Digital Projectors Demystified - Tech Learning

Digital Projectors Demystified

from Technology & Learning You know you want them. But how do you go about buying them? Digital projectors are becoming a common sight in U.S. schools. Small wonder: A projector can serve many roles, from letting teachers give tours of educational Web sites to having students present their projects to the entire
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from Technology & Learning

You know you want them. But how do you go about buying them?

Digital projectors are becoming a common sight in U.S. schools. Small wonder: A projector can serve many roles, from letting teachers give tours of educational Web sites to having students present their projects to the entire class.


The BenQ MP611/611c DLP projector is designed to run quietly.

With this trend comes questions: Which projection technology is the most cost-effective? Which requires the least maintenance? How can I get the best price over the lifetime of this product? To help answers those and other questions, T&L has compiled this list of essential considerations.

1. What are my options?

There are two types of digital projectors currently available today. The first uses Texas Instruments' DLP (digital light processing) technology, while the second employs LCDs (liquid crystal display) and lamps.

In a DLP projector, the actual image is controlled by a chip called a DMD (digital micromirror device). It is literally loaded with millions of microscopic, independently tilting mirrors, each one being responsible for one pixel of the final image. The amount of tilt on each mirror controls the amount of lamp-generated light reflected through the projector's lens, thus controlling the grayscale (white to black) level of each specific pixel. Each pixel's actual color is controlled by a rapidly spinning color wheel, which the light travels through before hitting the micromirrors. Put this altogether, and you have the DLP projection system, which is being used in DLP high-definition televisions and video projectors. The brightness of a given DLP device is based on the power of the light source being used.

In an LCD projector, a small clear-screened LCD is used to create the image. Then bright light is projected through this screen and an enlarging lens to display it on a portable or fixed wall screen.

Which display option you choose very much depends on personal preference: It's a matter of seeing DLP and LCD projection systems operating side-by-side and making up your own mind.

But what about the cost? "Both digital projection options are roughly the same price-wise," says Jeffrey Macdonald, display analyst with TFCinfo, an Austin, Texas-based consulting firm that specializes in audio/visual market research.

2. How bright should the projected image be?

"The brighter the image delivered by a digital projector, the less you have to darken the room by dimming the lights and drawing the curtains," says Doug McIntosh, an educational technology resource teacher with the San Diego Unified School District. "In today's schools, teachers want to be able to use digital projectors without having to do either of these things. That's something we kept in mind when putting out an RFP for LCD digital projectors. So the key is to decide how bright an image you require, then buy the digital projector that meets this specification. If you buy more than you need, you'll pay more than you have to. But if you buy less, students and teachers will suffer eye strain from a dimly lit image," he says.

When it comes to projectors in general, brightness is measured in ANSI (American National Standards Institute) lumens. When it comes to digital projectors, 1600 to 2000 lumens is considered to be sufficient brightness to deliver clear images in a normally lit room. (If the room is prone to direct sunlight, you may want to buy extra lumens.)

"You can buy a 2000 ANSI lumens SVGA LCD projector for under $700 if you buy in volume," says McIntosh. "Thankfully, as the second largest school district in California, we were able to get excellent volume pricing [from Epson]. We even got three-year factory service warranties with that."

3. Should I pay extra to get maximum resolution?

Both DLP and LCD digital projectors commonly come in two resolution levels: SVGA and XGA. SVGA resolution delivers an image measuring 800-by-600 pixels, while XGA produces a more detailed image measuring 1024-by-768 pixels. According to Macdonald, a typical 1600-2000 ANSI lumens SVGA projector costs between $600 and $700 when bought in bulk, while a similar XGA model costs $900 or more.

"In most cases, SVGA resolution is more than adequate," Macdonald says. "The only real reason to go to XGA resolution is if you intend to project very large images in big rooms and are concerned about image sharpness. But in most classrooms, SVGA is more than good enough."


The Barco iD R600 + DLP series can be used in bright classrooms.

4. Can my digital projector multitask?

Definitely! A digital projector can display it all: computer graphics; video from DVD, tape, or TV; and feeds from any kind of connectable digital camera-based equipment (such as document cameras).

"About four to five years ago, we declared the television set to be 'dead' in our schools," says McIntosh. "Given how much LCD projectors have dropped in price, and their ability to support document cameras, computer outputs, and television signals, it makes sense to use them to multitask within our schools."

5. What about lamp life?

Hint: If you want to reduce your replacement expenses—digital projector lamp bulbs can cost $200 or more each—reduce your operating power. For instance, once you've bought a 2000 ANSI lumens projector, try running it at 1500 ANSI lumens (most projectors offer a low-light setting). Doing so will substantially increase bulb life, says Macdonald. Of course, if you are running the projector in a brightly lit room, this may not be an option.


The LCD Hitachi CP-X253's 2000 lumens should deliver enough brightness under normal light conditions.

6. Portable or built in?

Because today's digital projectors are typically the size of a telephone directory, they're easy to store away between uses; you can also carry them from classroom to classroom. But this portability also makes digital projectors hard for theives to resist--and easy for them to steal. You may want to play it safe and mount the projector out of reach on the ceiling. Mounting also allows you to hardwire the projector to in-classroom computers, document cameras, and video sources. Some projectors include theft-prevention features, such as the ability to send an automatic e-mail or text-message alert to IT directors when removed from their mount.

Whether you choose DLP or LCD models, digital projectors have dropped sufficiently in price to become affordable to most school districts. Generally, they last six to seven years (with lamp bulb replacements), require very little physical space, and can perform multiple functions in the classroom.

James Careless is a freelance journalist based in Ottawa, Canada.

Buyer's Checklist

  • Start by determining what kind of environment your digital projectors will be used in. Will the images have to be bright enough to be seen in full-room lighting? Are there windows that will allow in sunlight as well? Or will they be used in dimmed surroundings?
  • A rule of thumb: In most cases, a digital projector that provides 1600-2000 lumens of light will be sufficient for normally lit rooms.
  • Once you know what kind of lighting conditions the digital projectors will be operating in, the next choice is resolution. The economical SVGA is good enough, but XGA is best when the images need to be blown up to serve large rooms and when the images must be extremely detailed.
  • Should your digital projector be portable or built-in? If it is portable, the unit can be shared between rooms. However, portable projectors are light and small enough to be easily stolen. If theft is an issue in your schools, consider permanently mounting your digital projector in a specific classroom.
  • Save money by having digital projectors serve multiple purposes. These can include acting as large-format computer displays, TV monitors, and document camera displays.
  • Extend bulb life by operating digital projectors at their lower light settings where possible.
  • Both DLP and LCD digital projectors provide comparable image quality at comparable prices. Decide for yourself which is best by having one of each made available for side-by-side testing.

Digital Projector Resources

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