# Gain vs energy

7386 Views 37 Replies 5 Participants Last post by  robert_1967
Mech. Your GAIN tests made me sleepless....ok, that would be stretching it, but it made me think.

As I understand it a GAIN curve is the relative value of amount of reflected light from various angles in relation to a known ref sample of Magnesium Carbonate. So if I measure the ref sample two times and calculate the resulting GAIN I would get a 1.0 from 0-180 degrees, right? (I know, futile example but I am trying to make a point here, bare with me).

Now, lets try to do a new GAIN measurement, but with a perfect gray, say of N9. In my world that would then result in a somewhat lower value, perhaps 0,95 (just an arbitrary figure), but it would be completely flat across 0-180 degrees. From a reflected ENERGY point of view, then we could say that the total amount of reflected energy is lower compared to the ref sample. From a math point of view, the area under the curve (the integral from -90 to +90) is less that the ref sample.

Now lets try to look at your measurements.

Silver Fire. It peaks at zero degrees just a hair above 1.0 and falls drastically 0.5 at 30 deg. From an reflection point of view I would like to see that as a very bad screen. The relative amount of reflected light at its peak is virtually the same as the ref. And tons of light is "blocked" as soon you look from the side.

S-I-L-V-E-R. Now we are getting more total light(energy) back compared to Silver Fire, but still clearly less than the ref.

Thoughts:
1/ The Silver Fire might have superior ambient light properties. The GAIN chart works both ways. Light not coming straight in will be blocked. Right?
2/ Why is the totally reflected amount of energy not used as a "performance index" for a screen? RI=Reflection Index
3/ Is it possible, in theory, to get a screen that reflects MORE energy in total compared to the ref?
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Lots to digest that's for sure!

I can definitely answer your one question, #3
"Is it possible, in theory, to get a screen that reflects MORE energy in total compared to the ref?"

Sadly the answer is no because we cannot create light. We can only have at most exactly what the projector is putting out and even that starts to diminish as soon as it leaves the lens. We can however make the image brighter on axis but at the expense of the off axis brightness. That's gain and as much as some want to claim 1.8 gain screens with 180 degree viewin cones, it is simply impossible with a passive device such as a screen.

Gain has always been a tricky topic. That's why I started a thread about gain and other confusing topics. One that also seems to fit this discussion (from what I have read skimming through so far) is specular gain. Don't forget about that aspect of things either.

A real mind blower of a question though is "can a screen with an overall gain of less than one still be said to have 'gain'?"

The answer is yes, but then what about the laws of light and physics and our ever present viewing cone? Look at Black Widow as an example. Normally a plain flat/matte gray in the N7.5 range would not be expected to have an overall gain any higher than .75 at best. Because of the properties of this particular screen (BW) it has a gain of .9, yet the shade is an N7.5. That would indicate we have gain, and yes we do, but the viewing cone is still essentially a 180 degree area.

Under a gain of 1.0 we still have less than our reference material. The difference is the added reflective materials throughout the screen. Since we're not dealing with a specular type gain achieved primarily through sheen, we maintain our diffusive surface.

Once we go over a gain of 1.0 there is no other way to increase the on axis brightness than to 'take' light energy that is normally reflected off axis and refocus that back to the center viewing area. Since we're taking more energy and refocusing it, and now on axis we have greater than our reference material, the viewing cone is more apparent.

This is a very interesting topic, but don't forget gain is just a tool used to achieve the required brightness for a given setting and screen size. Far too many people talk about gain as if it is a knob to adjust the image and make it 'pop' as some like to say. Gain quickly can get out of hand and then we not only have hot spotting, but after a point we can also experience color shifting off axis.

I don't know if I strayed from the topic, if so my apologies! I'll read each post thoroughly after I finish some evening work I have to do. Good topic though from what I read so far!
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I have guests over soon so I have not time to absorb all above. Will return.

Still a comment to Bill. I questioned ""Is it possible, in theory, to get a screen that reflects MORE energy in total compared to the ref?"

With the risk of beeing expelled from this forum I claim that the answer can be yes. Just to make my point, consider the idea of having a N6 gray as ref. Now if you measure the GAIN with the N6 as ref and test a white matt paint you will get the result that you indeed get more light back from the white compared to the N6.

I am not disputing the fact that we can only reflect the ammount of light actually reaching the screen and that is allway less than the PJ output. But if you think about it, a perfect mirror should reflect more light than a Magnesium block imo. There is a fraction of light that converts to heat in the magnesium.

But hey, look at me, now who is beeing academic here. I am sorry custy

Lets keep the focus on our discussions on user-value-issues.
One thing... never worry about being expelled for participating in a discussion.

I apologize about taking the thread off topic.
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