Many people are unaware of the differences between front and rear video projection. In nearly every case, rear projection will provide a brighter image not affected by ambient light for about half the cost of front projection.

In front projection, both the projector and people viewing the image are on the same side of the screen. The screen reflects the projected image and this is what the viewers see. The image brightness is determined by the ANSI Lumens (brightness) of the projector and the screen gain. Screen gain defines at what angles the screen is reflective to light. The higher the screen gain, the narrower the viewing angle will be (high gain screens can’t be used effectively in rooms with wide seating layouts unless multiple screens are used). Front projection screens reflect light – all light. The screen will reflect the light from the projector, but also ambient light in the room including light from windows, architectural lighting and theatrical lighting spilling onto the screen or directly aimed at the screen. This means both the perceived brightness and contrast of the projected image will be degraded when there is ambient light cast on the screen. Unless you’re in a totally darkened room, it’s nearly impossible to totally eliminate the effects of ambient light on a front projection screen. Higher ANSI Lumen projectors or multiple stacked projectors can be used to provide the brightness required, but this can come at a significant cost, one which many are unwilling to invest in. Many designers/installers prefer to use front projection because they are most familiar with these systems (and can make a lot of money putting them in).

In rear projection, the screen is an opaque material. The projector is on one side and those viewing the image are on the opposite side. The projector transmits the image when it is cast onto the screen material. In much the same way, ambient light (on the viewing side of the screen) will be cast on the screen and transmitted through it as well. Remember that in front projection, both the ambient light and the projected image light are reflected equally. In rear projection, the projected image light is traveling one direction (toward the viewer) while the ambient light is traveling the opposite direction (to the area behind the screen (projection room) which is painted black and thus absorbs the unwanted light.

Rear projection provides a couple key benefits over front projection. First, the viewers are looking directly at the projected image, not a reflection of it. This image can be nearly twice the brightness as a front projection screen using the same projector. Second, ambient light becomes much less of an issue and because of this, a rear-projected image has a much higher contrast level and the image will appear brighter. No one will see the projector since it’s in a room behind the screen and noise from the projector is greatly reduced since the projector is in a separate room. If the room is constructed properly, access to the projector for regular maintenance (filter cleaning, bulb replacement) is much easier than having to pull out a ladder.

Although existing facilities are typically limited to front projection solutions, there is rarely an excuse for any church in new construction to not use rear projection. Ambient light issues are removed from the equation, lower-brightness projectors can be used (to achieve the same perceived image brightness compared to front projection), and projector noise is removed from the sanctuary. This all results in an image that is brighter and has higher contrast, there is no concern for ambient light (unless you aim a light directly at the screen), and very little, if any noise. Oh, and by the way – rear projection costs nearly half as much as front projection (for equal image brightness).

We’ll discuss the types of screens and image brightness in a future blog entry.