Adele DeBerri owned a movie theatre in Chicago at the turn of the 20th century. Projectors and projector screen materials were quite limited and so the resulting image was not particularly bright. She had the idea to paint the image area with a silver paint that was very reflective and therefore would “throw” the light back to the audience. That’s how the “silver screen” was born. With that, projection screen manufacturing became a new industry.
Today, most projectors would scorch a person’s retina if they looked into the lens. So why are videophiles looking for a “high gain” projector screen material? Quite simply, they desire the depth and quality of image that cannot be obtained using wall paint. There is lots of debate and discussion regarding this very subject. Image quality is constantly a subject. Why does “higher gain” make a screen appear better? Or does it? And how is “gain” achieved? Let’s try to answer these questions….
Firstly, gain is the ratio of brightness of your projection screen material to a white standard such as barium sulfate or magnesium carbonate. These materials are used by the industry to set a flat white “Lambertian” light distribution where every point in the audience would see the same image brightness. A gain of 1 represents a screen as bright as magnesium carbonate. A gain of 1.1 means it is 10% brighter and a gain of 2 means a screen is twice as bright. What price do you pay for a high gain projector screen? Quite simply: field of view – those sitting off to the side away from the center of the screen see a darker image. Remember the “sweet spot” from the old projection TV’s? You wanted to be directly in front of the screen; otherwise, you saw a very dark image. Those front projection screens actually “focused” the light to create a bright screen but at the cost of field of view. Even today you can see this effect in many models of rear projection big screen TV’s. Too much gain has other negative effects. Those viewing the image directly in front of the projector screen may have to endure a movie that is uncomfortably bright. And then there is the effect called “hot spotting” where the image literally shows a bright circle in the center of the image. The newer models have solved some problems using LCD’s and plasmas. Uniformity of those new screens is outstanding. Never the less, they still have to obey the laws of Physics and they still remain confined in size. Even the largest ones are small compared to the image of a front projection screen and at a very steep price.
Gain in front projector screen materials is made by adding “mirror-like” materials that will reflect light back at the projector instead of scattering the reflected light in a Lambertian distribution. Once, it was silver, then came glass beaded products. In 1954, the first pearlescent materials were introduced and patented. Pearlescents were innovative because they were clear and sparkly instead of silver and “with profile”.
Pearlescents work by the process of interference. Nature was the first to make interference pigments. Mother of pearl is an excellent example. Some seashells also have the interference effect. Interference is the separation of white light into its component colors. By making a series of thin layers that are clear and refract light, an interference pattern is set up. Sparkle and shimmer are two ways to describe pearlescence.
Manmade pearlescents are made from the mineral mica. The mica is processed into small particles and then coated with a very thin layer of titanium dioxide. The layer is so thin that it actually transmits light instead of acting like a normal pigment when it is used in paint.
Figure 1 graphically shows the problem: each layer reflects a small percentage at the front face of the particle, most of the light is transmitted and refracted. When light hits the back surface of the particle, a small percentage is again reflected and most is transmitted. If the particles get stacked one upon another, the number of light reflections gets to be quite large. The resulting sparkle looks impressive. The down side is, color shift and light separation. This looks great on cars, but not projection screens.
The newest innovation in the pearlescent world is; “non-interference pigments”. Instead of being based on mica, the core of the particle is aluminum oxide. It is thick enough to not transmit light. It is then coated with the same thin layer of titanium dioxide that the interference pigment was but the optical results are MUCH different. The reflections are reduced and the degree of color separation is minimized. This is the foundation of patent-pending DIY front projection screen paint available exclusively from DIY Theatre.
So what is so special about this non-interference pigment?
Let’s play a numbers game for a minute. Suppose you have a 700 lumen projector. Twenty years ago, this was a state of the art projector. Say your projector screen is sized that 10 foot candle hit the screen. The pearlescent screen will reflect 4% of the light that hits the front surface and transmit the rest onward. Four percent is not much, just 0.4 ft-lambert reflected. This is hardly noticeable. But on the same size screen, if a 2000 lumen projector is used, the light on the screen is now almost 3 times, so that 4% reflection is now over a foot-lambert. That reflection is more easily detectable, especially since it is color shifted typically, red shifted. So noticeable, that it will become a distraction. That’s for one mica particle. Well, there are a couple hundred thousand of those mica particles laying on that screen.
This distraction is virtually eliminated in the DIY Theatre White Platinum projection screen which is DIY projector screen paint. Actually it is not paint but rather a patented polymer coating that is applied like paint. DIY Theatre is the only manufacturer of projection screens that has formulated a non-interference pigment for their “pearlesent” product. You may visit www.diytheatre.com to gain further understanding of why this product is unique.
Now, it is possible to have a “gain screen” and avoid the unwanted color shift. With a DIY Screen kit, you can choose the contrast you desire to match your projector performance, image size and your ambient conditions. We were awarded a US Patent for the non-interference pigment technology we have introduced for digital and high definition projection. It is this technology that sets us apart from all other screens available on the market including the most expensive traditional screen fabrics. Follow this link for a complete description and graphic of this pigment performance: DIY Theatre Screen Performance The White Platinum screen is fully mixed to a pre-determined gain and contrast. We are proud to note that our screen was recently listed in an Electronic House magazine feature article “2012 Products of the Year”.
There are several advantages to our “paintable” screen. The most important is that we do feel strongly, as stated above, that our optical pigments are superior to those used in traditional fabric or vinyl screens. This also gives you full control over the height and size of the image – no custom sizes needed. We recommend that you mount your projector and then adjust the height and size until you find what looks perfect for your theater. Then you install our screen – no measuring required. Our screen will not wrinkle and the edges will not curl in – it will always be flat on your wall. All this and it is less expensive. Our product is water based and very consumer friendly. There are no solvents or that typical chemical and ammonia smell of regular paint.
Whether you choose a DIY kit or some other material, DIY Theatre hopes you consider these fundamental options to optimize your theater experience. Remember that screen gain does not have to interfere with or compromise your home theater.
Richard Burrows, Ph.D. has over 12 years of experience dedicated to research and development of projection screen materials. As a Doctor of Chemistry he has immersed himself in the field of optics and how new technologies can improve front projection screen performance. Dr. Burrows currently consults with several companies including DIY Theatre, LLC which can be found at www.diytheatre.com and Dr. Burrows can be reached through email@example.com DIY Theatre is a manufacturer of diy projection screen materials. They offer a line of front projection screen paints that feature full control over the final projection screen size at a substantial cost savings over traditional projection screens. DIY projector screens paints can be ordered direct on-line at DIY Theatre Products and Pricing with no need for exact screen or image measurements.