This document provides an overview of LED technology, including its history, types, and benefits. It discusses the development of LEDs from red lights in the 1960s to modern high-brightness blue and white LEDs. Key developments include the invention of high-brightness blue LEDs in the 1990s, which enabled the production of white LEDs through phosphor coating and advanced lighting applications. The document also describes the inner workings of LEDs, comparing their efficiency and lifetime to other light sources, and provides details on connecting, soldering and testing LED circuits.

1. by
B.GOWTHAM PATNAIK
B.PRABHU KIRAN

2. INDEX

3. 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.

4. 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
applications. 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.

5. 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.

6. 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.
h

7. 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

8. 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

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

10. FUNCTIONING,SOLDERING&CONNECTIVITY
Function:
1. LEDs emit light when an electric current passes through
them.
Connecting and soldering:
1. LEDs must be connected the correct way round, the
diagram 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.

11. • 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!

12. BLUE, WHITE & RGB LED'S

15. Thank You
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