There seems to be constantly changing buzz words in the Screen world such as 'ambient rejection', viewing cone, texture- but one that always stays at the top of the list is gain.
Since we started this thread off about gain and some of the ways that is achieved, I thought it would be interesting to show what the experts have to say.
Quote:
| Da-Lite wrote:
Gain, we must always remember, does not imply amplification. No screen can add power to the display. All available brightness is created by the projector and only the projector. So when a gain screen exhibits increased brightness at its center, it is certain that it has robbed that extra energy from somewhere else. With all diffusion screens, therefore, the higher the gain, the lower the uniformity. This is the principal reason to recommend low gain screens whenever possible. |
I'll let that sink in for a minute.
Okay times up! This is from the makers of the High Power (HP) screen that has a gain of 2.8.
But why would they say this if they make a high gain screen? High gain does have its uses but is more of a specialty screen. The typical theater brightness is between 12 to 22 foot Lamberts of light at the screen. To put that in perspective, Televisions produce 35 fL of light and some are even higher.
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| | What is a foot Lambert or fL? That is the amount of light at the screen. To calculate this use the formula
Keep in mind that this is Video Optimized Lumens, not the maximum Lumen rating of the projector- those two numbers are very different. Also the above formula is assuming a screen gain of 1.0. To calculate for a different screen gain, multiply the result by the screen gain. | |
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Most Home Theater setups only require a screen with gain ranging from .85 to 1.8. The typical range is 1.0 to 1.6. Above 1.8 things start to get tricky and sticky. Most screens over 2.0 in gain switch over to Retro-Reflection screens.
Okay I know some are saying 'Hold on, you're throwing more terms around again'. A retro-reflection screen is specially made so the light hitting the screen is reflected back along the projection axis. An angular reflective screen the projected light reflects at an angle equal to the projected light's incident angle. Think of angular reflection like a pool table and you're making a bank shot into the side pocket, and retro-reflective is like a traffic sign- when your car's headlights shine on the sign the light is reflected back at your eye and the sign appears bright.
Here is what these two setups look like, this graphic is one I am sure everyone has seen many times: The example on the left is a retro-reflective screen and on the right is an angular reflective screen.
So a quick recap:
- Gain is the ratio of brightness of your projection screen material to a white standard such as barium sulfate or magnesium carbonate. The higher the gain, the lower the viewing cone becomes.
- Retro-Reflection screens are a high gain screen that reflects light back towards the source, like a stop sign.
- Angular Reflection screens reflect the projected light away from the light source, like a bank shot in pool.
So what do we need?
As stated, the typical screen gain used for Home Theaters is between 1.0 and 1.6. That isn't to say there aren't special situations that may require higher gain, but that is more the exception than the rule.
12fL of light at the screen is the minimum recommended amount of brightness for a fully light controlled room. When initially designing your Home Theater layout, use a 1.0 gain as your reference and starting point. Once you determine what the fL of brightness at the screen will be for your proposed setup you can start looking at gain. If the fL are below 12 then a screen with enough gain to bring it to that level of brightness is strongly recommended. If your setting has ambient light issues, then the screen will need to have even more fL of brightness at the screen as well as some other specifications that we'll get into later. What I have found is that 12fL is fine for controlled lighting, 13-14 is even better. Much more than that and the image starts to become too bright and can cause eye fatigue. If 12fL of light is the minimum for a light controlled room, I would say 14 fL is the minimum for ambient light, 15-16 is ideal.
Ambient light has always been a problem though with projectors. In this case gain isn't necessarily the answer. Gain is only a tool to get the required fL needed. If your projector is bright enough to produce 14-16fL of light at the screen then gain isn't as big of a factor. Gray screens are typically lower in gain and many are less than 1.0, so take that into consideration with your calculations. I would drop to .85 for the gain in the equation. Again, if you can hit 14-16fL you are fine. If not, then a brighter projector, smaller screen, or higher gain is needed.
Here is an example of 14 fL on a gray screen with an enormous amount of not just ambient lighting, but ambient sunlight.
These were from a 1700 maximum Lumen rated projector (video optimized is around 470 fL) on a properly balanced neutral gray screen with a matte finish. The reason I posted these was to demonstrate that ambient viewing is very attainable and easy too as long as certain guidelines are met.
I personally don't watch things on the screen during the day, but many people want to so I test for that environment too.
The best thing anyone can do when it comes to direct sunlight is to try and kill it at the source. Blackout Cloth is very popular for screens, but it also works extremely well for its intended use, which is to block incoming light during the day.
Some people though do not want their living room to look like a cave during the day. This obviously is a compromise they have accepted, but there are things that can be done to help.
Window film can knock down a lot of incoming light and I highly recommend it. Here are some examples of how much light various films allow through. VLT - Visible Light Transmittance, tells how much light can pass through the film. The lower the number, the darker the film.
So with the right setup where the projector and screen meet the 14-16 fL criteria and with a little effort to knock down the incoming ambient light, a projector is usable even during the day. Keep in mind it will never look as good and stunning as it does when the lights are out, but a very watchable image can easily be achieved.
We covered a lot of ground quickly with the first post and this one. I will get something up for viewing cone and a few other topics, but feel free to jump in at any time with any questions. This thread is not totally an informational thread like the stickies tend to be and is an open format thread.
For specific questions about a particular commercial screen or DIY application, please direct those to the appropriate person or thread. This one is more for those annoying general questions and confusing issues that a lot of people have.