Projection and Color
It takes several steps to create a picture in an LCoS television. The process includes a high-intensity lamp, a series of mirrors and microdevices arranged into a cube, a prism and a projection lens. From beginning to end, here's what happens:
- The lamp creates a beam of white light.
- The beam passes through a condenser lens that focuses and directs the light. It also passes through a filter that only allows visible light, which helps protect the other components.
- The white light is separated into red, green and blue light in one of two ways: The beam passes through a polarizing beam splitter (PBS), which divides the light into three beams, and those beams pass through filters that add red, green and blue. The beam passes through a series of dichroic mirrors that reflect some wavelengths while allowing the rest of the light to pass through. For example, the dichroic mirror can separate red light from the white light, leaving blue and green, and a second mirror can separate the green light, leaving only blue.
- The newly created beams of colored light simultaneously come into contact with one of three LCoS microdevices - one each for red, green and blue. We'll look at exactly what happens in the devices in the next section.
- The reflected light from the microdevices passes through a prism that combines the light.
- Prism directs the light - which now creates a full-color image - into a projection lens, which magnifies the image and displays it on the screen.
Most rear-projection LCoS televisions use this process. Some projectors use a linear setup rather than a cube, and the white light strikes surfaces that color it red, green and blue before reaching the microdevices. A very few systems use only one microdevice along with other methods for adding color. Some examples are color wheels like those found in DLP systems or transmissive dyes on the microdevices themselves. Some systems use additional polarizers or filters to further improve picture quality and contrast.
Without the projection lens, the picture created in this process would be too small to see clearly. That's why LCoS technology falls into the category of microdisplays -- displays that are too small to see without some kind of magnification.