Joined
·
2,243 Posts
There is always an interest in gain when it comes to screens. I have recently seen many discussions and questions about gain. Some statements are valid, some are conjecture, but there does seem to be a lot of confusion about screen gain and the various ways it is achieved. More importantly there seems to be some questions about the pros and cons of gain and how it is achieved.
First a brief bit of history about the ‘Silver Screen’.
At the turn of the century, 1909 to be specific, motion pictures were becoming the rage. One problem that plagued the fledgling theater industry was that projectors and screen materials at that time were extremely limited and crude by today’s standards. This resulted in images being very dim and quite hard to see, but the public was still fascinated with moving pictures.
Adele DeBerri owned a theater in Chicago during this era. She was a unique individual, remember this was an era when women typically did not own and operate a business. Not only was she a pioneer in that respect, but she was an innovator as well. Adele had the idea to paint the screen image area with a silver paint that was highly reflective and therefore would reflect more light back at the viewing audience. That’s how the ‘Silver Screen’ was born. What many may not be aware of is Adele went on to developed a silver painted canvas projection screen that quickly became the standard for the industry. Da-Lite Screen Company, Inc. is the successor to the business founded in Chicago in 1909 by Adele DeBerri.
The reason for high gain screens date back to the earlier example of turn of the century projectors that needed something to focus the light and make the image brighter. Today projectors are much more sophisticated and ten fold better than the old ‘moving picture’ projectors back at the turn of the century. The projectors currently available are so bright that if a person was to look directly into the lens it could cause permanent eye damage. So if our newer projectors are significantly brighter than even projectors made ten years ago let alone turn of the century technology, and gain is to produce a brighter image- why do people still seek a high gain screen? Situation and setting is often the main reason. Excessively large screens also come to mind.
Why does “higher gain” make a screen appear better? Or does it? And how is “gain” achieved?
First, 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.
[BANANA]If a surface exhibits Lambertian reflectance, light projected on it is scattered such that the apparent brightness of the surface to an observer is the same regardless of the observer's angle of view. More technically, the surface luminance is the same regardless of angle of view.[/BANANA]
Like the saying, “Nothing in life is free” and a screen cannot create light. Gain is not the creation of light, it is the focusing and redirecting the diffused light back at the viewer. The price of this increased brightness is field of view, or viewing cone. The center of the screen and on axis viewing in the ‘sweet spot’ looks great, but anyone sitting off to the side will see a darker, sometimes even unwatchable image. So to increase the gain, or image brightness on axis, the light has to come from somewhere. Since a screen cannot create light, the off axis light is refocused back at the viewer.
Too much gain has other negative effects too. 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.
Gain in front projector screen materials is made by adding “mirror-like” materials that will reflect light back at the projector instead of diffusing the reflected light in a Lambertian distribution.
In the beginning it was silver, then came glass beaded products. In 1954, the first pearlescent materials were introduced. Pearlescents were innovative because they were clear and sparkly instead of silver. (That’s right, pearlescents aren’t something new or revolutionary)
Pearlescents work by the process of interference. The first interference pigments were obtained and produced by Nature. 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 much like what a prism does when it refracts light. 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.
Man made 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 allows light to pass through instead of acting like a normal pigment when it is used in paint.
Here is the problem: each layer reflects a small percentage at the front face of the particle, most of the light is transmitted (passed through the mica flake) and refracted. When light hits the back surface of the particle, a small percentage is again reflected and most continues on through. If the particles get stacked one upon another, the number of light reflections gets to be quite large. The resulting sparkle can look bright and somewhat impressive. If the concentration of flakes isn’t dense enough, then the screen can look ‘sparkly’ when hit with high powered projector light. The down side is color shift and light separation.
There is a newer solution and way around this prism effect and to increase gain without introducing color shifting other than 1954 technology and methods, and that is by the use of non-interference pigments. Instead of being based on mica, the key particle is aluminum oxide. It is thick enough so that it is opaque and will not allow light to pass through it as mica flakes (Pearlescent) do. 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. Also the prism effect is eliminated, which in turn eliminates or greatly reduces any color shifting.
Specular gain is gain that is not created from the base color. In other words, a bright white screen will have a higher natural gain than a darker gray screen. If a shiny surface coating is applied over the same two screens, the gain on the white screen would be higher than the gray screen since the base itself is adding to the overall gain. The base gray also adds to the overall gain, but at a lower ratio, therefore it will have a higher specular gain.
This can be confusing, and people may say “But how can a screen with lower gain hot-spot when a higher gain screen with the same surface doesn’t?” As explained this is due to the surface sheen of the coating on the gray contributing more to the gain than the base.
So even though the surface coating is the same for both materials, it makes up a high percentage of the overall specular gain for Fashion Grey than it does with Designer White. With more of the gain being from the coating, the specularity has increased, and that can increase the possibility of hot spotting.
Hopefully this shed some 'light' on a few things and this thread is intended to discuss some of the confusing aspects about screens, color, and light.
First a brief bit of history about the ‘Silver Screen’.
At the turn of the century, 1909 to be specific, motion pictures were becoming the rage. One problem that plagued the fledgling theater industry was that projectors and screen materials at that time were extremely limited and crude by today’s standards. This resulted in images being very dim and quite hard to see, but the public was still fascinated with moving pictures.
Adele DeBerri owned a theater in Chicago during this era. She was a unique individual, remember this was an era when women typically did not own and operate a business. Not only was she a pioneer in that respect, but she was an innovator as well. Adele had the idea to paint the screen image area with a silver paint that was highly reflective and therefore would reflect more light back at the viewing audience. That’s how the ‘Silver Screen’ was born. What many may not be aware of is Adele went on to developed a silver painted canvas projection screen that quickly became the standard for the industry. Da-Lite Screen Company, Inc. is the successor to the business founded in Chicago in 1909 by Adele DeBerri.
The reason for high gain screens date back to the earlier example of turn of the century projectors that needed something to focus the light and make the image brighter. Today projectors are much more sophisticated and ten fold better than the old ‘moving picture’ projectors back at the turn of the century. The projectors currently available are so bright that if a person was to look directly into the lens it could cause permanent eye damage. So if our newer projectors are significantly brighter than even projectors made ten years ago let alone turn of the century technology, and gain is to produce a brighter image- why do people still seek a high gain screen? Situation and setting is often the main reason. Excessively large screens also come to mind.
Why does “higher gain” make a screen appear better? Or does it? And how is “gain” achieved?
First, 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.
[img]http://i96.photobucket.com/albums/l190/wbassett/HTS%20Data%20and%20Charts/Diffuse_reflection.png[/img]
[BANANA]If a surface exhibits Lambertian reflectance, light projected on it is scattered such that the apparent brightness of the surface to an observer is the same regardless of the observer's angle of view. More technically, the surface luminance is the same regardless of angle of view.[/BANANA]
Like the saying, “Nothing in life is free” and a screen cannot create light. Gain is not the creation of light, it is the focusing and redirecting the diffused light back at the viewer. The price of this increased brightness is field of view, or viewing cone. The center of the screen and on axis viewing in the ‘sweet spot’ looks great, but anyone sitting off to the side will see a darker, sometimes even unwatchable image. So to increase the gain, or image brightness on axis, the light has to come from somewhere. Since a screen cannot create light, the off axis light is refocused back at the viewer.
Too much gain has other negative effects too. 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.
Gain in front projector screen materials is made by adding “mirror-like” materials that will reflect light back at the projector instead of diffusing the reflected light in a Lambertian distribution.
In the beginning it was silver, then came glass beaded products. In 1954, the first pearlescent materials were introduced. Pearlescents were innovative because they were clear and sparkly instead of silver. (That’s right, pearlescents aren’t something new or revolutionary)
Pearlescents work by the process of interference. The first interference pigments were obtained and produced by Nature. 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 much like what a prism does when it refracts light. 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.
Man made 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 allows light to pass through instead of acting like a normal pigment when it is used in paint.
Here is the problem: each layer reflects a small percentage at the front face of the particle, most of the light is transmitted (passed through the mica flake) and refracted. When light hits the back surface of the particle, a small percentage is again reflected and most continues on through. If the particles get stacked one upon another, the number of light reflections gets to be quite large. The resulting sparkle can look bright and somewhat impressive. If the concentration of flakes isn’t dense enough, then the screen can look ‘sparkly’ when hit with high powered projector light. The down side is color shift and light separation.
There is a newer solution and way around this prism effect and to increase gain without introducing color shifting other than 1954 technology and methods, and that is by the use of non-interference pigments. Instead of being based on mica, the key particle is aluminum oxide. It is thick enough so that it is opaque and will not allow light to pass through it as mica flakes (Pearlescent) do. 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. Also the prism effect is eliminated, which in turn eliminates or greatly reduces any color shifting.
[img]http://i96.photobucket.com/albums/l190/wbassett/HTS%20Data%20and%20Charts/hotspotting.jpg[/img]
Surface sheen is another way to quickly increase the gain, but it also raises the specular gain which almost always results in hot spotting. The higher the projector’s Lumen output, the more noticeable the hot spotting becomes.Specular gain is gain that is not created from the base color. In other words, a bright white screen will have a higher natural gain than a darker gray screen. If a shiny surface coating is applied over the same two screens, the gain on the white screen would be higher than the gray screen since the base itself is adding to the overall gain. The base gray also adds to the overall gain, but at a lower ratio, therefore it will have a higher specular gain.
This can be confusing, and people may say “But how can a screen with lower gain hot-spot when a higher gain screen with the same surface doesn’t?” As explained this is due to the surface sheen of the coating on the gray contributing more to the gain than the base.
Here are some graphs from when this was discussed about the laminate screens that hopefully will make more sense:
![]()
![]()
The pie charts as a whole represent the total gain. With the same surface coating for each, what changes is the ratio's of the specularity to the surface color and the basic gain of the color. If the coating remains the same, and the color gain decreases, then the ratio of specularity goes up even though the coating hasn't changed or added extra sheen.
So even though the surface coating is the same for both materials, it makes up a high percentage of the overall specular gain for Fashion Grey than it does with Designer White. With more of the gain being from the coating, the specularity has increased, and that can increase the possibility of hot spotting.
Hopefully this shed some 'light' on a few things and this thread is intended to discuss some of the confusing aspects about screens, color, and light.
