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WELCOMETOLIME LITE

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Efficacy

(relative)

15th 19th 20th century...

1 10 15 70 100 70 100 Target >50

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What Is A Light Emitting Diode

BASIC LED IS A FORWARD-BIASED P/N JUNCTION

The basic starting material is a substrate. On this, a very thin layer (called the epilayer)is formed by a process known as EPITAXY.

Electrons and holes are injected into the P- and N- semiconductor materialsrespectively

Injected minority charges recombine with majority charges in the depletion zone

With certain semiconductor compounds (from III and V in the Periodic Table), thisrecombination results in photon generation of of a specific frequency (colour)

Close-up view of a light

emitting diode in a T-1(5mm) radial package. Theemissive semiconductor isthe small rectangle in thecenter, attached to electricalleads and encased in a lens.

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Diagram of an LED in a T-1 (5mm) radial package

Internal Construction of an LED

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Opto-electrical properties of LEDs(1)

DRIVE CONDITIONS: Similar to other silicon or germanium diodes;

similar electrical parameters such as:

TEMPERATURE DEPENDENCE-- All parameters are measured at 25C

-- DERATING FACTOR AT HIGHER TEMPERATURE-- Heat generated at P and N ohmic contacts, but max. at P-N

junction (Tj). Dissipation only by conducting leads -- path of least

resistance. Excessive heat (more than 130C for AlInGaP) results inshorter life, faster light degradation, and change in VFand IV.

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Opto-electrical properties of LEDs(2)

Viewing Angle (2)

Double the angle of the limit where intensity decreases to halfthe axial value

Narrow angle 60.

Peak Wavelength wavelength of maximum intensity

Dominant Wavelength represents hue as per CIE chromaticityDiagram (important by white)

Chromaticity co-ordinates (for white): X & Y co-ordinates onchromaticity diagram

Colour Temperature: Equivalent colour of black body at thattemperature in degrees Kelvin

Warm white -- 2700 - 3000K; Daylight 6500K

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Opto-electrical properties of LEDs (3)

Colour Rendering Index (CRI)

Colour rendering of objects with particular light Preferred -- more than 90% Lately considered unsuitable indicator

LIFE (hours) Catastrophic failure unusual, and therefore MTBF very high (in millions

of hours) Useful Life considered at limit when light depreciates to 50% of initial Life affected by

Ambient temperature Electrical current surges Chemical reaction with epoxy encapsulant UV radiation (solar UVA and UVB)

Humidity and moisture

Useful life stated up to 100,000 hours till last decade now mayexceed 250,000 hours

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LED Control Circuits(1)

DESIGN CONSIDERATIONS

Design current should be 50%-60% of max. forward current forthe type of LED being used

Derating factor with temperature should be taken into account

Current change with voltage fluctuation (as in battery chargesupply) should be kept within a safe limit

Circuit enclosure should be designed to dissipate the heat soas to prevent temperature rise of LEDs

PIV protection to be provided

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LED Control Circuits(2)

CIRCUITS

1. RESISTIVE CIRCUIT (AC/DC):Resistance drops the voltage andcurrent to the desired value

R

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LED Control Circuits(3)

CIRCUITS

2. REACTIVE IMPEDANCE CIRCUIT (AC ONLY):Using capacitiveimpedance with a fixed frequency

-- Current control with least power consumption-- Minimal heat dissipation-- Improved leading power factor

PRECAUTIONARY MEASURES Initial charging current may damage LED Fuse for protection of external equipment Low voltage glow protection in certain applications Surge/spike transient protection by MOVs, etc

LVGPMOV

c

FUSE

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LED Control Circuits(3)

CIRCUITS

2. REACTIVE IMPEDANCE CIRCUIT (AC ONLY):Using capacitiveimpedance with a fixed frequency-- Current control with least power consumption-- Minimal heat dissipation-- Improved leading power factor

PRECAUTIONARY MEASURES

Initial charging current may damage LED Fuse for protection of external equipment Low voltage glow protection in certain applications Surge/spike transient protection by MOVs, etc

LVGPMOV

c

FUSE

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WHY LEDs FAIL(1)

USE OF REJECTED LEDs AVAILABLE IN THELOCAL MARKET (Manufacturers reject LEDs

due to defects in the bonding process)

IDEAL BONDING: 50% of the diameter ofthe gold wire is embedded in thesemiconductor

LEDs HAVING HIGH VF

DUE TO CONTACTRESISTANCE AS A RESULT OF INSUFFICIENTBONDING: Such defective LEDs have a highervoltage drop and fail due to overheating

LEDs HAVING HIGH Ir:DUE TO EXCESSIVEBONDING (right through the semiconductor):Such defective LEDs will begin degrading in

light output and generally fail within sixmonths of operation

Semiconductor

Gold Wire

IT IS IMPORTANT TO NOTE THAT EITHER OF THE ABOVE DEFECTS WILL CAUSEEVENTUAL FAILURE OVER A PERIOD OF TIME (NOT NECESSARILY IMMEDIATELY)

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NOISY LINE CONDITIONS, SPARKING IN THE LINE, EMI/RFI, LINE SURGESDUE TO HEAVY MACHINERY OPERATION OR THE EFFECT OF LIGHTNING:

Heavy Current Surges and Spikes Generated Due to Above Can Damage theLED Chips and Lead to Light Degradation

LEDs WITH LOWER LIGHT INTENSITY: Due To Bad Chip Centering, DefectiveOr Bad Encapsulation Of Epoxy, Cracked Epoxy

BAD DRIVER CIRCUIT DESIGN: Improper And Technically Unsound Circuit

Design And High Drive Current Can Cause Premature Failure Of LED

EXCESSIVE HEAT: Deformation of epoxy encapsulation leads to opticaldistortion and permanent fresnel light loss

INCORRECT ASSEMBLY PROCEDURE

Excessive Soldering During Assembly Damages the LED Improper Bending Of LED Leads During Assembly Causes Stress In TheLead Frame

THESE DEFECTS SHOW UP NOT IMMEDIATELY BUT LATER AS A LATENTFIELD FAILURE.

WHY LEDs FAIL(2)

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WHY LEDs FAIL(3)

LONG TERM EXPOSURE TO CONDENSING MOISTURE: This Can Cause The

Epoxy Encapsulation To Deteriorate. Which Will Lead To CatastrophicFailure

INADEQUATE PROTECTION DEVICES: Improper Selection of SurgeProtectors Can Damage LEDs

USE OF COMPONENTS OF INAPPROPRIATE QUALITY: Can Also Cause

Damage to LEDs, Leading to Subsequent Failure of LED

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Blue

Green

Yellow

Orange

White

Red

Amber

W = White (GaN) (x=0.32/y=0.31)

Blue (InGaN) 470nm

Blue-Green (InGaN) 505nm

True Green (InGaN) 525nm

Pure Green (GaP) 560nm

Green (GaP:N) 570nm

Yellow (AlInGaP) 587nm

Orange (AlInGaP) 605nm

Amber (AlInGaP) 615nm

Super-Red (AlInGaP) 630nm

s

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8

blue

green

red

yellow

white

Blue (GaN) 466nm

W = White (InGaN) (x=0.32/y=0.31)

Colour triangle

Colour spectrum of LEDs

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Colour rendering: ~ 80%Colour temperature: > 6000 K

Blue LED + phosphor= white LED

White LEDs

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LUMINIARE EFFICIENCY

Luminiare efficiency of LED is very high upto 90%.

Filament lamps, CFLs, fluorescent tubes,

metal halides are 360degrees emitters whichrely on reflectors to reflect back the light.

Luminiare efficiency of these light sources islow only about 50%, the rest is absorbed inthe luminiare.

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Application Efficiency Luminous efficacy is an important indicator of

energy efficiency, but it doesnt tell the whole story,particularly with regard to directional light sources.

Due to the directional nature of their light emission,LEDs potentially have higher application efficiencythan other light sources in certain lightingapplications. Fluorescent and standard bulbshaped incandescent lamps emit light in alldirections. Much of the light produced by the lampis lost within the fixture,

reabsorbed by the lamp, or escapes from the fixturein a direction that is not useful for the intendedapplication. For many fixture types, including

recessed downlights, troffers, and under-cabinetfixtures, it is not uncommon for 40-50% of the totallight output of the lamp(s) to be lost before it exitsthe fixture.

LEDs emit light in a specific direction, reducing theneed for reflectors and diffusers that can trap light,so well-designed fixtures and systems using LEDscan potentially deliver light more efficiently to theintended location.

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LED DOWNLIGHTERSTOREPLACE CFL.

Today, with higher improved LED technologywe are able to replace a 36W CFL with a 12WLED downlighter, saving 70% energy.

Newer micro-optic Holographic technologyallows use of Micro-lens films to remove glarewith minimal light loss.

Product life 10- 15years. Zero maintenance.