Understanding Video Projector Specifications:
You may know that projector brightness is measured in ANSI Lumens, but do you know what the other specifications and what effect they have on performance? Here are the more common terms and their significance.
Picture Brightness is measured in ANSI lumens. When video projectors first started to become popular, the best you could get was around 200 – 250 lumens. A few years ago, a typical decent portable projector produced about 600 ANSI lumens. Now the smallest one worth considering for portable applications is around 3000 lumens. A more typical size for installation is around 4000 – 5500 lumens.
ANSI lumens is an international standard measurement which ensures apple to apple comparison when you are looking to purchase a product from different manufacturers. If you are using your projector on a small screen such as 6 x 8 foot, a 3000 lumen projector is usually the perfect choice. This will give you plenty of brightness for word projection, even with the lights on. For bigger projections you need higher brightness projectors.
Contrast Ratio refers to the difference between the brightest part of the image and the darkest. In other words, if the contrast ratio is 400:1, this means that if part of the image is at full brightness and another part is as dark as possible, the brightest part will be 400 times brighter than the darkest part.
Contrast Ratio works hand in hand with lumens. A projector with a 1000:1 contrast ratio will look brighter than one with 400:1, even though they have the same lumen rating. This is particularly true in a darkened room. Be very careful when you are comparing projectors. Picture Brightness in lumens doesn’t tell the whole story until you combine it with Contrast Ratio.
The minimum standard for electronic theatre is 300:1 contrast Ratio. The higher the Contrast Ratio, the better your movies and pictures will look. 1000:1 looks significantly sharper.
LCD Projectors use three glass Liquid Crystal Display panels (red, green and blue). Light shines through these panels, through the lens and onto the screen. Each panel is divided into a number of squares (pixels). Each pixel is individually controlled to allow the proper amount of light through. The quality of the projector panels determines the contrast ratio (full on / full off). The quality also determines the thickness of the black area between the squares. The thinner the lines and the higher the contrast ratio, the better the picture looks.
Resolution refers to the number of pixels on each panel. Since these projectors are primarily designed to project computer images, the resolution value follows computer resolution standards. The typical resolution you are likely to find is XGA. This is 1024 pixels wide by 768 pixels high. XGA projectors are quite acceptable for screen sizes up to about 9 or 12 feet, at a normal viewing distance, with a computer image.
When you use a screen larger than 9 x 12, the pixels become more noticeable. An SXGA projector has a resolution of 1400 pixels wide by 1050 high. This makes the dots less noticeable. XGA resolutions are quite common for portable projectors. There are some larger projectors with SXGA and UXGA resolution.
Although higher resolution looks better, because the image appears smoother with smaller dots, it has no affect at all on how well you can see the image. This is of course unless the words are so small that the lines are smaller than a couple of pixels. If this is the case however, they will probably be too small for most people to read anyway. What higher resolution does do, is make your pictures and words look sharper, and reduce the visibility of the dots.
As projector brightness increases, generally resolution also increases. This is partly because it is assumed that a brighter projector will be used on a larger screen and therefore the resolution will become more noticeable.
One thing to keep in mind is that although computers can take advantage of higher resolution, video sources such as DVD, VCR and most Cameras can’t. A video tape has a resolution of less than half that of a SVGA projector. Even high resolution cameras and DVDs don’t come up to XGA resolution. Blue Ray Discs do achieve this high resolution however.
This refers to the consistency of brightness over the entire image. For example, if a projector has a Uniformity of 90%, and it is projecting a pure white (or single colour) image on the entire screen there will be no more than 10% variation in intensity across the entire screen.
Better quality projectors have higher % of Uniformity, and therefore produce a more accurate image.
LCD Panel System:
This refers to the size, number and type of LCD panels the projector is using.
Number of Pixels:
This refers to the number of tiny squares which make up the projected image. The number is determined by the resolution and aspect ratio of the projector. For example, an XGA projector with an aspect ratio of 4:3 has 768,432 pixels per LCD panel making a total of 2,359,296 pixels.
Aspect ratio refers to the ratio of width to height of the projected image. Typical computer images are 4 units wide by 3 units high. This is also the ratio for standard television. Therefore for church applications, a 4:3 ratio is usually ideal. For home theatre on the other hand, the newer 16:9 ratio might be more desirable.
When choosing a projector, keep in mind that all projectors will handle all aspect ratios. The question is, which one will you usually be projecting. At this point in time, if it is primarily for computer projection, 4:3 is probably your best choice.
This refers to the minimum and maximum size image the projector is capable of projecting and still be in focus. It is not usually of concern when selecting projectors.
This is very similar to Image Size. It refers to the minimum and maximum distance within which the projector will focus.
This is tied to the Zoom Ratio. It tells you the minimum and maximum distance the projector can be from a given size screen. The minimum distance will be (screen width x smaller number) and the maximum distance will be (screen width x larger number). For example, a projector with a Throw ratio of 1.7 – 2.2 can fill a 10 foot screen when placed between 17 feet and 22 feet from the screen.
This specification refers to the different computer video resolutions the projector will accept. For example an XGA projector will probably accept VGA, SVGA, XGA and SXGA. Although its native resolution is XGA, it will process the other ones internally to provide the best image possible.
Rear Screen Projection:
This is a feature which reverses (mirror image) the projection so that it can be used for Rear Screen Projection. It is simply a function on the menu which you can turn On and Off.
Unlike Overhead Projectors which need to be positioned in the center of the screen to give a square image, Video Projectors are designed to be even with the bottom of the screen. When a projector is ceiling mounted, obviously you don’t want to locate it at the bottom of the screen, so we turn the projector upside down and position it at the top of the screen. In order for the projector to be Ceiling Mountable, it must invert the image (turn it upside down), so that we can mount the projector upside down.