Selecting a Projector

A Liquid Crystal Display is made up of a thin panel that contains pixel elements that act as light valves, letting more or less light pass through each pixel. Color displays use Red, Green, and Blue (RGB) sub-pixels to produce almost any color (or shade of grey) at each pixel. This system matches the way our eyes work, as the cones on our retinas sense red, green, and blue primary colors, and our brain determines every other color that we see by weighing the relative strength of the red, green, and blue light.

LCD projectors send a bright white light to dichroic mirrors coated with a thin film that separates the white light into red, green, and blue light. Each primary color is sent through a small LCD imager panel. These LCD imagers typically have HD (1920x1080) or WUXGA (1920x1200) resolution.

Rather than using a white light source, some projectors use a blue laser, which is aimed at a spinning wheel coated with a phosphor that is stimulated to produce yellow light. The yellow light is then converted to red and green light by dichroic mirrors. Some of the blue laser light is directed to the blue LCD imaging panel, while the red and green light is directed the red and green LCD imaging panels.

While there are some true 4K (3840x2160 or 4096x2160) projectors, less expensive 4K projectors achieve an apparent 4K resolution through “pixel shifting.” Two-phase pixel shifting displays one picture at one position for half of the video frame, and a second picture at a diagonally shifted position for the other half of the video frame. This happens faster than the human visual system can detect, and the effect is to have one higher-resolution picture. Some projectors use imagers with a native resolution of 2716x1528 in order to produce a similar number of pixels (8,300,096) overall to true 4K (8,294,400).

Liquid Crystal on Silicon (LCoS) is a type of LCD. It is a reflective active-matrix LCD microdisplay that uses a liquid crystal layer on top of a silicon backplane. The red, green, and blue light sources are transmitted through the LCD, reflected off the silicon backplane, and then combined and focused to create the projected image.

LCoS projectors have better contrast and darker black levels than the other digital projection technologies.

The newest and most popular projector technology is Digital Light Projection (DLP). Like the other technologies, red, green, and blue light is sent to separate imaging panels. DLP imagers utilize an array of microscopic mirrors to control the light for each pixel in the image. Each micromirror can pivot into an “on” position, where it reflects light in the direction of the focus system (and to the screen), or an “off” position, where light will be reflected in a different direction. To change the brightness of each pixel, the micromirror is modulated at a high frequency, spending more or less time in the “on” position.