What are Digital Projectors?

Brendan McGuigan

Digital projectors are the modern replacement to more traditional transparency projectors. Transparency projectors work by shining light through a semi-transparent material, such as slides or film. Digital ones, by contrast, project a digital image directly from a computer through a lens on to a screen. There are four technologies which may be used in these types of projectors.

Digital projectors are high quality items.
Digital projectors are high quality items.

Eidophor projectors, used in the 1950s, were the first digital projectors. They used an oily surface in a rotating disk with light shining through it and employed an electron beam to disrupt the oil in a very precise manner. Although Eidophor projectors were a very primitive form of projector, they were nonetheless capable of producing color images. In the wake of much simpler, cheaper, and higher-fidelity devices, however, Eidophor projectors are no longer used.

Digital projectors bypass the need for physical photo slides.
Digital projectors bypass the need for physical photo slides.

Cathode Ray Tube (CRT) digital projectors operate along the same general principles as a CRT television set. There are three main configurations for CRT projectors: the projector may have one RGB (red, green and blue) color tube with a single lens, one black-and-white tube with a rotating color wheel, or three RGB color tubes with three lenses. In all of these configurations, an image is produced at a relatively small size ranging from six to twelve inches (15-30 cm), and then magnified with a lens onto a large screen. These devices are quite bulky and heavy, making them suitable primarily for fixed locations.

Liquid Crystal Display (LCD) digital projectors are much lighter and more portable than their CRT cousins, making them widely popular. With the advent of new LCD technologies, digital projectors have been developed which have very clear and crisp fidelity even at large projection sizes. The LCDs used in these machines are approximately the size of a small color slide, and in fact the projectors operate very much like a traditional slide projector. The main difference is that the slide is constantly changing.

Both CRT and LCD projectors are known as transmittive projectors, meaning that light shines through the image to project it. There is another class of digital projectors, however, known as reflective projectors, which provide a much higher quality of image.

Texas Instruments produces the chip for the only currently viable reflective digital projector using a technology known as DLP (Digital Light Processing). These have an array of tiny mirrors, one for each pixel. As these mirrors reposition themselves to either place light on the screen or not, they produce shading which creates the illusion of a complete image. DLP technology is used in theatres as they make the transition to digital projectors, due to its extremely high quality and fidelity and its lack of pixilation even at high image sizes.

Digital projectors can be used with traditional screens.
Digital projectors can be used with traditional screens.

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Discussion Comments


When setting up a digital projector at home, choosing a great backdrop is important for the quality of your picture. While you can just use a white wall, professional screens offer beautiful quality, though they can be quite pricey.

I would recommend making your own screen for your digital projector. All you need is some 53 inch white seamless paper, the kind that photographers use for backdrops, some wood for your frame as well as brackets, and lastly some velveteen fabric to cover the frame.

Make the frame first, then lay the white paper on the back and staple it in place. Voila! You have a cheap and easy to make projection screen.


Getting a digital projector for your home can really make movie nights a lot more impressive. There are new versions coming out that are getting more affordable, and while some would argue that traditional large screen TVs are the way to go, I think having a digital projector is a unique way to show movies at home.

There are a lot of these coming out that now offer HDMI ports and 3D technology. For those who love gaming, you could potentially hook up your system to a projector and play your game on a truly huge display.

I think people should give a digital projector a try, but as a word of caution, you get what you pay for.

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