Introduction: heat energy output are our goals. On


We currently live
in a society where people are required to work more no matter it is a day or a night.
As more population tend to stay in their office or their factories for work, there
is an increase in the use of the light bulb. Some might think that damages
formed from increased usages in offices and factories do not apply or give impacts on our planet,
Earth. On the contrary, escalating use of inefficient light bulbs will result
damaging us not only financially but also other factors which can lead to serious
condition. As referring to Figure 1, the main portion of total lighting is
electricity and its usage is kept increasing. 

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Consumption of lighting from candles, gas, kerosene and
electricity in the United Kingdom (in billion lumen-hours), 1700-2000 – Fouquet
and Pearson (2007) (Our World in Data, 2018)


In this regard,
increasing the light bulb’s efficiency is the only way to diminish the tremendous
financial lose that we currently experience with inefficient light bulb.



Brief description:

Learning the way
to calculate the efficiency of the light bulb is the basic step for us to find the
methods to increase the efficiency. As the Figure 2 describes, we can calculate the efficiency by finding the values
for total electrical energy input, light energy output (useful), and heat
energy output (waste).


Figure 2. the
formula for efficiency (, 2018)


To summarize the points, increasing the
light energy output and decreasing the heat energy output are our goals.


On the contrary,
there are some quantities that we first need to consider in order to improve
the efficiency. Those are the heat energy, poor internal quantum, and
light-extraction efficiency in the light bulbs. From these, we experience the
loss in useful light energy when heat energy increases and it results having
descent efficiency. And as most LEDs are not able to extract light efficiently
due to poor internal quantum, there would be total decrease in light bulb efficiency.




By far, the most popular
and commonly used light bulbs available are light-emitting diodes (LEDs). LEDs relied
on indium gallium nitride (InGaN) will be used in future high-efficiency
lighting instrument. Currently-available semiconductor-based LEDs are more
efficient than incandescent lightbulbs but less efficient than those of fluorescent
tubes. As I have explained above, LEDs
are currently limited by poor internal quantum and light-extraction efficiency.
However, the photonic crystals give the critical potential solutions to both of
the problems.


First, the
internal efficiency of InGaN LEDs can be enhanced from the Purcell effect, in
which the more photons are generated by placing the emitters inside.


Second way to
improve light energy is by upgrading in the extraction of the light from the
high-index semiconductor chip. For normal InGaN LEDs, a large portion of the
energy is emitted into wave-guided modes internal to the semiconductor. Light
generated inside the semiconductor bounces around due to internal reflection, and
there is a high opportunity that the light particles will be absorbed before it
escapes from the semiconductor. A photonic crystal can improve light extraction
by diffracting the modes out of the semiconductor.


1 shows a diagram of a photonic crystal LEDs.

Figure 1. Incorporating a photonic crystal into an indium-gallium-nitride LEDs
increases both the internal quantum efficiency and the amount of light
extracted. The light is produced in the QW active region. (, 2018)


On the contrary,
the limitations that can be made for the modifications are difficulty of
fabricating the photonic crystals in GaN. The process is a quite complicated
due to difficulty of etching the material which is extremely hard and
chemically inert.


Discuss and evaluate:

The photonic
crystals in GaN will interact with economic factor as the crystals will
increase the efficiency of the LEDs in another term, reducing the cost. According
to the document made at Sandia, they combined LEDs and photonic-crystal
processing to make an electrically-injected InGaN LEDs. Figure 3. shows the emission patterns
for both a photonic-crystal and a control LEDs. 

photonic-crystal LEDs pattern shows a triangular symmetry due to the extraction
of wave-guided modes and showed a 50% increase in efficiency compared to the

Figure 3. Far-field emission patterns from a left and a photonic-crystal LEDs
are very each very distinct. The latter has a strongly-modified emission
pattern due to the scattering of waveguided modes out of the LEDs chip.

(, 2018)


Many InGaN LEDs
performance improvements are still required, including increased efficiencies, and
higher power lamps. Photonic crystals have the potential to dramatically
increase InGaN LEDs efficiency, a first step towards producing white-light at
of 200lm/W.


Some might say
that the fabrication of photonic crystals in GaN is challenging and will
require a lot of efforts for producing the modified LEDs. However, the amount
of saving will be the most efficient economically in a long-term due to
dramatic increase in InGaN LEDs efficiency.  



Brief conclusion:

Thus, the
efficiency of a LEDs will be at its best state when photonic crystals enhance
the efficiency via Purcell effect and by assisting in the extraction of light
from the high-index semiconductor chip. With the improve in the efficiency, we
will be able to save more than ever which also will result saving our planet,