Display Technologies

Display Technologies

1. Video Displays

   • Flat-panel: modern personal computers
   • Projector: found in boardrooms and classrooms
     • rearview: self enclosed and shoots image onto screen from rear
     • frontview: shoots image from front and requires screen at proper distance
     • LCD projectors are light and inexpensive
     • DLP (digital light processing) uses single processor and array of tiny mirrors to project front-view inage
       • softer image than LCD
   • Virtual reality headsets: gamers and explorers
     • creates immersive experience by mounting two high-resolution screens into a headset that blocks external visual sensory input
     • uses OLED to power tiny high resolution stereo panels
       • no backlight required
       • thin and energy efficient
       • better contrast than LCD panels

2. LDC Monitors: liquid crystal displays on todays computing devices

   • takes advantage of property polarization
     • translucent sheet above sub-pixels are red, green, or blue
       • each forms a physical pixel
   • composed of specifically formulated liquid
   • full of long thin crystals that orient themselves in the same direction
   • early screens used matrix wires for charge; y wires, vertical; x wires, horizontal
     • gives blurred effect
   • TFT (thin film transistor) or active matrix tech used in current LCD monitors
     • provides faster picture display, definition and tighter color control
   • common LCD panel technology:
     • TN (twisted nematic)
       • fast but only adequate color
     • IPS (in-plane switching)
       • great color
     • VA (vertical alignment)
       • display is in between TN and IPS
   • LCD components
     • backlights illuminate image
     • moderns use light-emitting diode (LED) for backlights
     • typically uses edge LED backlighting (top and bottom)
     • direct LED backlighting puts bank of LEDs behind panel
       • expensive and used more electricity
     • early LCDs used cold cathode fluorescent lamp (CCFL) technology
       • low power, even brightness, long life
       • each CCFL backlight needs inverter
   • backlighting
     • reflective: mirror behind panel bounces ambient light back to user
       • cheap, power efficient, but difficult to read without ambient light
     • transmissive: backlight behind panel shines toward user making display readable in low-light situations
       • must have powerful backlights
     • transflective: uses both backlight and partially reflective layer between backlight and the LCD display to capture ambient light
       • more expensive

3. OLED (organic light emitting diode) flat panel screen that uses an organic substance as semiconductor material in LEDs

   • uses series of thin light emitting films
   • when electric current is applied, photons move through substance to emit bight light

4. Plasma: flat panel screen uses small cells filled w/ noble gases and phosphors to create color

   • electric current applied to gas ionizes it into a charged plasma
   • each cell illuminates a pixel
   • used for large tv's 1990s-early 2000s
     • mostly replaced by LCDs

5. CRT (cathode ray tube) contains large vacuum tube with flat end covered in phosphors

   • emitter shoots a stream of electrons at phosphors to create image
   • bulky and expensive
   • displaced by flat panel technologies, only in old computers today

6. refresh rate: how often a screen can change completely

   • standard is 60Hz
     • higer-end is 144, 165, and 240HZ

7. contrast ratio: difference between lightest and darkest spots

   • dynamic contrast ratio measures difference between full on, all white screen, and full off, all black screen

8. color depth: 24 bit, 16.7 million colors

9. lumen: amount of light provided by light source

10. throw: size of image at certain distance

11. lamps: gets hot, expensive