solid state lighting hard copy

8/7/2019 solid state lighting hard copy

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SOLID STATE LIGHTING

TABLE OF CONTENTS:

Abstract

History

Introduction

Definition:

LED Mechanism

Types of LEDs

Available colors in LEDs

Manufacturing the White LEDs

LED Fabrication process

Lowering the operating temperature

Reduction of heat emission

Advantages

Limiting Factors

Applications

Conclusion

Bibliography



Abstract:

Just as transistors replaced vacuum tubes 50 years ago, and just as flat panel

displays are now replacing CRT monitors and televisions, solid state lighting will likely

take the place of incandescent and fluorescent lamps used for applications in general

illumination.

High power Light emitting diodes (LEDs) have begun to differentiate themselves

from their more common cousins the indicator LED. Today these LEDs are designed to

generate 10-100 lm per LED with efficiencies that surpass incandescent and halogen

bulbs. The term "solid state" refers commonly to light emitted by sol

electroluminescence, as opposed to incandescent bulbs (which use thermal radiation) or

fluorescent tubes. Compared to incandescent lighting, SSL creates visible light with

reduced heat generation or parasitic energy dissipation. Most common "white" LEDs

convert blue light from a solid-state device to an (approximate) white light spectrum

using photoluminescence, the same principle used in conventional fluorescent tubes.

Lighting uses 19 % of worldwide electrical energy; this could be reduced by 75 % if all

existing lighting were replaced by solid state lighting. SSL has been identified not only to

fill the efficiency gap but also to replace environmentally unfriendly com

fluorescence lamps and the associated problem of Mercury disposal. The LED is a

basically a small area source, often with extra optics added to the chip that shapes its

radiation pattern. The specific wavelength or color emitted by the LED depends on the

materials used to make the diode. It depends on the composition and condition of the

semi conducting of material used, and can be infrared, visible or near ultraviolet. We

demonstrate record performance and reliability for high power colored LEDs and showresults from the worlds first 100-plus lumen white LED lamp, the solid state equivalent

of Thomas Edison’s 20-W incandescent light bulb approximately one century later.

Solid-state lighting (SSL) refers to a type of lighting that uses semiconductor light-

emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting

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diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in

arc lamps such as fluorescent lamps), or gas.

History:

Oil lamp Incandescent bulbs Fluorescence &

discharge

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

the British experimenter H. J. Round. However, no practical use was made of the

discovery for several decades. Independently, Oleg Vladimirovich Losev published

"Luminous carborundum [silicon carbide] detector and detection with crystals" in the

Russian journal Telegrafiya Telefoniya bez Provodov (Wireless Telegraphy

Telephony). Losev's work languished for decades.

The first practical LED was invented by Nick Holonyak, Jr., in 1962 while he was

at General Electric Company. The first LEDs became commercially available in late

1960s, and were red. They were commonly used as replacements for incandescent

indicators, and in seven-segment displays, first in expensive equipment such

laboratory and electronics test equipment, then later in such appliances as TVs, radios,telephones, calculators, and even watches. 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, and

LEDs became bright enough to be used for illumination.

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Most LEDs were made in the very common 5 mm T1-3/4 and 3 mm T1 packages,

but with higher power, it has become increasingly necessary to get rid of the heat, so the

packages have become more complex and adapted for heat dissipation. Packages for

state-of-the-art high power LEDs bear little resemblance to early LEDs (see, for example,

Philips Lumileds).

Introduction:

LIGHT EMITTING DIODES (LEDs) have gained broad recognition as the

ubiquitous little lights that tell us our monitors are on, the phone is off the hook or the

oven is hot. Recent advances in AlInGaP (Aluminium, Indium, Gallium, Phosphate) Red

and AlInGaN (Aluminium, Indium, Gallium, Nitride) Blue and Green semiconductor

growth technology have enabled applications wherein several single to several millions

of these indicator style LEDs can be packaged together to be used in full color signs,

automotive interior and exterior signaling applications including traffic signals.

Definition:

Light Emitting Diode (LED) is essentially a PN junction semiconductor diode that

emits a monochromatic (single color) light when operated in a forward biased direction.

The basic structure of an LED consists of the die or light emitting semiconductor

material, a lead frame where the die is actually placed, and the encapsulation epoxy

which surrounds and protects the die

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LED Mechanism:

• n-type & p-type semiconductors are combined in one device.

• With the application of a voltage between the p-side and the n-side, free electrons

from the n-type side go to the p-type side through the junction.

• When an electron meets a hole, it recombines and thus releases its energy by

emitting a photon.

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Types of LEDs:

Organic LED & Polymer LED

These are LEDs whose emissive electroluminescent layer is composed of an

organic compound or polymer that will luminescence blue, green and red, and are

covered with a translucent material.

Available colors in LEDs:

1. Infrared

2. Red

3. Orange

4. Yellow5. Green

6. Blue

7. Violet

8. Purple

9. Ultraviolet

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10. White

Manufacturing the White LEDs:

• 1st technique: Found in 1993, when the first blue LED was produced.

• By juxtaposing at a certain distance blue, red, and green LEDs, white light was

obtained.

• 2nd technique: found in 1996 by Nichia Corp. and Fraunhofer Institute

• Start with LED with an active layer made of InGaN

• Cover this structure is covered with a yellow phosphor crystal coating

(Ce3+:YAG).

The LED chip emits blue light, which is converted to yellow light by the phosphor

Other techniques of creating white LEDs:

• Coat near ultra-violet (NUV) with europium-based red and blue emit

phosphors

• Transfer NUV radiation to visible light via the photoluminescence process in

phosphor materials

• Method less efficient then with the blue LED because of photodegradation of the

epoxy resin used in LED packaging.

• Coat blue LEDs with quantum dots, which absorb the blue light and emit a warm

white light.

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LED Fabrication process:

• Electrical contacts to the p- and n-layers are both on the top surface of the

device because of the insulating sapphire substrate.

• The area of the contact to the p-layer has to be maximized to promote current

spreading

• Maximizes light emission and minimizes turn-on voltage and series resistance

• Because most of the light generated at the junction escapes the device through

the top surface

• The large-area p-contact has to be made as transparent as possible outside the

area where electrical bond wires are attached.

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Lowering the operating temperature:

Normal LED:

• Big thermal resistance in thermal conduction path

• Large amount of heat transferred from active layer through front face of LED and

the encapsulating material and then dissipated into the air

Flip Chip LED:

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Designed with a thermal conductive sub mount and metal interconnections to conduct

most of the heat through sub mount.

Reduction of heat emission:

• Some LED lamps are designed with series resistors to limit the operating

current, resulting in no cold filament current variation.

• Room temperature stays cooler, so we don’t need further air conditioning

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Advantages:

1. Lifetime: AS a solid state light source LEDs have a long life time and are

generally very robust due to no mechanical or moving parts. LEDs can last

up to 50,000 hours – more than 5 years of continuous use.

2. Low maintenance: The long life time of LEDs reduces the need to replace

failed lamps and this can lead to significant financial and environmental

savings, particularly in maintenance, labor and recycling.

3. Low power consumption: The low power consumption of LEDs leads tolarge energy savings.

4. Efficiency: As a semiconductor device, LEDs are highly efficient. The

directional nature of light produced by LEDs allow the design of luminaries

with higher over all efficiency.

5. Brightness: Light outputs of LEDs are constantly being increased and there

are several products that have higher lumen output than traditional lighting

6. Heat: Almost 80% of the energy consumed by LEDs is converted in to light

and only some of it is dissipated as heat

7. Instantaneous switch on: LEDs switch on rapidly, even when cold and this

is particular advantage for certain applications such as Vehicle brake lights.

These light up very quickly and achieve full brightness within a few

microseconds.

8. Color: LEDs are available in a broad range of brilliant, saturated colors.

White devices are also available.

9. Small form factor: LEDs are very small. Typically, high brightness LEDs

chips measure 0.3x0.3 mm2, whole high power devices can be 1x1 mm2 or

larger.

10. Environment friendly:

- Less CO2 emission

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- Less light pollution

- Positive impact on Global warming.

Limiting Factors:

Cost Competitiveness

• Now, LED prices are 10 times higher than of incandescent light bulbs

Narrow angle of emission

• To use LEDs in ambient lighting, multiple LEDs are asembled in a single fixture.

This leads to sharp shadows.

High quality variation

• Inexpensive LEDs have inconsistent color temperature and light output

Poor Quantum efficiency

• LEDs are currently limited by poor internal quantum and light-extrac

efficiency, but photonic crystals offer a potential solution to both problems.

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Applications:

1. Traffic Signals: Railroad crossing signals

2. Buildings: LEDs can be used as decorative lights on buildings

3. Digital clock : LEDs are used to indicate the alphanumeric displays in digital clock

4. Residential: For home lighting

5. Information Boards: LEDs are used to indicate the information by alphanumeric

displays

6. Runway in Airports: Lighting on the runway by LEDs

7. Brake lights: Because of their long life and fast switching times, LEDs have been used

for automotive high-mounted brake lights and truck and bus brake lights

8. Battery level Indicator: Red or yellow LEDs are used in indicator and alphanumeric

displays in environments where night vision must be retained: aircraft cockpits,

submarine and ship bridges, astronomy observatories, and in the field, e.g. night time

animal watching and military field use.

9. Street Lights: Instead of toxic mercury’s as street light, LEDs are ultimate form of

light from all point of view.

10. Backlighting for LCD televisions and displays: The availability of LEDs in specific

colors (RGB) enables a full-spectrum light source which expands the color gamut by

as much as45%..

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Conclusion:

We conclude that LED is an ultimate form of lamp, in principle and practice and

its development are realized indeed can & will continue until all powers & colors are

realized. White LEDs for home lighting offer great benefits for the far flung tribal

villages of India.Whether it be a climate change caused by global warming or huge electricity bills

of your house, LED lights are the answer to all the worries. Already being used, we

assure these are definitely going to replace the lamps that we use today in future.

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Bibliography

Websites :

http://lighting.sandia.gov

http://www.loe.org

http://www.enn.com

http://www.netl.doe.gov

http://www.nichia.com

http://cree.com

www.lumileds.com

Books:

Introduction to Solid state lighting by A. Zukauskas, M.S.Shur,R.Gaska

LEDs progress in Solid state lighting by A. Zukauskas, M.S.Shur,R.Gaska

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http://lighting.sandia.gov/


http://www.loe.org/

http://www.loe.org/

http://www.enn.com/

http://www.enn.com/

http://www.netl.doe.gov/


http://www.nichia.com/


http://cree.com/

http://cree.com/

http://www.lumileds.com/



http://www.loe.org/

http://www.enn.com/



http://cree.com/




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