7 Questions Concerning the use of a Data/Video Projector
- 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.
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 shinning 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 less 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.
- 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 computers 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, however for laptop LCD screens 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 will the planned projector handle your new computer's display resolution. Most new computers today are 1024x768 (XGA) display resolution. Laptops are 1280x800 (WXGA). Some higher performance computers are using 1920x1200 (WUXGA) 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.
- 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 (less 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.
- What size projector do I need?
This depends on the application. Is it a fixed installation, is it on a cart, or is it carried from location to location? If you are traveling a lot, it should be small and light weight. If, the projector is typically stationary or ceiling mounted, size doesn't matter much. The lightest projectors on the market today are less than 5lbs. You will appreciate the smaller size if you are racing between terminals at a major airport. You sacrifice features as you go down in weight, the light level is lower and you may lose auto zoom and focus, additional computer inputs, keystone correction, picture in picture, and image quality.
If, the projector is stationary or ceiling mounted, size doesn't matter much. The larger projectors will typically have more feature, a better image, and will run quieter. Another consideration for the fixed projector is the mounting location and the necessary image size.
The image size depends on the distance from the screen to the projector and the projector lens. The distance from the projector to the screen is called the "throw distance". As this distance increases the image gets larger. In many cases the projector is most conveniently located at some location like the rear of the room or some ceiling mount location. For such cases, a stipulated image size is obtained by selecting a projector that will provide the correct image size at the necessary throw distance.
One alternative is to use a projector that has the lens replaced to provide a longer throw distance. If you are at the back of an auditorium, the throw could be 50 feet or more. The amount of light, number of lumens, remains the same provided the image size has not changed.
For most projectors the throw length and related image size is usually found in a table or graph. Having a zoom lens let's you change the image size over some range. The situation is similar to cameras where fixed and zoom lenses exist. You have more flexibility with the zoom lens, but may pay slightly more.
- Should I use LCD, DLPTM, or D-ILATM technology?
Each technology has its own advantages and price is one of them. LCD projectors will typically give you better color saturation, have a lower noise level, and offer slightly better video. DLPTM will typically offer more lumens in a smaller sized projector, and have an image that has less space between the pixels. D-ILATM offers the highest resolution, film like quality, and highest contrast ratios with the truest colors when a Xenon lamp is used. The D-ILA will also be a more expensive projector. To really get a good idea of which projector will work best for you, ask a audio/visual dealer to show you the projectors side by side with the same image so you can evaluate the differences.
- Do you know what kind of warranty comes with the projector?
Get the best warranty you can find. Today warranties range from one to five years for parts and labor. Also, inquire about a free loaner program availability if something should happen to your projector within the first two years of operation. Many manufacturers offer this program to help their customers if their projector needs service.
- Who will service your projector if it is out of warranty?
ake sure that the dealer you purchased the projector from can either service the projector or send you to someone who can. This again is dependent on your projector being fixed or portable.
For a portable unit, it can simply be returned to the company that provided it, by normal shipping. Look in the user's manual and contact the manufacturer. This puts you in touch with the people that know the most about the projector.
For a fixed installation you may want the installer or some service organization to handle the situation without removal of the unit if possible. This is generally the case for most projectors. Remember that the projector has moving parts such as fans and will require periodic service depending on the level of use. It may be just a filter cleaning, but it is important to the continued operation.
Choosing a projector isn't as confusing as it may seem. Use these seven steps to help make the best decision for your application.
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