LED`s......
History of LED
Let
us look at this journey of LEDs through which they triumphed over the Lighting
world.It was 1962, when Nick Holonyak Jr. invented first visible led, emitting
red light, while working at General Electric. As the light output of these
LED’s was not enough to illuminate the surrounding area, but were good enough
to be used as indicators and hence Indicators, seven segment displays were some
initial applications followed by being used in appliances such as calculators,
watches, TV, telephones.
With
the help of similar alloys, more colours green, yellow were manufactured by mid
1970’s.
The
ongoing research in LED technology brought superior ones with improved
efficiency and light output. 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.
With
improved performance, applications and market penetration began to rise. By
early 1990’s High brightness LED packages were developed and were widespread
used in Traffic lights.
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
Inside
the little light House:
The way these tiny blinkers light up
is far different from the traditional counterparts. For understanding its
outstanding capabilities, we need not dig deep but just our fundamental
concepts of Semiconductor diodes.
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 a hole which exists at a lower energy level
than electron, because of this an electron loses some energy which is released
in the form photon and hence light is emitted. This phenomenon is termed as
Electroluminescence.
Now this emitted light may or may
not fall in the visible spectrum depending on the material of semiconductor. In
silicon diode, the energy gap is not much wide and hence the emitted photon of
low frequency is falls in infra red region (Infra Red LEDs). But in case off
our little blinkers, the semiconductor material used is Aluminium Gallium
Arsenide (AlGaAs) and later on various similar alloys. The colour of emitted
light depends on the energy gap of semiconductor.
Creating
White Light:
LEDs are not white light sources.
They are highly efficient monochromatic light emitters, which is the reason
they rule the coloured light applications such as traffic signals, exit signs
etc.
For LEDs to be used for general
purpose illumination, white light is needed. Mainly, there are two ways of
achieving white light from LEDs:
· Mixing of
monochromatic lights red, green, and blue to white light.
In this method, multiple wavelengths
(RGB) are mixed to produce light. This technique is same as employed in
television sets in which a white spot is created using red, blue and green
light in proper proportion.
The creation of white light by
mixing colours has additional advantage of tuning it to a specific colour
temperature to look warm or cool. The Colour temperature rating of a lamp is a
general ‘coolness’ or ‘warmth’ measure of its appearance, termed as Correlated
Colour temperature. It is measured in Kelvin. The white led spectrum ranges
from 2540K-10,000K. Cool white, warm-white, neutral-white are some of the categories
depending on varying colour temperature. Designers can choose the suitable
colour temperature as required. Lamps above 4000K are generally categorised as
‘cool’ while those below 3200K as ‘warm’ in appearance.
· Second method is
Phosphor conversion, in which a phosphor is used on or near the LED to emit
white light. This method uses a blue Indium-Gallium-Nitride (InGaN) LED with a
phosphor coating to create white light. The coating emits a yellow light when
the blue light from the LED shines on it. The mix of the yellow light with the
blue light forms a white light. This is the method that results in the more
commonly seen “white LED”. It is the amount of inefficiency in phosphor
conversion due to some energy loss in the conversion that makes white light
LEDs less efficient than coloured LEDs.
LED
(SSL) - What makes me Unique??
The little blinker is glowing on
famous buildings, bridges, hotels all over the world. This is indeed a
remarkable advancement, as it not just evolved and changed but is now changing
the way world lights up!
Solid State Lighting is realized
when LEDs are combined with well designed luminaries. Let us dwell into depth
and find the factors that made the buzz of Solid State Lighting all around.
So what made LEDs to be used for
general illumination purpose? LEDs being inherently monochromatic light sources
were not even considered as an option for general lighting purpose (which
requires a dedicated white light source) until Shuji Nakamura invented the high
brightness blue LED, which can be used to produce white light. Since then,
there has been noteworthy improvement in the performance of white light LEDs.
Light output, control, efficacy, optical design, lifetime have been improved to
make them competent with conventional light sources. Also, the increasing
efficacy (the amount of light provided in lumens, per watt of electricity
consumed (lm/W) in last decades has contributed significantly for the same. The
energy performance of LEDs is continuing to improve dramatically and has
approached 100 LPW in the production of white LEDs. The development of LED
technology has caused their efficiency and light output to increase
exponentially, with a doubling occurring about every 36 months since the 1960s,
in a way similar to Moore's law.
The following factors focus on some
more reasons for wide acceptance of SSL.
· Energy Efficiency
At a time of escalating energy
crisis, the less efficient sources are bound to move out of the market replaced
by more efficient solutions. Same is the fate of incandescent sources. LEDs can
cut the general lighting energy use by one quarter.
Energy Star rated LEDs use at least
75 percent less energy than traditional incandescent bulbs and last 25 times
longer, according to the U.S. Department of Energy. A 1.3-watt LED bulb uses
less electricity than both the 60-watt incandescent and the 9-watt CFL bulb.
The way LED produces light does not involve energy loss as heat while
Incandescent and CFLs release most of their energy as heat, 90 percent and
80 percent, respectively.
LED lighting will eventually replace
halogen bulbs. It is said that a typical 50 watt halogen lamp will produce 22
lumens per watt of energy that is produced. As well as this, the bulb will last
for around 2,000 hours. When we compare this will a typical LED light, it will
actually produce the same amount in terms of lumens but it will only take 7
watts. This is a huge energy saving. As well as this, the bulb will last 50,000
hours compare with 2,000.
US Department Of Energy’s
long-term research and development goal calls for white-light LEDs producing
160 lumens per watt in cost-effective, market-ready systems by 2025
· Go SSL- Go Green!
The little energy savers do make a
BIG difference, having the potential to cut general lighting energy uses by one
quarter saving energy dollars and carbon emission too.
The annual Co2 reduction is much
significant even for a single bulb. The feather in the cap is its long life.
Moreover, it does not contain mercury like CFLs. In many applications, the
reduced energy requirement extends the running time of battery operated devices
like notebook computers, mobile phones and also reduces petrol consumption and
CO2 emissions. Also, their long lifetime minimizes service requirements in many
applications.
· Directional Emission
One of the unique characteristics of
LEDs is their directional light emission. When light is emitted in specific
direction, it reduces the need of reflectors and diffusers to trap light.
Fluorescents and incandescent emit light in all directions, out of which some
amount is lost within the fixture, escapes out in unintended directions or get
reabsorbed. In some cases even 40-50% of energy gets lost even before it exits
the fixture.
While in case of LEDs, cleverly
designed fixtures can deliver light efficiently in intended direction, for
example, LED strip lights can be installed under counters, in hallways, and in
staircases; concentrated arrays can be used for room lighting.
· Long,LongLife
Now you don’t need to change the
bulbs or CFL again and again, go the LED way and forget to change it for next
20 years!! Sounds imaginary...Right?
Here unveils one more miracles of
LEDs. The life of incandescent lamp is about 1000 hours and that of a CFL
is nearly 8000 to 10,000 hours. On the other hand, LEDs offer much higher
lifetime of 30,000 to 50,000 hours in well-designed fixtures. Some claims even
go higher up to 70,000 hours with 70% lumen maintenance.
LED lights are more rugged and
damage-resistant than compact fluorescents and incandescent bulbs. Also, LED
lights don't flicker.
Not only it lives longer, but
reduces your electricity bills up to 7%
Lighting
Quality
The quality of lighting can be
evaluated on certain parameters like:
· Colour Appearance: i.e. whether a white light
appears more yellow/gold or more blue. It is measured by Correlated Colour
Temperature (CCT), which is a specification of the colour appearance
of the light emitted by a lamp, relating its colour to the colour of light from
a reference source it is measured in Kelvin scale. For most interior
lighting applications, warm white (2700K to 3000K) and in some cases neutral
white (3500K to 4000K) light is appropriate.
· Colour rendering
Index: CRI is a
measure of the degree of colour shift objects undergo when illuminated by the
light source as compared with those same objects when illuminated by a
reference source of comparable colour temperature. Generally, a CRI of 70 and
above will be required for most lighting applications. The leading
high-efficiency LED manufacturers now claim a CRI of 80 for phosphor-converted,
warm-white devices but the CRI of RGB LED system has found to be inaccurate.
Applications
The substantial progress in SSL has
made headway for its use in diversified applications.
· Industry: Industrial sites operating
24/7 consumes huge amount of energy. Also, it becomes very tedious and affect
the operation too when the lamps need to be replaced in their super high
ceilings. Of course, a solution that does not need frequent maintenance and
reduces energy consumption without compromising the light level is worth opting
for.
· Offices: SSL moves parallel to the changing
tastes in world class design. They provide freedom to choose different
shapes, designs, dynamic effects in intensity and direction, colours. They
effectively create better work places along with significant energy savings,
especially when combined with lighting controls.
· Retail: They are increasingly used for
retail outlets as they can be used to create suitable scene for every occasion,
be it highlighting a product or create perfect shopping environment by
employing effects to enhance the shopping experience.
· Outdoor Spaces: LEDs provide an unparalleled way of
illuminating our urban environment in an exciting and practical manner. They
are highly adaptable, allowing designers to move away from the static lighting
of the past and venture into creating flexible ambiances that could, for
example, change with the weather or the season, and provide an extra
festive colour on public holidays. And all this with energy consumption that is
only a fraction of conventional lighting techniques.
Challenges
The upfront cost of LEDs is the
major challenge faced by SSL for coming to general house hold lighting
applications. LEDs can cost two to six times the price of CFLs.
Good-quality LED products currently carry a significant cost premium compared
to standard lighting technologies. However, with ongoing research advancements
and increased acceptance in various applications, the costs are coming down.
Less brightness is also an issue, but ongoing research has even started
suggesting promising solutions for it too. Organic LEDs and nanotechnology are
offering better and much improved solutions.
OLEDs:
The Bright ‘Organic’ Future
Even after the giant leap, the
little LEDs still have long way to go. After wide acceptance for inorganic
LEDs, it’s time to explore the ‘Organic’ way.
New research is focussing on
alternative materials like organic polymers to develop what are called as
Organic LEDs. These LEDS are not just eco-friendly to dispose of, but also
generates photons of various wavelength ranges to help to produce white light.
New improved designs are also being developed to produce much bright white
light.
Another proposed technique for
brighter LEDs is Nano-imprint lithography to directly imprint the holes,
imperceptible to the human eye, onto the LEDs allowing more of the light to
escape. By making microscopic holes on the surface of the LEDs it is possible
to extract more light, thus increasing the brightness of the lights without increasing
the energy consumption.
Their unique characteristics like
lack of infrared or ultraviolet emissions, long life and ease of maintenance,
good performance in cold temperatures, resistance to breakage and vibration,
compact size, and instant-on performance make them the inevitable option for
tomorrow.
We await the new Energy Efficient
and Eco friendly solution to light up the globe.