byB.GOWTHAM PATNAIK

B.PRABHU KIRAN

INDEX

INTRODUCTION

• Billions of visible LEDs are produced each year.• it area is of 2mm2

• The emergence of high brightness AlGaAs and AlInGaP devices has given rise to many new markets.

• LED technology has been spurred by the introduction of AlInGaP devices.

• Recently developed AlGaInN materials have led to the improvements in the performance of bluish-green LEDs, which have luminous efficacy peaks much higher than those for incandescent lamps.

• This advancement has led to the production of large-area full-color outdoors LED displays with diverse industrial applications.

HISTORY

• In 1962, when Nick Holonyak Jr. invented first visible led, emitting red light but they are not enough to illuminate surroundings.

• hence used as indicators,seven segment displays like(calculators,watches,tv,telephones etc..)

• By mid 1970’s,more colours green, yellow were manufactured • it got somewhat succeeded with improved efficiency.• In early 1980’s LED were being used for messages and other outdoor appli

cations. They used less power and were ten times brighter than previous ones.

• By early 1990’s High brightness LED packages were developed and were widespread used in Traffic lights.

contd.

• A remarkable milestone was achieved in mid 1990’s when Dr.Shuji Nakamura of Nichia chemical Corporation invented high brightness GaN blue LED. It was this LED that paved path for the development of white LED when coated with phosphor. By this technique white LED’s were produced by 1993.

• This was the pre phase of the giant leap of LEDs, which made it possible to use them for illumination by invention and development of high power white light LEDs.

• Today LEDs have reached performance levels far exceeding previous projections. Market expectations have increased and a wide range of applications including facade lighting, general purpose illumination.

INSIDE THE LED LIGHTINGS

• The way these tiny blinkers light up is far different from the traditional counterparts

• When a PN junction diode is forward biased, the electrons and holes move in opposite directions.

• During this free movement,an electron may fall into hole releasing some energy.

• This energy is in the form photon and hence light is emitted.

• This phenomenon is termed as Electroluminescence.

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LIGHT SOURCE COMPARISION

LIGHT TYPE LIFE TIME

Incandescent 3k

Halogen 10k

T12 fluorescent 20k

Metal halide 5k-15k

T8 fluorescent 20k

Best-in-Class Power LED >60k

High-pressure sodium 20-24k

T5 fluorescent 20k

Low-pressure sodium 18k

LED TYPES

• LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as the actual color of light emitted.

• purple plastic is often used for infrared LEDs.• most blue devices have colourless housings.• Modern high power LEDs such as those used for lighting and backlighting

are generally found in surface-mount technology

LED BENIFITS

Efficiency: LEDs emit more light than incandescent light bulbs. The Efficiency of LED lighting is not affected by shape and size, unlike fl

uorescent light bulbs or tubes.Color: LEDs can emit light of an intended color without using any color filters

as traditional lighting methods need. This is more efficient and can lower initial costs.

Size: LEDs can be very small (smaller than 2mm2 and are easily attached to printed circuit boards.

On/Off time: LEDs light up very quickly. LEDs used in communications devices can have even faster response times.

Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike fluorescent lamps that fail faster when cycled often.

Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.Lifetime: LEDs can have a relatively long useful life.

FUNCTIONING,SOLDERING&CONNECTIVITY

Function:1. LEDs emit light when an electric current passes through th

em.Connecting and soldering:1. LEDs must be connected the correct way round, the diagra

m may be labelled a or + for anode and k or - for cathode.The cathode is the short lead and there may be a slight flat on the body of round LEDs. If you can see inside the LED the cathode is the larger electrode (but this is not an official identification method).

2. LEDs can be damaged by heat when soldering, but the risk is small unless you are very slow. No special precautions are needed for soldering most LEDs.

• Testing an LED

• Never connect an LED directly to a battery or power supply! • It will be destroyed almost instantly because too much current will pass through and burn it out.• LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k

resistor is suitable for most LEDs if your supply voltage is 12V or less. Remember to connect the LED the correct way round!

BLUE, WHITE & RGB LED'S

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