Choosing a projector isn't as confusing as it may seem. Use these seven steps to help make the best decision for your application.

1. What are lumens and why are they important?

The lumen is a measure of the amount of light. It indicates the total amount of light leaving the projector or falling on the screen. The brighter the image the more lumens are measured.

To measure lumens, a meter is used that measures the light falling at one spot on the screen. The light level, at a number of locations on the screen is measured and an average is determined. The average light shining on the screen and the size of the image on the screen determine how much total light is striking the screen. This total light is stated in lumens.

The larger the image you want to project, the more the light is spread out. As the image gets larger it appears less bright, since there are fewer lumens in a given area on the screen.

For example, if 2000 lumens is used to form a 4 by 5 foot image (the image has 4x5=20 square feet) this results in 100 lumens in each square foot area. The value is found by 2000/20=100. If the image size is doubled to 8 by 10 ft., then the screen area is increased four times (8x10= 80 square feet). The lumens are now spread across an area that is 4 times larger. Consequently, the number of lumens present at each square foot must be reduced by 4, resulting in 25 lumens per square foot. This means the light level or brightness of the image will be reduced by 4 times.

For image visibility, the light from the projector must exceed the background light that is naturally falling on the screen. Look at the screen without the image present and it usually appears white. This is due to the ambient room light. To become visible the projected image must have sufficient light to exceed the background light. Thus each installation has to deal with the particular conditions that exist for that screen and the normal light.

In general the more lumens produced by the projector, the brighter the screen image appears. Knowing the amount of lumens available from a projector permits predicting the image visibility and best size.

2. What is the native resolution of the computer I am using?

You need to know this because you will want to purchase a data/video projector that will handle your computer's current output. Native resolution is the normal resolution of the CRT monitor or laptop LCD screen. Generally for monitors, there are a number of possible settings. For laptop LCD screens, however, their inherent resolution is defined by the number of pixels making up the screen. You can find the current resolution by looking at the "display settings" of the PC.

You may want to think ahead about what your next computer will be and determine if the planned projector will handle your new computer's display resolution. Most new computers today are 1024x768 (XGA) display resolution. Laptops are 800x600 (SVGA) or 1024x768 (XGA). Some higher performance computers are using 1280x1024 (SXGA) resolution.

Projectors today will handle their native resolution and usually also compress the next higher level resolution. Compression uses a software program to determine the best way to display a higher resolution. Today's compression methods are so effective that it is difficult to tell the image has been compressed.

3. How many lumens do I need to adequately address my typical audience?

This depends on the ability to control the location ambient lighting as well as the required image size. If you are presenting to a small audience (fewer than 5 people) in a relatively small room, and lights can be dimmed, you may only need a projector that produces 500 lumens. If the room size increases and lights cannot be dimmed, you may need a projector that produces 2200 lumens or more.

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