LEDs (Light-Emitting Diodes)
Done by: Lee Liak Ghee (10)
Class: 2i3
Introduction
LEDs, otherwise known as Light-Emitting Diodes, are increasingly
common nowadays. It’s all around us everywhere. Be it traffic
lights, torches, or spotlights, many things around us are beginning
to change from the old filament light bulbs to the new and modern
LED lights. These lights are really bright and powerful, and they
really brighten up the entire place!
Rationale
I have noticed that more and more light bulbs around
us are being replaced by LED light bulbs. Take a look at
the hardware shop: They rarely sell filament light bulb
torches nowadays. Take a look at the traffic lights: They
are now replaced with LED light bulbs instead of
filament light bulbs. Even car lights are also replaced by
LEDs. Why LEDs over filament light bulbs? Why not
continue using the traditional filament light bulbs? Out
of curiosity in these so small yet so interesting light
bulbs, I decided to embark on a research about LED light bulbs and why they are used.
Objectives
In this research I am embarking in, I would like to investigate on LEDs, their application and
the advantages as well as disadvantages of using LEDs as compared to the traditional
filament light bulbs. I would also like to find out how LEDs are made.
Findings
1. What are LEDs? How do LEDs work?
LEDs are Light-Emitting Diodes. As the name suggests, they are diodes that emit light. Before
I move on to Light-Emitting Diodes, I would like to start off by explain about how diodes
work.
Diodes allow current to flow easily on one direction
but not in the other direction. Diodes are made of
semi-conductor materials which are doped to modify
its electrical conductivity properties. Doping a
material means to add impurities into a material so
as to create a P-N junction. A P-N junction has 2
sides: the P side and the N side. The P side has
impurities that will result in the atoms to leave
“holes” in their covalent bonding structure, which is
to be filled up by electrons. The N side however, has
another set of impurities that will result in the atoms
to have spare electrons in their covalent bonding structure. These electrons are the ones
which will allow current to flow easily in one direction (forward-bias), but not in the other
(reverse-bias).
However, this is not what an LED light bulb is mainly used for. LED lights are used for their
function as a light, rather than their function as a diode. These light bulbs, like normal diodes,
require a semiconductor. In order for an LED light bulb to actually emit light, that
semiconductor needs to be made using special materials. The spare electron from the N side
has a lot of energy, and when the current causes the electron to flow and fall into the holes
on the P side, the excess energy is then converted into a photon, which is the light we see
from LED light bulbs. The wavelength of the LED light emitted varies depending on the
materials used to make the semiconductor for the LED light bulb.
The information is compiled into the table below:
Colour
Wavelength
(nm)
Colour
Name
940
880
Infrared
Infrared
850
Infrared
660
Ultra Red
635
633
620
High Eff. Red
Super Red
Super Orange
Super
Orange
Orange
Super Yellow
Super Pure
Yellow
Yellow
"Incandescent"
White
Pale
White
Cool White
Super
Lime Yellow
Super
Lime Green
High
Efficiency
Green
Super
Pure Green
Pure Green
Aqua Green
Blue Green
Super Blue
Ultra Blue
612
605
595
592
585
4500K
6500K
8000K
574
570
565
560
555
525
505
470
430
LED Semiconductor Material
Gallium Aluminum Arsenide / Gallium Arsenide
Gallium Aluminum Arsenide / Gallium Arsenide
Gallium Aluminum Arsenide / Gallium Aluminum
Arsenide
Gallium Aluminum Arsenide / Gallium Aluminum
Arsenide
Gallium Arsenic Phosphide / Gallium Phosphide
Indium Gallium Aluminum Phosphide
Indium Gallium Aluminum Phosphide
Indium Gallium Aluminum Phosphide
Gallium Arsenic Phosphide / Gallium Phosphide
Indium Gallium Aluminum Phosphide
Indium Gallium Aluminum Phosphide
Gallium Arsenic Phosphide / Gallium Phosphide
Silicon Carbide / Gallium Nitride
Silicon Carbide / Gallium Nitride
Silicon Carbide / Gallium Nitride
Indium Gallium Aluminum Phosphide
Indium Gallium Aluminum Phosphide
Gallium Phosphide / Gallium Phosphide
Indium Gallium Aluminum Phosphide
Gallium Phosphide / Gallium Phosphide
Silicon Carbide / Gallium Nitride
Silicon Carbide / Gallium Nitride
Silicon Carbide / Gallium Nitride
Silicon Carbide / Gallium Nitride
It can be seen from this table of semiconductor materials and colours that LEDs require
gallium, aluminum, arsenic, phosphorus, indium, silicon, nitrogen and carbon. The types of
materials used depend on the frequency of the LED light waves needed.
LEDs come in many shapes and sizes, but the most common type of LED light bulbs are the
5mm cylindrical shaped ones (5th from the left). Usually, the colour of the LED light bulb
casing matches the colour of the light itself.
2. What are the advantages and disadvantages of LED technology?
Advantages
Efficient: LEDs emit more light per watt than
traditional filament light bulbs. Shape and
size do not affect its efficiency.
Colour: LEDs are able to emit a light of an
intended colour without the need of using a
colour filter, unlike filament light bulbs. This
helps to increase the efficiency of the light
bulb.
Size: LEDs can be very small (<2mm).
Filament light bulbs are unable to be that
small. They can then be used on circuit
boards for other purposes.
Cool: LEDs radiate extremely little heat when
lighted up, while other lights emit a lot of
heat and infrareds which can damage
sensitive objects.
Dimming: Pulse-width modulation can be
used to adjust the brightness of the LED light
bulb; The filament in filament lights will
remain glowing for a while after the light
switches off.
Lifespan: It has estimated that LEDs have a
lifespan of 35,000 to 50,000 hours;
Fluorescent tubes 10,000 to 15,000 hours;
Filament bulbs 1,000 to 2,000 hours.
Disadvantages
Cost: At the moment, LED technology is
more expensive than other more
conventional lighting technologies in terms
of cost.
Voltage: LED lights need to be supplied with
a voltage above the threshold as well as a
current below the rating. This means that a
series of resistors are needed.
Electrical Polarity: LEDs, being diodes, will
only light up when the electrical current is of
the correct polarity.
Light pollution: LEDs cause more light
pollution than other conventional light
technologies such as sodium vapour lamps.
Blue hazard: Blue LEDs and cool-white LEDs
are capable of exceeding the safe limits of
the “blue light hazard”, and it can harm our
eyes.
3. What are the uses of LED lights?
Low energy consumption, long lifespan as well small size has allowed LEDs to be used in
many indicators and displays on much equipment we see in our daily lives.
Designation signs on buses, traffic lights, watch displays, car lights, and
illumination: It’s all around us. Their applications definitely are not limited to
what has been listed above.
The future holds a lot for LED lights. Due to LEDs being technologically
superior over other types of light like
fluorescent lights or filament light bulbs, its
uses could potentially reach far beyond
what it is being used for now. Sooner or
later LEDs would be used in home lightings and street lights
as well because it is extremely energy efficient and it will
help to reduce the energy usage by a lot. The great potential
behind LED lights has yet to be fully utilized, and it will
surely replace a large portion of the lights we use now in
time to come.
Conclusion
LEDs are getting more and more common nowadays, and there is no doubt that the
advantages outweigh its disadvantages. It’s low energy consumption, together with the long
lifespan it has as well as its ability to emit different coloured lights of our choice makes
people choose LEDs over the traditional filament light bulbs, where its energy consumption
is high, and it also burns out a lot more easily.
Although LEDs are still more expensive than filament lights or fluorescent lights, I believe
that future research and development into this LED technology will enable us to reduce the
disadvantages that current LED technology has, and help us to maximize the potential of LED
lights to its fullest.
References
 http://en.wikipedia.org/wiki/Light-emitting_diode
 http://en.wikipedia.org/wiki/Diode
 http://www.madehow.com/Volume-1/Light-Emitting-Diode-LED.html
 http://www.oksolar.com/led/led_color_chart.htm
 http://en.wikipedia.org/wiki/P-n_junction
 http://ezinearticles.com/?What-The-Future-Holds-for-LED-Lighting&id=789401
 http://spie.org/x42365.xml?ArticleID=x42365
 http://ecoledlight.blogspot.com/