A projector is a device that integrates a light source, optics system, electronics and display(s) for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. There are hundereds of products available in the market and they are differentiated by their resolution, performance and features.

Display
There are several different display types with different picture quality and lens life; LCD, DLP and CRT are the most common.

• Cathode Ray Tube (CRT): CRT projectors deliver a high degree of illumination and can project high-resolution video and data at up to workstation frequencies. Computer resolution can be as high as 2,000 lines. The disadvantageof CRT projectors is that they need to be realigned for different types and brands of computer, so if you bring your laptop to the lecture theatre it may not match any of the pre-programmed options and a technician will need to be called to set it up.
  
• Digital Light Processing (DLP): The commercial name for this technology from Texas Instruments (TI): The technology inside is often referred to as either "micro-mirrors", or DMD: It works this way: build a few hundred thousand tiny mirrors, and line them up in 800 rows of 600 mirrors each. Now attach a hinge to each of those 480,000 mirrors. Attach each of those 480,000 hinges to its own very tiny motor! Power each motor with electrostatic energy! The motors tilt their mirrors up to 20 degrees at incredible speeds. This allows the mirrors to modulate light from a lamp, and send the "modulated signal" out through a lens, on to a screen. The most amazing part of DLP micro mirrors, is the scale of size. The 480,000 mirrors (actually 580,000 are used), hinges and motors are packed onto a "wafer" a bit larger than your thumbnail.
  
• Liquid Crystal Display (LCD): LCD stands for liquid crystal display and comes in many forms, sizes, and resolutions. Its primary purpose is to present a digital image for viewing. A common use of LCDs is as a display on a notebook computer. Polysilicon TFT LCD is a popular LCD technology for the top of the line LCD projectors. Monochrome Polysilicon LCDs are typically placed in each of the three color light paths inside a projector, one each for Red, Green, and Blue. This results in increased color saturation, with contrast ratios above 200:1. Polysilicon technology is also a bit faster than the Active Matrix TFT, for smooth video and multimedia.

Brightness
Projectors come in a wide range of light output. All other things being equal, the brighter the projector, the more it costs. When it comes to "optimum brightness" the rule is simple: get the brightest projector you can afford.

Brightness is measured in ANSI (American National Standards Institute) lumens: the brighter the projector, the higher the ANSI lumen rating.

In today’s market, projectors can be grouped by ANSI lumen output as follows:

• Less than 1000 lumens – these are the lowest light-output projectors available today, and they are typically the least expensive. If you are on a tight budget, there are a number of products in this category that may be perfect for your needs. Keep in mind that the low light output means that you will want to make your presentations in a dark or dimly lit room so that the image on the screen is not washed out by ambient room light.

• 1000 to 2000 lumens – this lumen range is a step up in performance and price. There are many SVGA and XGA products in this class to choose from. These machines are suitable for normal business conference room and classroom use. Presentations should be done with the room lighting reduced somewhat for best screen viewing, although a totally dark or dimly lit room is usually not necessary.

• 2000 to 3000 lumens – this represents the high-performance range of the portable and semi-portable projectors. Products in this class are suitable for large conference rooms and classrooms. They offer more flexibility in terms of ambient room light, since the image is bright enough that a reasonable amount of room light can be tolerated without washing out the image. They also offer more flexibility in terms of audience size since they can illuminate a larger screen without much loss of image quality.

• 3000 lumens and up – the ultra-bright projectors are in several performance classes unto themselves, ranging from 3000 up to 12000 lumens or more. Prices of these products also cover a wide range depending on other performance characteristics. They are used in a variety of large venue applications, including board rooms, conference rooms, training rooms, auditoriums, churches, concerts, nightclubs, and so forth.

Resolution
The sharpness and clarity of the picture on the screen is determined by a projector's resolution. Resolution refers to the sharpness of the image projected, as expressed in pixels (the higher, the better). When it comes to projectors however, the thing you want to pay attention to is the "Native Resolution." This refers to the true resolution (i.e. non-compressed, non-expanded) of the projector. Ultimately, you want a projector that matches the resolution of your computer exactly; if an exact match is not available, then choose the level that is slightly higher than the resolution of your system. (If you plan on using the projector with many different computers, then you want a projector with a native resolution that is as high as the highest resolution of all the units). Most projectors today support resolutions that are higher than their native resolution by compressing the number of pixels. However, much of the quality and detail of the projected image is lost when this happens. Do not be misguided by the maximum resolution capability of the projector; instead, just focus on what the native (true) resolution is. Resolution of projectors is differentiated in four categories. - VGA (640x480)
- SVGA (800x600)
- XGA (1024x768)
- SXGA (1280x1024)
- UXGA (1600x1200)
SVGA, or "800 x 600" – This is a popular resolution today, because most notebook computers are SVGA. Matching the projector resolution with the computer resolution will produce the best results. XGA, or "1,024 x 768" - XGA projectors are generally more expensive, and are the second most popular resolution format. Many of the newest products are coming out in XGA. They are getting more popular as prices drop and the use of XGA notebook computers increases. SXGA, or "1,280 x 1,024" – SXGA products are high resolution, and notably more expensive than XGA. These products are targeted for high end personal computer users and low end workstation users. They are used primarily for command and control, engineering and CAD/CAM applications where acute resolution of small details is important. UXGA, or "1,600 x 1,200" – UXGA is for very high resolution workstation applications that are detail or information intensive. These are expensive projectors that support a broad range of computer equipment. Relatively few products on the market have this native resolution.

Aspect ratio
The most popular aspect ratio is 4:3 (4 by 3). Early television and computer video formats are in a 4:3 aspect ratio, which means that the width of the image is 4/3 times the height. Examples: A 15 inch monitor is 12 inches wide by 9 inches high (9 x 4/3 = 12). A resolution of 640x480 is a 4:3 format (480 x 4/3 = 640). Other formats are 5:4 used by the 1280x1024 SXGA resolution, 16:9 is used by HDTV, and 3:2 for 35mm slides.

It is important to think about weight of projector as it might effect you if you are carrying your projector too much, so it is good to have a projector with a weight in a range of 2 to 3kg.

Ease of use
Most of today's projectors are very easy to use. They come with about as much hardware as a laptop. Usually just two to three cords (power, PS II mouse, USB, and audio/video cables) and the projector itself will pack into a bag small enough to carry on the plane, or place in the back seat.

They are plug-and-play, user-friendly and they can be set-up in a matter of minutes. Even with the challenges of a constantly changing environment, in most cases all you will need is a power outlet

Intangibles
Today, the technology has greatly improved. Projector manufacturers have added things that can make your presenting life easier and more successful. Some examples are; memory cards for computer-less presentation, digital keystone correction for versatility in projector placement, digital zoom and digital freeze for visual poignancy, wireless mouse control, on-screen pointer, multiple computer inputs for complex presentations, and wireless/wired LAN options. You may not require all of these bells and whistles for your purposes, but keep them in mind when shopping for a data projector.