The Fundamentals of Display Technologies 1585looking at the LCD light path illustration, Figs. 44-3, we
begin with a metal halide lamp for illumination. The
lamp approximates pure white light from which the
colors of the spectrum can be extrapolated. Color
(RGB) is achieved by incorporating dichroic mirrors or
filters into the light path. The dichroic mirrors filter out
all of the unwanted color spectrum and pass on a narrow
band of color coordinates of red, green, and blue,
permitting each of those colors in a pure form to be
transferred to the main optical prism or combiner just
behind the projection lens.
LCD projectors come in various sizes, shapes, light
outputs, and resolutions.
Typical native resolutions for commercial LCD
projectors are 800 × 600, 1024 × 768, and 1280 × 1024.
In terms of weight, the brighter the projector, the
bigger the lamp housing requirement and hence the
heavier the projector.
Modern LCD projectors vary in size from 5 lbs to
over 50 pounds for the high-brightness models.
Brightness has long been the holy grail of projectors
and LCD with flat panel brightness reaching 1500 cd/m²
and projector brightness achieving 15K lumens.
44.8.3 Digital Light Processing
Digital light processing was developed by Dr. Larry
Hornbeck of Texas Instruments and brought to market
in the mid-1990s. It is fundamentally a digital light
switch that is used in projection applications as far
reaching as tiny pico projectors to be inserted in cell
phones all the way to digital cinema projectors replac-
ing 35 mm film in movie theaters. Its compact size
along with single chip and three chip variations make it
unique in the world of display technologies, Fig. 44-4.44.8.3.1 DLP Characteristics- Projection technology, no fixed screen size.
- Single or three chip configurations.
- 16:9 and 16:10 aspect ratio panels.
- No radiation or high-voltage emissions.
- Low power consumption.
- High resolution, up to 2 K.
- High brightness and contrast.
- Does not require polarized light.
44.8.3.2 DLP Operates in the Following Manner- DLP™ is based on an optical semiconductor called a
digital micromirror device, or DMD. - The DMD is an extremely precise light switch that
enables light to be modulated digitally via millions of
microscopic mirrors arranged in a rectangular array. - Each mirror is spaced less than 1 micron apart.
- These mirrors are literally capable of switching on
and off thousands of times per second and are used to
direct light toward, and away from, a dedicated pixel
space. - When the display is off, all of the mirrors are flat.
Figure 44-3. LCD projection TV optical path.