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.
Total Consumption of lighting from four factors in the UK (in
billion lumen-hours), “1700-2000 – Fouquet and Pearson (2007)” (Our World in
In this regard,
increasing the efficiency of electricity based light bulb is the only way to
diminish the tremendous financial lose that we currently experience with
inefficient light bulb.
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 (Passmyexams.co.uk, 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 diode (LED).
LEDs dependent on the InGaN will be used in the future with higher efficiency
and thus leading to the most cost-effective LEDs. Nowadays, people use the
commonly available semi-conductor based LEDs. These LEDs are more beneficial than
incandescent lightbulbs, however less efficient than those of fluorescent. As I
have explained above, LEDs are
currently limited by poor internal quantum and light-extraction efficiency. On
the contrary, the photonic crystals will give the critical and thus potential
solutions to both of the problems.
internal efficiency of InGaN LEDs can be enhanced from the Purcell effect which
is an effect that the more photons are created by placing the emitters inside.
Second way to
improve light energy is by upgrading in the extraction of the light from the semiconductor
chip which has high-index. For normal InGaN LEDs, a large portion of the total energy
is emitted into wave-guided modes to the semi-conductor. 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. Referring to Figure 3, a
photonic crystal can improve the light extraction by diffracting the modes out
of the semiconductor.
Figure 3. Placing a photonic crystal into an InGaN LEDs will increase both the
internal quantum efficiency and the whole amount of light extracted. (Spie.org,
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 unique characteristics of the material which is extremely
hard and chemically stabilized.
Discuss and evaluate:
crystals in GaN will interact with economic factor as the crystals will
increase the efficiency of the LEDs in another term, reducing the total cost
that we need to pay. According to the document made from the Sandia, “they merged
LEDs and photonic-crystal processing to make an electrically-injected InGaN LEDs.”
Figure 4. shows
the emission patterns for both a photonic-crystal and a control LEDs.
The unique pattern
from the photonic-crystal LEDs indicates a triangular symmetry due to the
extraction of wave-guided modes and showed approximately 60% increase of their
efficiency compared to the control.
Figure 4. Two
photos taken from no photonic crystal and photonic crystal (Spie.org, 2018)
from the left and the photonic-crystal LEDs are each very distinct. As the
pattern of photonic crystals shows a scattering of waveguided modes out of the
LEDs chip, it has a strongly-modified emission pattern.
Large portion of
InGaN LEDs performance improvements are still needed, including the increase in
their efficiencies. Photonic crystals have the potential power to dramatically
increase efficiency of InGaN LEDs, “a big step towards producing white-light at
of approximately 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.
efficiency of a LEDs will be at its best state when photonic crystals enhance
the efficiency via Purcell effect and by improving in the extraction of the light.
With the improvement in the efficiency, we will be able to save more money than
ever which will also result saving our planet, Earth.