How Projectors work
This video explains how DLP and LCD projectors work:
How DLP Projectors Work
DLP projectors rely primarily on a DLP chip, or digital micromirror device (DMD), which comprises up to two million tiny mirrors, each mirror one-fifth the width of a human hair. Each of these mirrors can independently move toward or away from a light source to create a dark or light pixel. The color is fed to the DMD by a beam of light from a light lamp source, which then passes through a spinning color wheel before it reaches the chip, and the image is fed through the lens and onto the projection screen.
The conception diagram of a color wheel used in DLP.
A DLP projector with three-chip architecture can deliver up to 35 trillion colors. A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is routed to its own DLP chip, then recombined and routed out through the lens. Three-chip systems are in higher-end home theater and large venue projectors, and DLP Cinema projection systems in digital movie theaters.
How does an LCD projector work?
LCD projectors use 3 LCD technology systems with the same LCD displays as those used to create images in watches and other electronic devices. This system combines three liquid crystal displays, where an image is created in a multi-step process. A light source provides a beam of white light, which is passed to three mirrors (or dichroic mirrors) specially shaped to reflect only a certain wavelength of light.
Here the mirrors reflect red, blue, and green wavelengths. Each colored light beam is fed to an LCD panel, which receives an electrical signal. The signal instructs the panel how to arrange the pixels in the display to create the image. The same image is created by the three LCD panels, but each with different hues due to the colored light through the panel. The images then combine in a prism, resulting in a single image with up to 16.7 million colors. Finally, the image is passed through the lens for projection onto a screen.
Technology and Light Source
DLP technology is 'reflective'. Instead of passing a light source through a LC material, light is reflected off the DMDs. In a single-chip DLP projector, light from the lamp enters a reverse-fisheye, passes through a spinning color wheel, crosses underneath the main lens, and reflects off a front-surfaced mirror, where it is spread onto the DMD. From there, light either enters the lens or is reflected off the top cover down into a light-sink to absorb unneeded light.
LCD projectors use transmissive LCD, which allows light to pass through the liquid crystal. In LCD projectors there are always three LCD panels, and they are always light transmissive devices rather than reflective or direct view displays
Being light-source agnostic, DLP technology can effectively use a variety of light sources. Typically, the main DLP light source is a replaceable high-pressure xenon arc lamp unit. Alternatively, ultra-small or pico DLP projectors use high-power LEDs or lasers. For LCD projectors, Metal-halide lamps are used given their outputting an ideal color temperature and a broad spectrum of color. Smaller metal-halide lamps make LCD projectors smaller, hence more portable than most other projection systems.