An optical head-mounted display (OHMD) is a wearable device that has the capability of reflecting projected images as well as allowing the user to see through it, similar to augmented reality technology.

1. Optical display

2. ABOUT ME
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3. HISTORY
• Cathode ray tube was discovered by Johann Hittorf in
1869 in primitive Crookes tubes.
•He observe that some unknown rays were emitted
from the cathode which could cast shadows on a
glowing wall of tube.
• In 1890, Arthur Schuster and William Crookes
demonstrated cathode ray could be deflected by
electric field and magnetic field respectively. In 1907
Boris Rosing used CRT in the receiving end of an
experimental video signal to form a picture

4. WHAT IS
CATHOD
E RAY
TUBE?
The cathode ray tube (CRT) is a vacuum tube
containing an electron gun (a source of
electrons) and a fluorescentscreen, with
internal or external means to accelerate and
deflect the electron beam.
A fluorescent screen coated with fluorescent
material to show images from X-ray.

5. How CRTS work and display?
A CRT monitor contains millions of tiny red green and blue phosphorus dots
that glow when struck by an electron beam that travels across the screen to
create a visual image in a CRT monitor tube the cathode is a heated filament
the heated filament is a vacuum created inside a glass tube the electrons are
negative and the screen gives a positive charge so the screen glows

6. BASIC CATHOD RAY TUBE
The CRT uses and evacuated glass envelope which is large deep heavy and
relatively fragile

8. LCD
Also Know as Liquid crystal display
• Liquid crystal display is a thin flat panel display deice
used for electronically displaying information such as
text , images and moving pictures.
• LCD is used in computer monitors Televisions
Instrument panes, Gaming devices etc.
• Polarization of light is used here to display objects.

9. Liquid crystals
• Liquid crystals are liquid chemicals in a state
that has properties between those conventional
liquid and solid crystals .That is a liquid crystal
may flow like a liquid but its may be oriented in
a crystal like way.
• Liquid crystal molecules are aligned precisely
when subjected to electric fields as like as in he
way metal shaving line up in the filed of a
magnet .When properly aligned , the liquid
crystals allow light to pass through

10. The most popular liquid
crystal structure is the
noematic liquid crystal
NLC when they are in a
pneumatic face liquid
crystals are a bit like a
liquid their molecules can
move around and shuffle
paste one and other but
they all point in broadly
the same direction
The liquid is normally
transparent but if it is
subjected to a strong
electric field ions moves
through it and disturb the
well ordered crystal
structure causing the
liquid to polarize and
hence turned off opaque
the removal of the applied
field along the crystal
structure to the form and
the material regains its
transparency

11. The polarization property of light is used in LCD screen to
switch its colored pixels of on at the back of the screen there is
a bright light that shines out towards the weavers in front of
this there are the millions of pixels each one made up of
smaller area called Sub pixels they are colored red green or
blue
Each pixel has a polarizing glass filter behind it and another in
front of it at 90°

12. Liquid crystals can adopt a twisted up structure and when we
apply electricity to them they straighten out again this is the key
how LCD display turn pixel
on and off

13. • In between the two polarizing
filters there is a tiny twisted
noematic liquid crystal that can be
switched on or off electrically
• When it is switched on it rotates
the liquid pass through it through
90° effectively not allowing light to
flow through the two polarizing
filters and making the pixels look
dark

14. Each pixel is controlled by a separate transistor that
can switch it on or off many times each second .
It also very the amount of light that pass hence
giving different shades of red blue green to each
Pixels.
Which in result collectively from a image.