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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 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 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. 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’t matter much. The larger projectors
will typically have more features and a better image. 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, DLP™, or D-ILA™ 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. DLP™ will typically offer more lumens
in a smaller sized projector, and have an image that has less space between
the pixels. D-ILA™ 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?
Make 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.
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