The Hidden Facts Behind Projection Screen Technology
Projection screens are some of the most overlooked items in visual display systems. While screens are usually the first and possibly the only thing you see, they are typically the last thing you think of when installing a system. But there is more to a screen than just a flat surface. Screens have multiple variables and specifications to consider before installation to make sure you are achieving the best possible image for your viewers. The key goal of a visual display system is communicating to all your viewers in a clear and possibly entertaining way so that your message is remembered.
Screen Gain, Viewing Cone, Screen Material Types, Aspect Ratio, Resolution, Contrast, and Uniformity are some of the technical specifications of the screen. Other variables such as type of projector, ambient light, and viewer seating also play a large part in installing the correct screen, not to mention style. This may seem like a lot to integrate, but a few insights on the above terms might be of help to make a better decision when installing your system.
Lets start with the basics. Projection screens come in a variety of fixed and retractable frame styles, along with a variety of material types. Choosing the correct frame and material is important in order to achieve optimal viewing.
When purchasing a screen, choosing the correct material is imperative. Screen material can be manufactured in 2 ways. One is from one complete sheet and the other is from 2 sheets seamed together. Seamless screens are always better, for a seam will always be visible. Seamless screen material can be manufactured 60 feet by 90 feet.
Gain is the industry term used to measure the amount of light reflecting from a screen surface. No actual light “gain” takes place. Gain measures the screen brightness and directional characteristics.
Imagine you are looking at a projection screen directly in front of you (you are perpendicular to the center of the screen). You will be viewing the screen at 0 Degrees, referred to as Peak Gain at Zero Degrees Viewing Axis. Peak Gain at Zero Degrees Viewing Axis is where the screen’s peak brightness occurs.
Viewing at an 80 Degree angle would mean that you were looking at the screen from its side. At an 80 Degree angle, light loss is at its peak.
Screen Half Gain
Half Gain is the standard used to measure the brightness performance of a projection screen when the viewer is observing the screen from an extreme angle or “off to the side”. A projection screen’s peak brightness occurs when the viewer is perpendicular to the center of the screen. This is referred to as Peak Gain at Zero Degrees Viewing Axis. As the viewer moves out to the side, away from the center of the screen axis, the brightness of the projected image will deteriorate. When the brightness drop off reaches 50% of the peak gain, that determines the screen’s half gain (or half brightness).
Example: Let’s say a projection screen has a peak gain of 4 and its output is 22 Foot Lamberts when directly in front of the screen at zero axis. Let’s say the screen’s half gain specification is at 52 Degrees.
That means when a viewer is seated at 52 Degrees off the center axis of the screen, the viewer would observe half the brightness as the viewer who is seated directly in front of the screen – 11 Foot Lamberts – Gain of 2.
So what does this gain have to do with anything? Well, you need to find a screen with the right amount of gain in order to have everyone in your audience able to see what is projected on the screen. Not only does the image need to be bright enough for everyone in the last row to see, but the image must also be bright enough for everyone in your viewing cone.
Screens have a radius in which your audience can see the image without being too dark; this is your viewing cone. You do not usually want people outside your viewing cone.
The viewing cone and screen gain work very closely to one another. The higher the gain the smaller the viewing cone and the brighter the image. Now the bright the image does not necessary mean it’s a better image. If you have a matte white screen with a 1.35 gain and have a very bright projection, your image will be too bright (but this is also dependent on the size of the screen, how far the projector is, and ambient light).
Covering the basics of screen gain and viewing cones may create more questions than answers. This is a great step! For now you know screens do make a difference.