LEDs emit light when connected in a circuit and come in different colors depending on the semiconductor material. LCDs use liquid crystals to control the transmission of light and are used in displays. Lasers produce highly directional, coherent light through stimulated emission and are used for applications like optical communication, reading, and printing due to their small size, efficiency and ability to be modulated at high frequencies. LEDs, LCDs, and lasers each have distinct operating principles and applications in lighting, displays, and other technologies.

1. LASER, LED,LCD display

2. What’s So Different?
Incandescent Lamp only around 10% of the energy is
used to make visible light.

3. INTRODUCTION
A light-emitting diode (LED) s are special diodes
that emit light when connected in a circuit.
 Amount of light output is directly proportional to
forward current

4. SC materials – Gallium Phosphide (red or green)
Gallium arsenide Phosphide(red or
yellow)
Gallium arsenide ( infrared)
Gallium nitrite (blue)

5. Anatomy of an LED

6. Contd..• The negative side of an
LED lead is indicated in two
ways: 1) by the flat side of
the bulb, and 2) by the
shorter of the two wires
extending from the LED. The
negative lead should be
connected to the negative
terminal of a battery .

7. COLOUR OF LED
The colour of the light (corresponding to the energy
of the photon) is determined by the energy gap of the
semiconductor.
LEDs are designed to operate with no more than 30–
60 milliwatts of electrical power.

8. ADVANTAGES
Lower energy consumption
Longer lifetime
Improved robustness
Smaller size
Faster switching

9. DISADVANTAGES
 LEDs powerful enough for room lighting and are
relatively expensive.
It requires more precise current and heat
management than compact fluorescent lamp sources
of comparable output.

10. APPLICATIONS
Light-emitting diodes are used as
Low current LED –low power dc circuits,
telecommunication indicator, portable equipment,
keyboard indicator
Automotive lighting
Traffic signals
Infrared LEDs are also used in the remote control
units of many commercial products including
televisions, DVD players, and other domestic
appliances.

11. How LED Lighting Distinguishes
Every Application Area
LEDs in Retail Environments
provide a wide range of effects – from the strikingly
dramatic to the intriguing and inviting – that
contribute to the total shopping experience.
highlight a product, create drama and interest, but it
can also reflect mood, helping create the perfect
environment for the shopping experience.

12. LEDs in Office Environments
uniform level of illumination throughout.
Reflections on computer screens can prove tiring as
the day draws on, and as concentration drops, so does
efficiency.
 making people feel more comfortable at work and
stimulating their performance – but also considerable
energy and maintenance cost reductions.

13. LEDs in Hospitality Environments
Lighting a hotel or restaurant is a complicated
business.
Hotels, for example, need to have lighting 24/7 – in
corridors and hallways, for example, or in reception.
Yet the lighting must also be adaptable, capable of
creating a wide range of moods to make the guest feel
welcome, safe and comfortable.
LED solutions can make guests feel comfortable, at
home. And do it while offering enormous savings in
maintenance and energy-costs. LED solutions can
create an ever-changing palette of moods, each tailor-
made for a specific moment, a specific use.
low maintenance such systems required thus greatly
reducing running costs.

14. LED in Outdoor Environments
The needs of urban lighting are changing.
creating flexible ambiances that could, for example,
change with the weather or the season, and provide
an extra festive color on public holidays.
energy consumption that is only a fraction of
conventional lighting techniques.

15. How an LCD works
An array of Liquid Crystal segments
–When not in an electrical field, crystals are organized in a
random pattern
–When an electric field is applied, the crystals align to the
field
–The crystals themselves do not emit light, but ‘gate’ the
amount of light that can pass through them
•Crystals aligned perpendicular to a light source will prevent
light from passing through them
Each LCD segment is aligned with an electric field
A light source (backlight) is needed to drive light through
the aligned crystal field

16. Twisted Nematic (TN) Displays

17. Passive LCD panels
Active LCD
panels

18. Passive LCD panels
–Consists of a grid of row and columns electrical
signals
–Columns and rows connect perpendicularly to every
segment in the LCD
•Columns and rows are multiplexed to many different
segments
–An IC controls which column and row are selected to
enable or disable the segment at the row/column
intersection
–A small bias is applied to the row and column to
generate a field at the intersection
•No charge is stored at the segment
•It may take multiple passes to correctly align the field
to the desired value

19. Active LCD panels
–Consists of a grid of row and columns electrical
signals
–Columns and rows connect perpendicularly to a
active device (transistor) for every segment in the
LCD
•Columns and rows are multiplexed to many different
segments
–An IC controls which column and row are selected
to enable or disable the segment at the row/column
intersection
–The selected row and column enable the transistor
•Charge is stored at the transistor
•One pass will set the aligned state of the transistor
(although it may still take a little time for all the

20. Construction
two glass plates with some liquid crystal material
between them
Types
Dynamic scattering LCD
Field effect LCD

21. Dynamic scattering LCD
Transmittive type cell
Reflective type cell

22. Reflective type cell

23. Field effect LCD

24. Field effect LCD

25. Advantages

26. Disadvantages

27. Application

28. LASER INTRODUCTION
Light Amplification by Stimulated Emission of Radiation
 The Laser is a source of highly directional,
monochromatic, coherent light.
The unique property of laser is that its light waves travel very
long distances with every little divergence
Laser diode is similar in principle to an LED.
Case of a conventional e source of light, the light is emitted
in a jumble of e separate waves that cancel each other at
random and hence can travel very short distances only.
concentration of its energy to extremely high intensities, the
intensity remaining almost constant over long distances
because of low divergence.

31. Types
Surface emitting laser diodes
Edge emitting laser diodes

32. ADVANTAGES
The semiconductor laser differs from other lasers (solid,
gas, and liquid lasers):
 small size (typical on the order of 0.1 × 0.1 × 0.3 mm3)
 high efficiency
 the laser output is easily modulated at high frequency
by controlling the junction current
 low or medium power (as compared with ruby or CO2
laser, but is comparable to the He-Ne laser)
 particularly suitable for fiber optic communication

33. COMPARISION
Laser Diode
 Stimulated radiation
 narrow line width
 coherent
 higher output power
 a threshold device
 strong temperature
dependence
 higher coupling
efficiency to a fiber
LED
 Spontaneous radiation
 broad spectral
 incoherent
 lower output power
 no threshold current
 weak temperature
dependence
 lower coupling
efficiency

34. APPLICATIONS
 Optical-fiber communication
 Video recording
 Optical reading
 High-speed laser printing
 High-resolution gas spectroscopy
 Hologram scanners

35. Draw mindmap

36. MIND MAP
36
LCD LED Laser
construction
applications Advantages

37. Summary
LED,LCD, LASER
Definition
Construction
Principle
Advantages
Application

38. Multiple choice question
 The Laser operates under a ___________ process.
A) stimulated emission b) unstimulated emission
c) Emission d) discharge
 Which is not the application of laser diode
a) Optical-fiber communication
b) Video recording
c) Optical reading
d) low -speed laser printing