Information About Screen Gain
The gain of a projection screen is a property that you will come across frequently when comparing screens. Understanding gain can be important in making sure that you get the most out of your presentation equipment. In this Bamboo AV article we will explain what screen gain is, the difference between a low gain and a high gain screen, and the applications where a low gain screen surface or a high gain screen surfaces is the best choice.
What is gain?
A projection screen’s gain is basically a measure of its reflectivity – i.e. how much light the screen reflects, and ultimately how well the screen redirects light from the projected image to the audience. Gain is measured by comparing the ratio of light a screen reflects to the light reflected from a standard board with a surface made from magnesium carbonate, which is a very white chemical coating. A screen with a gain of 1 means that the screen reflects exactly the same amount of light as that from the white board. A screen with a gain of 1.5 means that it reflects 50% more light than the white board, and a screen with an 0.75 rating means that the screen reflects will reflect 75% of the light from a white board – i.e. 25% less light. Gain is measured from the viewing angle where the screen reflects the most light, which is directly in front and at a 90 degree angle to the screen.
Low gain vs. high gain
When buying a projector screen, most people have to make the choice between a screen made from a high gain material and a screen made from a low gain material. At first glance a high gain screen may seem like the obvious choice, since higher reflectivity means the image on the screen will be brighter – which is usually assumed to be a good thing. However, a high gain screen also has its drawbacks. In fact, each value of screen gain has its own advantages and disadvantages.
Low gain’s viewing angle vs. High gain’s brightness
The greater the gain ratio, the greater the amount of light that will be reflected. However, the trade-off is that the viewing angle of the screen will decrease. Screens made with material designed for a low gain ratio disperse light evenly over wider angles, whereas high gain screens are constructed to reflect light back towards the centre of the screen. For example, a high contrast grey projector screen with a low gain of 0.8 boasts a 180° area of view (also called a “viewing cone”), but less light is reflected towards the audience. On the other hand, a high gain glass-beaded screen surface has a gain rating of 2.5, meaning that it will reflect much more than the grey screen, but the angle the screen can be viewed from decreases to a 60° viewing cone.
The pictures below show the viewing cone for a high gain screen on the left, and a low gain screen on the right.
A high gain screen’s viewing cone A low gain screen’s viewing cone
High gain and hotspotting
A further problem with high gain screens is their susceptibility to a problem known as hotspotting. Hotspotting means that there is a disparity across the brightness of the screen – i.e. certain areas of the screen may appear much brighter than others. Many people find this side-effect irritating since it can be distracting while watching a film for the centre of the screen to appear visibly brighter than the edges. Hotspotting is usually only an issue in screens with a gain ratio of 1.3 or above.
Where is low gain appropriate?
As we have seen, the screen with the highest possible gain ratio may not be the right choice for your application. While it does allow for high image intensity, for home theatre owners the wide viewing angles that low gain screens offer can be preferable. This is because it allows for seating to be placed all around the screen and gives everyone the same viewing experience. If a very high gain screen was used for a really bright image, only those sitting at the middle of the screen will see the brightest possible image and those in seats at the side would suffer.
Furthermore, depending on the viewing angle, the projected image will appear differently due to the fact that high gain screens characteristically do not reflect red, blue, and green colours equally.
For the true home theatre enthusiasts who can control the light in the room and who seek the best quality image, low gain screens are preferable in delivering the optimum experience.
Where is high gain appropriate?
The situation in which a high gain ratio can be advantageous is one where the audience is situated in a narrow seating plan directly in front of the screen. In this scenario the screen will appear visibly brighter, and can thus enhance the effect of a presentation, without worrying about the loss of wider viewing angles. This can be extremely beneficial if using a projector in an environment where the amount of light in the room cannot easily be controlled.
As a result, high gain screens are usually implemented in environments containing only a limited number of audience members such as in classrooms or business meetings. Alternatively, those using portable projectors who may not be aware of the environment they are going to be presenting in usually prefer a high gain screen as it can ensure that, no matter how bright the venue, the projected image can clearly be seen.
How to avoid screen gain
To completely avoid the side effects of lower gain or higher gain screens, the only solution is to choose a screen with a neutral gain ratio of 1.0. Matt white screen surfaces typically have 1.0 gain, and these screens reflect light evenly in every direction. An audience viewing a matt white surface will see an image that is consistently and equally uniform throughout, regardless of the angle of projection angle or the angle they are viewing the screen from.