2. Q.1 Explain the principle of operation of Light Emitting Diodes?
ANS :- Working of LED’s.
A P-N junction can convert absorbed light energy into a proportional electric current. The
process is reversed here called electroluminescence, which can be defined as the emission of
light from a semi-conductor in the presence of an electric field. The charge carriers recombine in
a forward-biased P-N junction as the electrons cross from the N-region and combine with the
holes at the P-region. Free electrons are in the conduction band of energy levels, while holes are
in the valence energy band. Thus the energy level of the holes will be lesser than the energy
levels of the electrons. Some portion of the energy must be dissipated in order to recombine the
electrons and the holes. This energy is emitted in the form of heat and light.
The electrons dissipate energy in the form of heat for silicon and germanium diodes but in
gallium arsenide phosphide (GaAsP) and gallium phosphide (GaP) semiconductors, the electrons
dissipate energy by emitting photons. If the semiconductor is translucent, the junction becomes
the source of light as it is emitted, thus becoming a light-emitting diode, but when the junction is
reverse biased no light will be produced by the LED and, on the contrary, the device may also be
damaged.
3. Q.2 Mention are the series of advancements in LED’s?
ANS:
SERIES OF ADVANCEMENT IN LED’S
1. 1960s -LED’S used to emit RED Light.
2. 1970s -LED’S able to emit GREEN, YELLOW & ORANGE light. Used in Calculators,
digital watches and displays.
3. 1980s -Improvement in light output. A 10x increase in brightness.
4. 1990’s - Used in Traffic lights.
5. Now a days- LED’S have achieved efficiency of 100Lm/W D
4. Q.3 Enumerate on the different types of LED’s?
ANS: There are a number of major types of LED which are available and being developed.
These LED types are summaries below :-
1) Traditional inorganic LED’s : It is manufactured from inorganic materials. Some of the more
widely used are compound semiconductors such as Aluminium gallium arsenide, Gallium
arsenide phosphide, and many more.
2) Organic LED’s : The organic type of LED display is based on organic materials which are
manufactured in sheets and provide a diffuse area of light. Typically a very thin film of organic
material is printed onto a substrate made of glass.
3) High Brightness LED’s : High brightness LEDs, HBLEDs, are a type of inorganic LED that
are starting to be used for lighting applications. This type of LED is essentially the same as the
basic inorganic LED, but has a much greater light output. To generate the higher light output,
this LED type requires to be able to handle much higher current levels and power dissipation.
5. Q.4:- What are the application areas of LED’s?
ANS: LEDs are utilized in many industries for many things. The applications of this efficient and
environmentally-friendly light source are endless, however, there are 5 main fields of
application:
1) Automotive : Uses for the interior of automobiles include indicator lights on dashboard
gauges, audio status lights, security status lights and warning signals. Automobile
exterior usage includes third brake lights, the left and right rear lamps, turn signals, etc.
Currently many European series vehicles including Audi and BMW integrate high
power LEDs.
2) Backlight sources : The mobile phone is the largest market of integration for SMD
(surface mount diode) LEDs. An estimated 400 million mobile phones are sold annually.
One mobile phone takes two LED backlight sources and six SMD LED key lights. As a
result, mobile phones create a demand for 3.2 billion LEDs per year.
3) Display Screen : The LED screen has become the new display medium for advertising
and information. It is commonly used in concert, arena and trade show venues. Its
popularity has prompted the rapid technological development of large-scale integrated
circuits. Compared to plasma- and LCD-based displays and traditional media such as
6. neon lights, LED displays offer advantages such as high brightness, dynamic visual
display, high reliability, low energy consumption, long service life, display content
diversity, high durability, and low maintenance costs.
4) Electronic Equipment :Due to attributes such as low power consumption, small size, and
long life, LEDs have become the preferred light source on various electronic equipment.
Today, LEDs have been integrated as warning lights and indicators on most electronics.
7. 5)General Lighting : LEDs are being used in advertising billboards, illumination of
commercial building exteriors, landmark buildings, bridges, roads, town centers and
landscape lighting because of the numerous advantages they offer. Their long life, rich
color, and easily-controlled features with integrated electronics offer a scalable lighting
solution.
Q.5 Develop a case study on the amount of energy saving and cost thereof which you will end up
saving if you replace all the bulbs/incandescent tubes in your house with LED’s on the pattern
discussed in class with calculations.?
ANS: My house contains cfl=15 and bulbs=5.
Power rating of bulb=100watt
Power rating of cfl=15watt Power rating in led=6 watt
Power consumption of cfl in 1 day(8 hours of use)=15x15x8=1.8kwh
Power consumption of led=6x6x8=0.288kwh
Power consumption of bulb=5x5x8=0.200 kwh
Power consumption of cfl in 1 month=15x15x8x30=54 kwh
Power consumption of bulb in 1 month=5x5x8x30=6kwh Power consumption of led in 1
month=6x6x8x30=8.64 kwh.
Total consumption cfl and bulb=60 kwh Energy efficiency=60-8.64=51.36 kwh Cost
effectiveness=51.36x7=359.52 rupees.
