel_(electronics)http://en.wikipedia.org/wiki/Antiparallel_(electronics)http://en.wikipedia.org/wiki/Breakdown_voltagehttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Polarity_(physics)http://en.wikipedia.org/wiki/Incandescent_light_bulbhttp://en.wikipedia.org/wiki/LED#cite_note-20#cite_note-20http://en.wikipedia.org/wiki/LED#cite_note-19#cite_note-19http://en.wikipedia.org/wiki/Nichia_Corporationhttp://en.wikipedia.org/wiki/LED#cite_note-18#cite_note-18http://en.wikipedia.org/wiki/Seoul_Semiconductorhttp://en.wikipedia.org/wiki/Seoul_Semiconductor


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sign: + -

terminal: anode (A) cathode (K)

leads: long short

exterior: round Flat

interior: small large

wiring: red black

*marking: none stripe

*pin: 1 2

*PCB: round square

*Die placement: connector Cup

(*)Less reliable methods of determining polarity

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Failure modes

The most common way for LEDs (and diode lasers) to fail is the gradual lowering of light output

and loss of efficiency. Sudden failures, however rare, can occur as well. Early red LEDs were

notable for their short lifetime.

Nucleation and growth of dislocations is a known mechanism for degradation of the

active region, where the radiative recombination occurs. This requires a presence of an

existing defect in the crystal and is accelerated by heat, high current density, and emitted

light. Gallium arsenide and aluminium gallium arsenide are more susceptible to this

mechanism than gallium arsenide phosphide and indium phosphide. Due to different

properties of the active regions, gallium nitride and indium gallium nitride are virtually

insensitive to this kind of defect.

Electromigration caused by high current density can move atoms out of the active

regions, leading to emergence of dislocations and point defects, acting as nonradiative

recombination centers and producing heat instead of light.

Ionizing radiation can lead to the creation of defects as well, which leads to issues with

radiation hardening of circuits containing LEDs (e.g., in optoisolators)

Differentiated phosphor degeneration. The different phosphors used in white LEDs

tend to degrade with heat and age, but at different rates causing changes in the produced

light color, for example, purple and pink LEDs often use an organic phosphor

formulation which may degrade after just a few hours of operation causing a major shift

in output color .[23]

Metal diffusion caused by high electrical currents or voltages at elevated temperatures

can move metal atoms from the electrodes into the active region. Some materials, notably

indium tin oxide and silver, are subject to electromigration which causes leakage current

and non radiative recombination along the chip edges. In some cases, especially with

GaN/InGaN diodes, a barrier metal layer is used to hinder the electromigration effects.

http://en.wikipedia.org/wiki/Diode_laserhttp://en.wikipedia.org/wiki/Nucleationhttp://en.wikipedia.org/wiki/Dislocationhttp://en.wikipedia.org/wiki/Dislocationhttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Aluminium_gallium_arsenidehttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Indium_phosphidehttp://en.wikipedia.org/wiki/Gallium_nitridehttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Electromigrationhttp://en.wikipedia.org/wiki/Electromigrationhttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/Radiation_hardeninghttp://en.wikipedia.org/wiki/Optoisolatorhttp://en.wikipedia.org/wiki/LED#cite_note-22#cite_note-22http://en.wikipedia.org/wiki/LED#cite_note-22#cite_note-22http://en.wikipedia.org/wiki/LED#cite_note-22#cite_note-22http://en.wikipedia.org/wiki/Indium_tin_oxidehttp://en.wikipedia.org/wiki/Silverhttp://en.wikipedia.org/wiki/Barrier_metalhttp://en.wikipedia.org/wiki/Barrier_metalhttp://en.wikipedia.org/wiki/Silverhttp://en.wikipedia.org/wiki/Indium_tin_oxidehttp://en.wikipedia.org/wiki/LED#cite_note-22#cite_note-22http://en.wikipedia.org/wiki/Optoisolatorhttp://en.wikipedia.org/wiki/Radiation_hardeninghttp://en.wikipedia.org/wiki/Ionizing_radiationhttp://en.wikipedia.org/wiki/Electromigrationhttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Gallium_nitridehttp://en.wikipedia.org/wiki/Indium_phosphidehttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_arsenidehttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Dislocationhttp://en.wikipedia.org/wiki/Nucleationhttp://en.wikipedia.org/wiki/Diode_laser


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Short circuits Mechanical stresses, high currents, and corrosive environment can lead to

formation of whiskers, causing short circuits.

Thermal runaway Nonhomogenities in the substrate, causing localized loss of thermal

conductivity, can cause thermal runaway where heat causes damage which causes more

heat etc. Most common ones are voids caused by incomplete soldering, or by

electromigration effects and Kirkendall voiding.

Current crowding, non-homogenous distribution of the current density over the

junction. This may lead to creation of localized hot spots, which poses risk of thermal

runaway.

Epoxy degradation Some materials of the plastic package tend to yellow when subjected

to heat, causing partial absorption (and therefore loss of efficiency) of the affected

wavelengths.

Thermal stress Sudden failures are most often caused by thermal stresses. When the

epoxy resin package reaches its glass transition temperature, it starts rapidly expanding,

causing mechanical stresses on the semiconductor and the bonded contact, weakening it

or even tearing it off. Conversely, very low temperatures can cause cracking of the

packaging.

Electrostatic discharge (ESD) may cause immediate failure of the semiconductor

junction, a permanent shift of its parameters, or latent damage causing increased rate of

degradation. LEDs and lasers grown on sapphire substrate are more susceptible to ESD

damage.

Reverse bias Although the LED is based on a diode junction and is nominally a

rectifier, the reverse-breakdown mode for some types can occur at very low voltages and

essentially any excess reverse bias causes immediate degradation, and may lead to vastly

accelerated failure. 5V is a typical, "maximum reverse bias voltage" figure for ordinary

LEDS, some special types may have lower limits.

http://en.wikipedia.org/wiki/Short_circuitshttp://en.wikipedia.org/wiki/Short_circuitshttp://en.wikipedia.org/wiki/Whisker_(metallurgy)http://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Solderinghttp://en.wikipedia.org/wiki/Kirkendall_voidinghttp://en.wikipedia.org/wiki/Current_crowdinghttp://en.wikipedia.org/wiki/Current_crowdinghttp://en.wikipedia.org/wiki/Hot_spothttp://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Thermal_stresshttp://en.wikipedia.org/wiki/Thermal_stresshttp://en.wikipedia.org/wiki/Epoxy_resinhttp://en.wikipedia.org/wiki/Glass_transition_temperaturehttp://en.wikipedia.org/wiki/Wire_bondinghttp://en.wikipedia.org/wiki/Electrostatic_dischargehttp://en.wikipedia.org/wiki/Electrostatic_dischargehttp://en.wikipedia.org/wiki/Sapphirehttp://en.wikipedia.org/wiki/Reverse_biashttp://en.wikipedia.org/wiki/Reverse_biashttp://en.wikipedia.org/wiki/Reverse_biashttp://en.wikipedia.org/wiki/Sapphirehttp://en.wikipedia.org/wiki/Electrostatic_dischargehttp://en.wikipedia.org/wiki/Wire_bondinghttp://en.wikipedia.org/wiki/Glass_transition_temperaturehttp://en.wikipedia.org/wiki/Epoxy_resinhttp://en.wikipedia.org/wiki/Thermal_stresshttp://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Hot_spothttp://en.wikipedia.org/wiki/Current_crowdinghttp://en.wikipedia.org/wiki/Kirkendall_voidinghttp://en.wikipedia.org/wiki/Solderinghttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_runawayhttp://en.wikipedia.org/wiki/Whisker_(metallurgy)http://en.wikipedia.org/wiki/Short_circuits


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Colors and materials

Conventional LEDs are made from a variety of inorganic semiconductor materials, the following

table shows the available colors with wavelength range, voltage drop and material:

ColorWavelength

[nm]Voltage [V] Semi-conductor Material

Infrared λ > 760 ΔV < 1.9Gallium arsenide (GaAs)

Aluminium gallium arsenide (AlGaAs)

Red 610 < λ < 760 1.63 < ΔV <

2.03

Aluminium gallium arsenide (AlGaAs)

Gallium arsenide phosphide (GaAsP)

Aluminium gallium indium phosphide (AlGaInP)

Gallium(III) phosphide (GaP)

Orange 590 < λ < 610 2.03 < ΔV <2.10




Yellow 570 < λ < 5902.10 < ΔV <

2.18




Green 500 < λ < 570 2.18 < ΔV <

4.0

Indium gallium nitride (InGaN) / Gallium(III)

nitride (GaN)



http://en.wikipedia.org/wiki/Semiconductor_materialshttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Delta_(letter)http://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Aluminium_gallium_arsenidehttp://en.wikipedia.org/wiki/Redhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Aluminium_gallium_arsenidehttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Orange_(colour)http://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Yellowhttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Gallium(III)_nitridehttp://en.wikipedia.org/wiki/Gallium(III)_nitridehttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Gallium(III)_nitridehttp://en.wikipedia.org/wiki/Gallium(III)_nitridehttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Yellowhttp://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Orange_(colour)http://en.wikipedia.org/wiki/Gallium(III)_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_indium_phosphidehttp://en.wikipedia.org/wiki/Gallium_arsenide_phosphidehttp://en.wikipedia.org/wiki/Aluminium_gallium_arsenidehttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Redhttp://en.wikipedia.org/wiki/Aluminium_gallium_arsenidehttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Delta_(letter)http://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Semiconductor_materials


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Aluminium gallium phosphide (AlGaP)

Blue 450 < λ < 500 2.48 < ΔV <

3.7

Zinc selenide (ZnSe)

Indium gallium nitride (InGaN)

Silicon carbide (SiC) as substrate

Silicon (Si) as substrate — (under development)

Purple multiple types2.48 < ΔV <

3.7

Dual blue/red LEDs,

blue with red phosphor,

or white with purple plastic

Violet 400 < λ < 450 2.76 < ΔV <

4.0Indium gallium nitride (InGaN)

Ultraviolet λ < 400

3.1 < ΔV <

4.4

diamond (C)

Aluminium nitride (AlN)

Aluminium gallium nitride (AlGaN)Aluminium gallium indium nitride (AlGaInN) —

(down to 210 nm[24])

White Broad spectrum ΔV = 3.5 Blue/UV diode with yellow phosphor

http://en.wikipedia.org/wiki/Aluminium_gallium_phosphidehttp://en.wikipedia.org/wiki/Bluehttp://en.wikipedia.org/wiki/Zinc_selenidehttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Purplehttp://en.wikipedia.org/wiki/Violet_(color)http://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Diamondhttp://en.wikipedia.org/wiki/Aluminium_nitridehttp://en.wikipedia.org/wiki/Aluminium_gallium_nitridehttp://en.wikipedia.org/w/index.php?title=Aluminium_gallium_indium_nitride&action=edit&redlink=1http://en.wikipedia.org/wiki/LED#cite_note-23#cite_note-23http://en.wikipedia.org/wiki/LED#cite_note-23#cite_note-23http://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/LED#cite_note-23#cite_note-23http://en.wikipedia.org/w/index.php?title=Aluminium_gallium_indium_nitride&action=edit&redlink=1http://en.wikipedia.org/wiki/Aluminium_gallium_nitridehttp://en.wikipedia.org/wiki/Aluminium_nitridehttp://en.wikipedia.org/wiki/Diamondhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Violet_(color)http://en.wikipedia.org/wiki/Purplehttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Indium_gallium_nitridehttp://en.wikipedia.org/wiki/Zinc_selenidehttp://en.wikipedia.org/wiki/Bluehttp://en.wikipedia.org/wiki/Aluminium_gallium_phosphide


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Ultraviolet and blue LEDs

Blue LEDs.

Blue LEDs are based on the wide band gap semiconductors GaN (gallium nitride) and InGaN

(indium gallium nitride). They can be added to existing red and green LEDs to produce the

impression of white light, though white LEDs today rarely use this principle.

The first blue LEDs were made in 1971 by Jacques Pankove (inventor of the gallium nitride

LED) at RCA Laboratories.[25] However, these devices had too little light output to be of much

practical use. In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping by

Isamu Akasaki and Hiroshi Amano (Nagoya, Japan)[26] ushered in the modern era of GaN-based

optoelectronic devices. Building upon this foundation, in 1993 high brightness blue LEDs were

demonstrated through the work of Shuji Nakamura at Nichia Corporation.[27]

By the late 1990s, blue LEDs had become widely available. They have an active region

consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN,

called cladding layers. By varying the relative InN-GaN fraction in the InGaN quantum wells,

the light emission can be varied from violet to amber. AlGaN aluminium gallium nitride ofvarying AlN fraction can be used to manufacture the cladding and quantum well layers for

ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological

maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, as

opposed to alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths

http://en.wikipedia.org/wiki/Bluehttp://en.wikipedia.org/wiki/Band_gaphttp://en.wikipedia.org/wiki/Gallium_nitridehttp://en.wikipedia.org/wiki/InGaNhttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/RCAhttp://en.wikipedia.org/wiki/LED#cite_note-24#cite_note-24http://en.wikipedia.org/wiki/LED#cite_note-24#cite_note-24http://en.wikipedia.org/wiki/LED#cite_note-24#cite_note-24http://en.wikipedia.org/wiki/Epitaxialhttp://en.wikipedia.org/wiki/P-typehttp://en.wikipedia.org/wiki/Isamu_Akasakihttp://en.wikipedia.org/wiki/LED#cite_note-25#cite_note-25http://en.wikipedia.org/wiki/LED#cite_note-25#cite_note-25http://en.wikipedia.org/wiki/LED#cite_note-25#cite_note-25http://en.wikipedia.org/wiki/Shuji_Nakamurahttp://en.wikipedia.org/wiki/Nichia_Corporationhttp://en.wikipedia.org/wiki/LED#cite_note-26#cite_note-26http://en.wikipedia.org/wiki/LED#cite_note-26#cite_note-26http://en.wikipedia.org/wiki/LED#cite_note-26#cite_note-26http://en.wikipedia.org/wiki/Quantum_wellhttp://en.wikipedia.org/wiki/Aluminium_gallium_nitridehttp://en.wikipedia.org/wiki/File:Blue_LED_and_Reflection.JPGhttp://en.wikipedia.org/wiki/Aluminium_gallium_nitridehttp://en.wikipedia.org/wiki/Quantum_wellhttp://en.wikipedia.org/wiki/LED#cite_note-26#cite_note-26http://en.wikipedia.org/wiki/Nichia_Corporationhttp://en.wikipedia.org/wiki/Shuji_Nakamurahttp://en.wikipedia.org/wiki/LED#cite_note-25#cite_note-25http://en.wikipedia.org/wiki/Isamu_Akasakihttp://en.wikipedia.org/wiki/P-typehttp://en.wikipedia.org/wiki/Epitaxialhttp://en.wikipedia.org/wiki/LED#cite_note-24#cite_note-24http://en.wikipedia.org/wiki/RCAhttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/InGaNhttp://en.wikipedia.org/wiki/Gallium_nitridehttp://en.wikipedia.org/wiki/Band_gaphttp://en.wikipedia.org/wiki/Blue


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around 350 – 370 nm. Green LEDs manufactured from the InGaN-GaN system are far more

efficient and brighter than green LEDs produced with non-nitride material systems.

With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths

are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the

market. Near-UV emitters at wavelengths around 375 – 395 nm are already cheap and often

encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting

UV watermarks in some documents and paper currencies. Shorter wavelength diodes, while

substantially more expensive, are commercially available for wavelengths down to 247 nm.[28]

As the photosensitivity of microorganisms approximately matches the absorption spectrum of

DNA, with a peak at about 260 nm, UV LEDs emitting at 250 – 270 nm are to be expected in

prospective disinfection and sterilization devices. Recent research has shown that commerciallyavailable UVA LEDs (365 nm) are already effective disinfection and sterilization devices.[4]

Wavelengths down to 210 nm were obtained in laboratories using aluminium nitride.

While not an LED as such, an ordinary NPN bipolar transistor will emit violet light if its emitter-

base junction is subjected to non-destructive reverse breakdown. This is easy to demonstrate by

filing the top off a metal-can transistor (BC107, 2N2222 or similar) and biasing it well above

emitter-base breakdown (≥ 20 V) via a current-limiting resistor.

White light LEDs

There are two ways of producing high intensity white-light using LEDs. One is to use individual

LEDs that emit three primary colors[29] – red, green, and blue, and then mix all the colors to

produce white light. The other is to use a phosphor material to convert monochromatic light from

a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb

works.

RGB Systems

Combined spectral curves for blue, yellow-green, and high brightness red solid-state

semiconductor LEDs. FWHM spectral bandwidth is approximately 24 – 27 nm for all three colors.

http://en.wikipedia.org/wiki/Aluminum_gallium_nitridehttp://en.wikipedia.org/w/index.php?title=Aluminum_gallium_indium_nitride&action=edit&redlink=1http://en.wikipedia.org/wiki/Black_lighthttp://en.wikipedia.org/wiki/Counterfeitinghttp://en.wikipedia.org/wiki/LED#cite_note-27#cite_note-27http://en.wikipedia.org/wiki/LED#cite_note-27#cite_note-27http://en.wikipedia.org/wiki/LED#cite_note-27#cite_note-27http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/Aluminium_nitridehttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/Primary_colorhttp://en.wikipedia.org/wiki/Primary_colorhttp://en.wikipedia.org/wiki/Primary_colorhttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/Full_width_at_half_maximumhttp://en.wikipedia.org/wiki/Full_width_at_half_maximumhttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/Primary_colorhttp://en.wikipedia.org/wiki/Primary_colorhttp://en.wikipedia.org/wiki/Whitehttp://en.wikipedia.org/wiki/Aluminium_nitridehttp://en.wikipedia.org/wiki/LED#cite_note-water_sterilization-3#cite_note-water_sterilization-3http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/LED#cite_note-27#cite_note-27http://en.wikipedia.org/wiki/Counterfeitinghttp://en.wikipedia.org/wiki/Black_lighthttp://en.wikipedia.org/w/index.php?title=Aluminum_gallium_indium_nitride&action=edit&redlink=1http://en.wikipedia.org/wiki/Aluminum_gallium_nitride


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White light can be produced by mixing differently colored light, the most common method is to

use red, green and blue (RGB). Hence the method is called multi-colored white LEDs

(sometimes referred to as RGB LEDs). Because its mechanism is involved with sophisticated

electro-optical design to control the blending and diffusion of different colors, this approach has

rarely been used to mass produce white LEDs in the industry. Nevertheless this method is

particularly interesting to many researchers and scientists because of the flexibility of mixing

different colors.[30] In principle, this mechanism also has higher quantum efficiency in producing

white light.

There are several types of multi-colored white LEDs: di-, tri-, and tetrachromatic white LEDs.

Several key factors that play among these different approaches

a project report on final

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