Visual Communication Systems- Part II

In Uncategorizedby tfwm

Last issue, (March, 2000) we discussed the importance of planning for the implementation of a proper projection system for your church.

Now let’s talk about some of the components that make a visual communication system. We will begin by looking at projectors. As mentioned last issue, we are seeing overhead projectors give way to the newer technology of LCD, DLP and ILA projectors. The progression to these newer technologies has been a very rapid one. LCD panels allowed the overhead projectors to be used for more than still images created by light passing through a prepared transparency. They could now be used to display computer and video images in real time. From there the manufacturers began to combine the light source, lens and the LCD into one unit and called it an LCD projector.

DLP (Digital Light Processing) was developed by Texas Instruments and has become very common in multimedia projectors. ILA is a combination of two technologies: the traditional CRT (cathode ray tube) and LCD to create what is called a light valve projector. The LCD projector seems to be the most common among those used in churches.

These units are becoming smaller and brighter all of the time. The light output of a projector is measured in ANSI lumens. Lumens are the measure of light, and ANSI (American National Standards Institute) is the organization that governs the system of measurement. Just a few years ago a projector that had a rating of 300 ANSI lumens was considered very bright. Now it is not uncommon to see projectors with 2000+ lumens being used in churches. They are even some using projectors with 3000+ lumens.

These are not high maintenance machines. Most require only the lamp and the ozone filter to be changed. The lamps can last from 750 to 8000 hours of use. Many are made to be mounted either in the upright or inverted position and can reverse their images for rear projection applications. These units typically have at least one computer input and one video (NTSC) input. Many offer multiple computer and video inputs. Most have zoom lenses that allow for flexibility in the placement of the units.

Choosing A Projector

This is a matter of matching the needs of your application with the capabilities of the projector. In many cases the main issue is brightness. One may ask, “How bright is bright enough?” That is a difficult question to answer, especially if there is more than one person trying to answer it.

The best place to begin is establishing a point of reference by looking at foot- lamberts. When a projector’s brightness is measured in ANSI lumens, a fixed image size is assumed. A projector that has a rating of 500 ANSI lumens will look great in a conference room where the image is approximately 60 inches diagonal. That same unit will look quite dim when trying to produce an image that is three times that size in a very well lit church. Measuring the foot-lamberts of a particular display can help clarify things a great deal. Foot-lamberts are determined by taking the lumens and dividing them by screen area.


ANSI lumens = 1500
Screen size = 9′ x 12′
9’x12’=108 square feet
1500 divided by 108 = 13.89 foot-lamberts

(A typical foot-lamberts rating for a television is 30; for a home theatre it is 8; and for a movie theatre it is 14)

The Screen

This brings us to our next component: the screen. Screen gain also affects foot-lamberts. When a screen is said to have a gain of one, it is neither adding to nor taking away from image brightness. As gain increases so does the foot-lamberts rating.


Foot-lamberts = 13.89
Gain = 1.8
13.89 x 1.8 = 25 foot-lamberts

Can you see how important screen gain can be? There is a catch though.

There are many different types of screens: front projection, rear projection, motorized, fixed mounted, portable, optical, diffusion, etc. Some churches choose front projection because it is not as costly as rear-projection. Some choose to mount a motorized screen above the baptismal directly to the back of the main platform. The screen can be lowered when needed and raised when after use. Others choose to have a permanently mounted screen(s) while others choose to use portable screens. Choosing the right type of screen is a process of matching the characteristics of the screen to the needs of your application, while keeping in mind the budget limitations.

Front projection screens are made with different surface types for specific applications. The variations in the designs usually balance two opposing concerns: screen gain and viewing angle. This is where the “catch” comes in. As screen gain increases, the viewing angle typically decreases. The screen acts as a reflection device for whatever light hits it. A screen can be designed in such a way that it concentrates that light in one direction resulting in increased screen gain.

If the need is to provide a greater dispersion of the light resulting in a wider viewing angle, then gain typically suffers. An easy way to understand this is to think of light as paint. The larger area needing painting the thinner the coat of paint will become. In the same way the larger the area of light dispersion, the less intense it will be. This concept holds true for front projection screens as well as rear projection screens.

Rear projection screens can be manufactured from a glass, a form of Plexiglas or a flexible material. These materials are prepared as translucent surfaces that disperse the light from the projector to create the image.

The two most common types of rear projection screens used in fixed installations are optical and diffusion screens. Optical screens are the equivalent to a large group of tiny lenses put together to create the screen surface. This type of screen has very high gain while at the same time maintains a very wide horizontal-viewing angle.

The down side is that optical screens are quite costly and offer very little vertical-viewing angle. These screens are not uncommon among consumer-grade projection televisions and actually work quite well in that environment. The reason is that a television does not normally need much of a vertical-viewing angle because it is usually at eye level with the viewers. This is not generally the case with church display systems and this makes the diffusion screen a better fit for many of these applications. With diffusion screens, the viewing angle remains constant in the horizontal and vertical viewing plains.

One issue to be aware of when considering rear projection screens is screen non-uniformity (also referred to as mottling). For screens that exceed approximately six feet in either width or height, mottling is quite common.

Mottling shows up as wavy lines in the screen material that are more apparent with dimmer light. There are tolerance levels established by each manufacturer for what amount of mottling is acceptable. Because the manufacturing processes are kept confidential by each manufacturer, it is difficult to determine why mottling occurs.

One way to minimize the effects of mottling in overall image quality is to increase the light from the projector. In one church, mottling was most apparent as the camera was panning across a white wall. The mottling appeared as irregular-vertical streaks that remained stationary as the actual image content moved across the screen. In this case our recommendation was to darken the walls that were appeared behind the pastor when the camera was focused on him.

Keep in mind, mottling is not terribly apparent to the casual observer or even to the more technical observer and should not keep you from choosing this type of screen. It is an issue to be aware of and should be a topic of conversation with the screen manufacturer you choose.

Source Components

We’ve talked about the two most common and fundamental components of a visual communication system: the projectors and screens. Let’s talk briefly about the source components for these systems.

The most common are computer and video. (either live or recorded) The main application for a system is to provide a great view of the service from any seat in the house. The system may also be used for song lyrics and to view prerecorded video material played back from Beta tape. You may also use a satellite system to pipe in other broadcasts as desired.

Some churches use visual presenters (also referred to as document cameras) in place of overhead projectors. A visual presenter contains a camera that captures an image of a document or an object and sends that image to an external display device. This allows a presenter to share printed material or hand written notes with the congregation.

When integrating these components into a system it is sometimes necessary to amplify the source signal if the source and the display are placed far apart from one another. Typically a computer signal does not carry nearly as far as a video signal and therefore is more often the source in need of amplification. Either line amplifiers or distribution amplifiers handle the amplification. The choice of amplifier depends once again on the application. One common choice is to install a distribution amplifier that receives a VGA signal from a computer CPU and sends the signal to the local monitor, and an amplified signal to the large-screen display.

Many projectors can receive these multiple sources and be selected by using the source selection on the projectors. A simple way to handle this is to hard wire the projector’s remote control and place it near the sources. Third party remote panels can be used as a cleaner surface-mounted solution. A common choice is to route the sources through a separate switcher at the location of the sources and feed a single signal out to the display.

In some cases the video signal is fed through a device called a line-doubler or scan-converter that converts the computer signal into a television video signal. That signal is then fed through a video switcher complete with fade controls. This allows for fades from computer text (e.g. scripture references) to the view of the person ministering.

These systems can serve congregations quite well but it is always important to remember that the function is to serve. A system should never be designed to “steal the show” rather to augment the communication process.

Careful planning, proper needs assessment and wise product selection will yield the best system for your church. Our hope is that this information will give you a good idea of what to look for when considering this type of technology for your church. Don’t be afraid to ask for advice. Expert advice can help you avoid many unnecessary headaches and help make your experience in this sometimes complex industry a pleasant one. Enjoy the journey!