Color Perception and Your TV

Color Perception,Transmissive Technologies

  • LCD – LCD pixels do not produce their own light. In order for an LCD TV to display an image on a TV screen, the pixels have to be “backlit”.
    What happens in this process is that the light traveling through the pixels is rapidly dimmed or brightened,
    depending on the requirements of the image.
    If the pixels are dimmed enough, very little light gets through, making the screen appear darker. Color is added as the light travels through the LCD chip and then through red, green, and blue color filters.
  • 3LCD – Used in video projection, works in a similar manner to LCD TV, but instead, chips scattered through an entire screen source,
    white light is passed through three LCD chips and a Prism and then projected onto a screen.

The Transmissive/Emissive Combination – LCD with Quantum Dots

For TV and video display application, a Quantum Dot is a man-made nanocrystal with special light-emitting properties ,
that can be used to enhance the brightness and color performance displayed in still and video images on an LCD screen.

Quantum Dots are nanoparticles with adjustable emissive properties that can absorb higher energy light of one color and emit lower light of another color (somewhat like phosphors on a Plasma TV),

but, in this case, when they are hit with photons from an outside light source
(in the case of an LCD TV with a Blue LED backlight), each quantum dot emits color of a specific wavelength, which is determined by its size.

Quantum Dots can be incorporated into an LCD TV in three ways:

  • Placed inside of thin glass tube (referred to as an Edge Optic) inside the TV’s light source structure between a blue LED edge light source and the Light Guide Plate
    (the structure that spreads the light across the screen area) for edge-lit LED/LCD TVs.
  • On a “film enhancement layer” placed between a Blue LED light source and the LCD chip and color filters (for Full Array or Direct-Lit LED/LCD TVs).
  • On a chip, where quantum dots are integrated directly on a blue LED for use in either edge or direct-lit configurations.

For each option, the Blue LED light hits the Quantum Dots, which are then excited so that they emit red and green light
(which is also combined with the Blue coming from the LED light source).

The colored light then passes through the LCD chips, color filters, and on to the screen for image display.

The added Quantum Dot emissive layer allows the LCD TV to display a more saturated and wider color gamut than LCD TVs without the added Quantum Dot layer.

Reflective Technologies

  • LCOS (also referred to as D-ILA and SXRD) LCOS is a variant of 3LCD and is used in video projection.
  • Instead of passing light through each of the three LCD chips and then through color filters and the lens,
    the LCD chip is on top of a reflective base,
  • so when a colored light source passes through the chip is automatically reflected back and sent through the lens to the projection screen.
  • DLP (3-Chip) – Used in Video Projectors – The key to DLP is the DMD (Digital Micro-mirror Device), in which every chip is made up of tiny tiltable mirrors.
  • This means that every pixel on a DMD chip is a reflective mirror. The video image is displayed on the DMD chip. The micromirrors on the chip (each micromirror represents one pixel) then tilt very rapidly as the image changes. This produces the grayscale foundation for the image.
    • In a 3-Chip DLP video projector, three light sources are used (or white light passed through three prisms).
    • The colored light is then reflective off of three DLP chips (they are all grayscale, but are each is receiving different colored light).
    • The degree of tilt of each micromirror in relation to the color light source at any given time determines the colors in the image. The reflected light is then passed through the projector’s lens to the screen.