Q: I keep seeing the word "gain" in projection screen descriptions. What does it mean and is it important?
A: To over-simplify it; the higher the gain the brighter the image on that screen.
A projector screen works by reflecting the light back from your projector to your audience's eyes.
The brightness of the image reflected back off of the screen's surface is measured in units of "gain", gauging the reflectivity of that surface.
The gain number represents a ratio of light that is reflected back from a surface from a light source. This ratio is in relation to the light reflecting off of a block of either barium
sulfate or magnesium carbonate, serving as the industry's standard for a gain of 1.0.
Gain is measured from the vantage point where the screen appears to be at it's brightest. This is generally the very center of the screen, directly in line with the projector. This is at 0° and known as the "Zero Degree Viewing Angle". As you move to either side of this position the brightness of the projected image may start to diminish. The point at which the brightness diminishes to 50% brightness from the measurement at the Zero Degree Viewing Angle is known as the "Half Gain Viewing Angle".
A viewer outside of this viewing angle (also known as viewing cone) will see the image at half the
brightness as the audience inside of the cone.
A screen with a gain measurement of greater than 1.0 infers that the image projected back off of the surface is brighter than the image being projected at the surface.
For example; a projector screen with a gain of 1.5 will project back the light 1.5x brighter than the light being projected at the screen. A 1,000 lumen projector aimed at a screen with 1.5 gain will be perceived at 1,500 lumens. The screen achieves this by focusing the light into a more narrow reflective angle, instead of uniformly reflecting the light in all directions. This is why higher gain screens have a smaller viewing angle.
A projector screen with a gain measurement of .8 will reflect back at 80% of the original brightness. That same 1,000 lumen projector will be viewed by the audience at only 800 lumens.
Some projection surfaces also have a "Vertical Half Gain Angle". These surfaces are generally
ambient light rejecting surfaces which require specific placement of the projector in order to achieve maximum brightness for the intended audience while diminishing the ambient light hitting the screen's surface. Draper's High Performance XS850E and Elite Screen's CineGrey5D are both angular reflective materials with vertical viewing cones in addition to the standard horizontal viewing cones.
Q: It sounds as though a high gain screen is better. When would I choose a lower gain screen?
A: A high gain screen is not always the best solution; brighter does not always mean better.
Higher gain projector screens often have reduced viewing angles/cones. While providing a brighter image for those within the cone; those outside often experience significantly diminished brightness. A smaller viewing angle means there is a smaller area that the audience must be seated in in order to experience the screen's maximum brightness.
Higher gain screens can also experience issues with "hotspotting". When viewing the screen from the Zero Degree Viewing Angle the center of the image will appear brighter than the outside edges. This is less noticeable with screen gains of 1.3 and below and becomes more noticeable on many surfaces as the screen gain increases.
Some higher gain surfaces also have difficulty with accurate color reproduction. Red, green and blue colors are often not reflected uniformly causing noticeable color shifting as one changes their viewing angle.
(*This is not the case with certain premium high gain screens such as the Vutec SilverStar SSX which boasts an incredible 6.0 gain without many of the issues discussed above.)
Lower gain screens have their advantages as well. Lower gain screens reflect all light back at a diminished ratio; not just the projector's light. Lower gain screens are good options to help reduce the amount of ambient light that gets reflected back to the audience when specific ambient light rejecting surfaces are not used.
Lower gain screens also help to bring out more vivid blacks and enhance a projector's native contrast ratio. Lower gain screen are often used in conjunction with a high lumen projector in home theater setups.
In a dedicated home theater environment the ambient light is usually well controlled so a specific ambient light rejecting surface is not necessary.
With lower lumen projectors, a 1.0 gain screen is often the recommended surface.
Your room's lighting conditions, audience's seating configuration and projector specifications all factor into determining which screen surface to select.
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