Last Update October 24, 1996
Types of Projection Systems:
- Liquid Crystal Display (LCD) panels. These come in various
resolutions and are either active or passive matrix. They sit on
top of an overhead projector. The units are quite portable and can
easily be carried to class.
- All in one projection systems: These are a projector plus LCD
panel into a built in unit. Until recently, these units were a bit
bulky and heavy and were not be convenient for personal transport to a
classroom. Now there are some models which weight about 20 lbs and
are more easily transportable. These are called LCD projectors
or sometimes multimedia or data projectors.
- Ceiling Mounted RGB systems. These are permanent fixtures that
have a control panel at the front of the room. In general, this is
not a good solution. AT the very least, these units should be
mounted only in rooms with fairly high ceilings so that you have
a reasonable chance at getting the beam angle correct so that you
don't have convergence problems. However, with the new flexibility
of today's portable LCD projectors, its not clear to me that ceiling
mounted units should even be considered anymore.
Mininum Requirements for decent projection in a classroom:
- A good overhead projector - should be rated at least 4000
lumens but 6000 would be better. A wide angle lens is often necessary
as most classroom don't have enough back focal distance to give
you a sufficiently large image. The new metal halide overhead porjetors
are now rated at 11,000 lumens.
- Good control of lighting. Any ambient light that makes it to the
display surface has a significant effect on the visibility. The best
room light situation is one where the front of the room is dark. Leaking
light from windows is an extreme problem in this regard making many
current classrooms on campus unsuitable. The optimal situation is one
in which the room lights in the back of the room can be lowered to
a point where there is still enough light for note taking.
Most of the LCD panels on the market, even with a good overhead,
still require fairly low light settings for visibility. The LCD
projectors are significantly brighter but still limited to resolutions
of 800x600 at the most (see more below).
In any case, minimizing stray light on the display surface itself is
- A white, rigid wall is an ideal projection surface. Most screens are
not ideal. The convergence properties of most LCD panels (convergence
means the letters appear black and are not surrounded by blue or red
faint outlines) are quite extreme. A screen is not a hard focal surface
and hence focal and convergence variations over the surface of the screen
can exist. A fairly rigid screen made of material with glass beads
mixed in represents the best projection surface, however, such screens
are fairly expensive. A little paint on a wall is an inexpensive
Color vs Monochrome: The only reason to ever get a monochrome is if the
only classroom application is projection of text and no images.
- Active vs Passive Matrix: The principal difference between
these two technologies is the refresh rate of the panel. Active matrix
refreshes at a rate of 30--60 times per second. Passive matrix refreshes
much more slowly causing two fundamental limitations:
1. You can not effectively play video or show animation through
a passive matrix panel - the individual frames will ghost or blur.
2. You can not keep track of movements of your pointing device (mouse)
on a passive matrix panel as you will move it faster than it can be
Of course, active matrix costs more then passive matrix (see costs section
- Resolution: This is key. Units come with either 640x480, 800x600,
1024x768 or 1280x1024 resolution. You pay for resolution at a rate
of about $2000 per incremental step. You need to seriously think about
the resolution requirements you will need. If your principle classroom
application will be to present web pages containing course material and
other useful information you will definitely want the 1024x768 resolution.
If your principle application is to run software on a PC or MAC and then
project it, then you can get by with a resolution that is the same as
that on your screen.
Until very recently, most LCD projectors were limited to 640x480 resolution
and could only do 800x600 in a compress and highly pixelated mode.
Now, there are two very good true 800x600 projectors that we have
evaluated (see below). The higher resolution units do not yet exist,
except for one 1280x1024 fixed focal length LCD projector made by
ASK. This has a list price of about $17,000.
- Whiteboard: Some panels have whiteboard capability which allow you
to draw directly on the screen that you are projecting on. This can be
useful at times.
- Monitor loopback cables. Many units offer cabling that allows a
monitor to be hooked up as well. This is very useful for the instructor
who can then look at the monitor instead of the wall. However, this
can also be detrimental to the presentation if the presentor merely
stars into the monitor.
- Video Input: The latest active matrix panels accept video/Svideo input.
Thus one can hook a VCR/laserdisc directly to the panel and play video through
- Remote control pointing features: Newer units offer the ability
to use the remote control as a mouse by providing an RS232 port on
the projector. However, this requires disabling the internal pointer
on your laptop, which is something difficult to do in Windows 95.
As an alternative, we recommend the use of a radio (not infrared)
controlled mouse such as the Track Man Live product form Logitech.
We have had excellent success with this unit and have been able to
communicate with the laptop, and hence the presentation, from a distance
of up to 30 feet (it depends on the ambient RF in the room).
- Focal Length: Since most LCD presentations by business or in
conference rooms this is not an issue. But its a big issue in large
classrooms. We are actively searching, without much vendor cooperartion
I might add, for a long focal length LCD projector that has a throw
distance of 50--80 feet so that we can locate these units in the projection
booth along with the slide projectors and 16mm film projectors. Buhl
optical makes some reducing optics that can be used but they are
expansive and they don't increase the focal length enough. Think of
it this way, you know when you go to the movies and before the start
of the movie there is a static slide show. Why not use an LCD projector
for some multimedia show - because units don't exist with the correct
optics to focus the image to fill a theater screen. There is a market
out there, are you listening vendors?
- Most units directly accept VGA or SVGA input and are hence
designed for use with a PC.
- Interfacing the unit with a MAC requires a special cable.
- If you want to use a unix platform then you should purchase an NCD
MCX or HMX X-terminal which has a video out that you take directly to
the LCD panel. Alternatively, some units, like the Proxima 920 will
take a direct connection from a Sparc 20 workstation.
- Some laptops have non-standard video drivers which are not recognized
by LCD panels. Futhermore, many laptops these days are hardware
configured to present 800x600 on the laptop screen. When using a
640x480 projector, it is not possible to have simultaneous display
on the laptop and the projector in most cases. Still other laptops
don't have the functionality to have simultaneous display in any
resolution. In most cases, however, the image on the wall is bright
enough to be used as a monitor. While this is not an endorsement,
we use the IBM Think Pad Model 760-ELD in classrooms here. We
also highly recommend the 3Com ethernet connector.
Important Limitations to be aware of
- The brightest projection systems are the all-in-one projector
plus LCD panel. However, currently all of these systems are limited to
resolutions no greater than 640x480. However, in summer of 96 it
is expected that the higher resolution LCD projectors will be available.
And indeed, there is a full 1280x1024 unit now on the market made by
ASK. However, this unit has fixed focal distance and maximum image
size of 12x12 feet. It is also very expensive at the moment (see prices
- Loop back monitors when used in conjuction with a MAC are tricky.
You must have a good multisync model. Some LCD panels actually use
the monitor itself to determine the sync rate. There can be instances
where you get a good image on the monitor and a very poor image on
the LCD panel itself. There are also instances where the MAC senses
the panel as a VGA monitor and the other monitor in the loop won't
work at all.
- Bulb life on high intensity overhead projectors is about 25 hours.
At the lower setting on these units its 100 hours. For the newer
LCD projects that use metal halide bulbs, their life time is 700 -
- Different colors display differently. In general greens, red and
black are the best but blue often doesn't have much constrast.
- There are two types of focus: real focus and convergence. Convergence
means the red, blue and green guns all hit the focal target at the
same place so that the letters appear black. Often times convergence
is a property of the exact location that the LCD sits on the overhead.
Moving the LCD panel an inch or so can make a big difference.
- The contrast controls on LCD panels have a wide range of functionality
and some are clumsy and redundant. In general, one has to fiddle for
a couple of minutes to get the best contrast.
- NEVER switch power supplies and cables- use only those that actually
come with the unit. The power requirements are different with each unit
and hence applying to much voltage can fry some components.
- NEVER drop heavy weights (like lead) on the glass surface - it
- Proxima: There equipment seems to be the best and they now
are on the leading edge with new technologies. Both the 920 and
846 models are excellent units.
- Sharp: Within the past year, Sharp has come up to Proxima standards
first with the QA 1750 and now the QA 1800 and the 2500 high-rez
panel. These are as good of units
as the Proxima. The one disadvantage is that Sharp continues to put
the power connection on the opposite side of the unit as the other
cable connections. This can be cumbersome. Sharp's new metal halide
projector, the Sharp 1000 has extremely good brightness (I believe
it has the highest ansi-lumen rating) and is ideal for fixed situations
(i.e. its not real portable). The Sharp XG-630 is a portable (20.5 lbs)
270 ansi lumen 640x480 LCD projector with double the scan lines for
video. It has fixed focal length and is the best value for the
money (see below). We highly recommend this unit for the K12
- In Focus: Also very good and have come out with new products, however,
they are no longer the industry leader as they were back in 1993-94.
- Canon: A new player that has made a few mistakes in basic ergonomic
design of some units.
- NEC: They make the best high-end stuff where high-end means
greater than $10,000
- Sanyo: Another new vendor that makes some excellent stuff. They
offer two new products that are worth consideration. The PLC-700M uses
a new technology (called TFT - thin film transistor) for more accurate
color reproduction. Its truly impressive but definitely not portable
as it ways about 50 lbs. The Sanyo 5500, however, is a 16 lb 500
ansi-lumen true 800x600 LCD projector. Its amazing but it costs
$7000 (educational discount as of Summer 1996 - price probably
- 3M: We really like their model 9700 overhead projector. Very
good design. The 9800 is quite bright but changing the bulbs is
a little more cumbersome. Recently, 3M has introduced what we consider
to be the best portable 640x480 projector. The model number is 8020
and its called a multimedia projector. We have done extensive side
by side comparisons between the 8020 and the LightPro 580 from In
Focus. 3M wins easily. This unit is sufficiently bright that it can
be used in mostly normal room light and has excellent video playback
capability. The 3M8020 is about to be updated to the 3M8030 which
offers ansi-lumens compared to
the 300 ansi-lumens of the 8020 (the human eye, however, won't
easily detect this 5/3 improvement in brightness). We have bought
a number of 8030's for use in 250 seat classrooms here and are
quite pleased with their performance (plus its real cool to take
a unit home on the weekend and watch football games on your living
3M has also come out with the model 8650 which is a true 800x600
unit which has 1000 ansi-lumens of brightness. This is a beautiful
projector if you can afford it. Educational price is $7500. We
are also a little wary of buying this resolution if the 1024x768's
aren't too far behind.
Update: Well the 1024x768 LCD projection market is still not here
as of Sept. 1997. In the mean time there are several impressive
800x600 UNITS out there including the 3M8640 but we definitely like
the SHARP XG-NV1U Notevision - extremely crisp display and nice
and portable. Highly recommended.
Although prices continue to vary and in general are coming down here
is a rough breakdown from the bottom up of the kind of pricing that
is available at the educational discount level.
- Black and White 640x480 --> $1000
- Passive Matrix Color 640x480 --> $1500 (these aren't really
being made anymore)
- Active Matrix 640x480 --> $3000
- All-in-one 640x480 Active Matrix LCD projector with fixed
focal distance --> $3200
- All-in-one 640x480 Active Matrix LCD projector with zoom
- 800x600 LCD Projectors with active matrix and zoom optics --> $5-6K
- High resolution 1024x768 Active Matrix Panel --> $7000
- High-resolution ceiling mounted Units --> $12-15,000
- High quality 4000 lumen overhead --> $500
- High quality 6000 lumen overhead --> $800
- High quality 8000-10000 lumen overhead using metal halide bulb -->$1500
- Extra MAC cable --> $90
Links to Projection Vendors and their Products
The Electronic Universe Project