About LED

2.  Light emitting diode.
 Semiconductor device.
 Led converts electrical energy into light
energy.
 It is a monochromatic occurring at
single wavelength.
 Output from LED ranges from 700nm is
red , blue is 400 and infrared is 830nm.

3.  LED consists of p-type and n-type
semiconductor material.
 These are placed in a direct current
forming a p-n junction.
 It works only in forward bias condition.
 Free electrons in the conduction band
recombines with holes in valance band
and releases energy in the form of light.
 Construction of the LED is similar to
normal p-n junction diode where
phosphorus and arsenic materials are
used for construction instead of
germanium and silicon material because
Si and Ge does not exit energy in the
form of heat.

4. Voltage is
applied
• Electrons moves in one
direction across the
junction i.e. electrons in
the n region move across
the p region towards the
junction
conversion
• Electric potential
energy is converted
into electromagnetic
energy
• Energy is converted in
the form of photon
expression
• E=qV Joules
• Energy of one
electron is -
1.6x10˄-19c

5.  As the LED is to be connected in a
forward bias condition across a power
supply should be limited using a
series resistor to protect it from
excessive current flow. Never connect
an LED directly to a battery or power
supply .
 Forward voltage drop across the PN
junction and this parameter which is
determined by the semiconductor
material used, is the forward voltage
drop for a specified amount of
forward conduction current, typically
for a forward current of 20mA.

6.  Sensor application
 Mobile application
 Signals
 Calculators
 Watches , camera
 Multimeters
 Fiber optic data
communications

7. OLEDs
QUANTUM DOTS
INFRA RED

8. LEDs are 5 times more efficient
than other fluorescence bulbs
Same amount of light with less
energy
LEDs have larger life span
Typical life spans of LEDs are
30,000-100,000 hours where the
others are last only for 750-2000
hours
Led operates near 90˚F others
are operate between 150-400˚F
LEDs contain no harmful gases
and mercury so it is
environmentally friendly
Very cheap and light in weight

9. Colour
Wavelength
[nm]
Voltage drop [ΔV]
materials
Infrared λ > 760
Gallium arsenide (GaAs)
Aluminium gallium arsenide (AlGaAs)
Red 610 < λ < 760
Aluminium gallium arsenide (AlGaAs)
Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium
phosphide (AlGaInP)
Gallium(III) phosphide (GaP)
Green 500 < λ < 570
Traditional green:
Aluminium gallium phosphide (AlGaP)
Pure green:
Indium gallium nitride (InGaN) / Gallium(III)
nitride (GaN)
Violet 400 < λ < 450 Indium gallium nitride (InGaN)
Purple Multiple types
Dual blue/red LEDs,
blue with red phosphor,
or white with purple plastic
White Broad spectrum
Cool / Pure White: Blue/UV diode with
yellow phosphor
Warm White: Blue diode with orange
phosphor