Light Emitting Diodes

Light Emitting Diodes Instrumentasi dan Mikroproses

CHARACTERISTICS OF LEDs • • • •

light can be directly generated very compact and lightweight packages mechanically very robust can tolerate even severe mechanical shocks, the color tone can be adjusted by adjusting the relative operation currents. • Dimming is possible – reducing the current – quickly switching with a variable duty cycle

Tri-Colour LEDs • red and a green LED combined in one package • mixed red and green light appears to be yellow • centre lead (k) is the common cathode for both LEDs • the outer leads (a1 and a2) are the anodes

Bi-Colour LEDs • two LEDs wired in 'inverse parallel' • one of the LEDs can be lit at one time

list of the material with the colour that can be produce Material

Acronyms

Color

Aluminum Gallium Arsenide

AlGaAs

Red

Gallium Aluminum Phosphide

GaAlP

Green

Gallium Arsenide Phosphate

GaAsP

Red

Gallium Nitride

GaN

Green

Gallium Phosphide

GaP

Yellow

Zincum Selenide

ZnSe

Blue

Indium Gallium Nitride

InGaN

Blue

Indium Gallium Aluminum Phosphide

InGaAlP

Orange

Silicon Carbide

SiC

Blue

Carbonium

C

Ultra-violet

Silicon

Si

Blue

Alumninium Oxide

Al2O3

Blue

Emission Properties • has a low spatial coherence • the focus ability (beam quality) is very low • emission bandwidth is typically some tens of nanometers (e.g. 40 nm) or even > 100  nm

Device Lifetime • • • • •

can have very long lifetimes exceed 100 000 hours relatively sensitive to excessive reverse voltages can be destroyed by electrostatic discharge lifetime is severely reduced for operation with a too high current and/or at too high ambient temperatures

Electrical Characteristics • A reverse voltage of a more than a few volts can destroy an LED • In the forward direction, current remains very small for low voltages and then rises very quick with increasing voltage

CONSTRUCTION OF LED • 'standard' LED has a round cross-section of 5mm diameter • Standard LEDs have a viewing angle of 60° • the emission color of an LED are largely determined by the band gap energy of the semiconductor material used.

Process of Color Emitting • In zero bias, high potential barriers prevent the electron to travel freely. • no light emitted from the LED.

Process of Color Emitting cont… • In forward bias, low potential barrier gives the electron chance to travel and fall into the hole • it radiates an amount of energy in term of light

Application of LEDs • Traffic light • Electronic billboard • Emergency vehicle lighting • Flash light • Backlight • Grow-light

Traffic light • Brighter • LED bulbs are last for long years • save a lot of energy.

Electronic billboard • low production costs • can deliver an adaptable messaging method • attract the consumer with the instant turnaround.

Emergency vehicle lighting • can be seen during the day time

Flash light • more efficient at low power level • save more batteries

Backlight • LED backlight was thinned and lighter • requires less energy

Grow-light • relatively cheap • bright enough for the plant to grow • only emit the light colors that needed for the plan to grow • did not use too much power.

Advantages of Using LEDs • high efficiency - it produces more light per watt • can emit light without the use of colour filters • very small size and easily populated onto printed circuit boards • light up very quickly • radiate very little heat in the form of IR • relatively long useful life • difficult to damage with external shock • not a toxic matter

DISADVANTAGES OF USING LED • more expensive • depends on the ambient temperature of the operating environment • Voltage sensitivity • Light quality • Blue Hazard