Pro Production: The Essentials Of Display Technology

Display Technology. There are a few different types of display technologies used in projectors with the most common two being LCD and DLP.

LCD or Liquid Cristal Display projectors split the light-source beam into three separate colors, and these separate colored beams then pass through LCD panels that open or close pixels and let the light pass. A combiner mounted before the lens joins all three colors together and the full color image passes through the lens.

DLP or Digital Light Processing is based around an optical unit called a Digital Micromirror Device. This DMD is a semiconductor covered with tiny mirrors, each representing pixels, which reflect the light beam into the lens, or away from the lens into a heat sink. A segmented color wheel is spun in front of the beam which provides the ability to get a full color image. A newer version of this technology is called Three Chip. It uses a prism to split the light beam into colors and then projects each color onto its own DMD.

Other display technologies include Liquid Crystal On Silicon (LCOS) that use reflective liquid crystal panels, Light Emitting Diode (LED) technology that is finding its way into smaller projectors, and Cathode Ray Tubes (CRT) that are still preferred by some for home theater applications but are no longer in widespread use in A/V.

Lamp Technology. Halogen and metal-halide lamps are the most common, but newer projector technologies can employ lasers or LED bulbs for illumination.

While you can certainly project an image on any surface, a projection screen is normally used. Screens are categorized by their use in front or rear projection, design and size. Front projection screens require that the projector be located on the audience side and their opaque surfaces are designed to reflect the projector light back to the audience.

Screens that focus the light more toward the center and less to the sides are said to have a higher “gain” than others. High-gain screens may be beneficial in areas where the ambient light is higher and the audience is seated directly in front of the screens, but these types have limited use in A/V.

Rear screen systems use a translucent fabric for the surface, and the projector is located behind the screen. There are also dual screens that can accept both front and rear projection.

Screens for A/V come in two main designs, screens that roll up for storage inside a base, and screens that are assembled into a frame that the surface (called the fabric) attaches to.

Many roll-up screens have a leg system built in and are often referred to as tripod screens. Skirting drape is often used to conceal the legs from view during use, and provide a more finished look. Roll-up screen can only be used for front projection because of their design, as they have one or more support structures directly behind the screen.