1. Direct-View Storage Tubes
This is the method for maintaining a screen
image by storing the picture information
inside the CRT. Similar to the standard CRT,
except that it does not need to be refreshed
because its stores picture information as a
charged distribution just behind the screen.

2. Flood Electrons
Flood Storage
Gun mesh grid
Phosphors
Screen
Writing Collector
Writing
Beam Gun Beam

3. Two electron guns are used in DVST.
One, used to store the picture pattern.
Second, the flood gun, maintains the picture display.
The electron beam is designed not to write
directly on the phosphors but on a fine-mesh
wire grid, coated with dielectric and mounted just
behind the screen. A pattern of +ve charge is
deposited on the grid & this pattern is transferred to
phosphors by continuous flood of electrons issuing
from the flood.

4. Just behind the storage mesh a second grid,
Collector, whose main purpose is to smooth out the
flow of flood electron. Electon pass thru. Collector at
a low Velocity & attach to +vely charged portion of
mesh ,but rest are repelled. Others pass thru. Mesh &
strikes the phosphor. The flood electrons are still
continue to move slowly. In order to increase the
energy of these relatively slow moving electron &
thus create a bright picture, the screen is maintained
at a high +ve potential.

5. Advantage:
 Very complex pictures can be displayed at
a very high resolution without flicker,
because no refreshing is needed.
 It is an inexpensive device.
Disadvantage:
 Ordinarily they do not display colors.
 Some selected part of a picture could not
be erased.

6. Flat-Panel Displays
Refers to a class of video devices that have
reduced volume, weight and power required
compared to a CRT. Currently used in TV
monitors, Calculators, pocket video games,
laptop computers & advertisement boards etc.
Two categories of Flat-panel displays are:
1.) Emissive Displays
2.) Nonemissive Displays.

7. Emissive Displays: are devices that convert
electrical energy into light. Examples are
Plasma panels, thin-film electroluminescent
displays and Light-emitting diodes(LED).
Nonemissive Displays: Use optical effects to
convert sunlight or light from some other
source into graphics patterns. Example is
Light-crystal device(LCD).