Gain vs energy - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-24-09, 05:59 AM Thread Starter
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Robert

Join Date: Feb 2009
Location: Sweden
Posts: 93
Re: Gain vs energy

Quote:
custard wrote: View Post
robert,
first of all well done with the calculations
Thank you. I'm happy to contribue if possible to this think tank.

Quote:
custard wrote: View Post
robert,
when we are talking about total light reflected we need to think in 3 dimensions rather than 2. we cannot simply use the area under the curve.
Granted. I get your point. To be blunt, we actually only measure in 1 dimension. My claims of reflected light energy is based on the assumption that the single 1 dimension (X-axis) measurement is representative for all Y-axis measurments.

From an engineering point of view the best comparative situation I know of, are the so called "antenna lobes" of an antenna. They are visuilised via two diagrams. One displaying the distribution as seen from above and one as seen from the side.

I await your thoughts of what you mean by 3 dimensions.

What sparced my idea is that the GAIN figure today is basically useless as a description of the properties of a screen.
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Old 02-24-09, 11:58 AM
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custy

Join Date: Jun 2008
Location: walsall, uk
Posts: 184
Re: Gain vs energy

my first thought is that we need to take into account all the angles beginning at on axis at 0 degrees to 90 degrees where no light is reflected.

now the hard part of putting the next thought into words.

as we move from 0 to 90 degrees we need to apply an extra value to multiply to the integral. this may result in an exponential realationship between gain and degrees to take into account that at larger angles more light is being projected.

at 10 degres the circle formed by the reflected light is smaller than the circle formed at say 50 degrees.

e.g.
if gain was 1.5 at 10 degrees
and gain was 1.5 at 50 degrees

then there is still more total light being reflected at 50 degrees as the circle of light is larger at this angle.

i will try and explain this abit better with some diagrams at some point.

the formula may need to apply 'tan' to the degrees values as a starting point. i 'll try and calculate a formula but i may need your help as my maths brain has not worked at this sort of thing since my school days.
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Old 02-24-09, 12:50 PM Thread Starter
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Robert

Join Date: Feb 2009
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Posts: 93
Re: Gain vs energy

Interesting. I use math in my work as Submarine Engineer so I might be able to help you in that area.

But I am beginning to understand what you are after, and I do believe that you are heading in the correct direction. But I believe that the path you are heading is pointing towards absolute figures. You are correct that if you regard a "cone of light" that is narrow, the "amplitude" i.e. the height of the cone can be very high, even though it actually does not hold as much volume as a more wider but lower cone.

But what I am trying to wrap my brain around is a way to present to the user a set of relative figures that all relates to the famous Magnesium Block. I totally agree that for an absolute quantification of the reflected light you would have to do a so called curve integral. But the normal viewrws do not sit in a circle *wink*. We sit in a row in fron of the screen. And measurements show that there are screens reflecting substantially more light energy "in the relevant line of sight of the observer".

So a parameter that I do believe is relevant to add is the fact that various screens may perform different depending of the relative monting hight of the PJ.

Last edited by robert_1967; 02-24-09 at 01:04 PM.
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Old 02-24-09, 12:54 PM
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custy

Join Date: Jun 2008
Location: walsall, uk
Posts: 184
Re: Gain vs energy

hopefully this diagram shows as the angle increase the total light at the mentioned angle increases aswell.
the perimeter of the circles would denote the amount of points where light has reflected to at one angle.
the larger the perimeter the more points are present.

the total reflected light/energy at a particular angle would be the sum of all those points.

so there are more points at 50 degrees than 10 degrees.

the area under the curve only takes into account 2 points for all angles.
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Old 02-24-09, 01:04 PM
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custy

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Re: Gain vs energy

Quote:
robert_1967 wrote: View Post
Interesting. I use math in my work as Submarine Engineer so I might be able to help you in that area.
wow, that is a job i would find really interesting!
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Old 02-24-09, 01:10 PM
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custy

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Re: Gain vs energy

Quote:
robert_1967 wrote: View Post
But I am beginning to understand what you are after, and I do believe that you are heading in the correct direction. But I believe that the path you are heading is pointing towards absolute figures. You are correct that if you regard a "cone of light" that is narrow, the "amplitude" i.e. the height of the cone can be very high, even though it actually does not hold as much volume as a more wider but lower cone.

But what I am trying to wrap my brain around is a way to present to the user a set of relative figures that all relates to the famous Magnesium Block. I totally agree that for an absolute quantification of the reflected light you would have to do a so called curve integral. But the normal viewrws do not sit in a circle *wink*. We sit in a row in fron of the screen. And measurements show that there are screens reflecting substantially more light energy "in the relevant line of sight of the observer".
yep, the total light figure is not relevant to the viewers at all.

my only reasoning for looking at these calculations was to show that a screen cannot reflect more than 100% of the light.
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Old 02-24-09, 04:37 PM
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Don

Join Date: Oct 2007
Location: Central PA
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Re: Gain vs energy

Quote:
robert_1967 wrote: View Post
So a parameter that I do believe is relevant to add is the fact that various screens may perform different depending of the relative monting hight of the PJ.
That is absolutely correct. All of the screens measured here, except the HP, reflect like a mirror so the brightest view would be a ceiling mounted PJ with the viewer at the same, but opposite, angle of projection. This is the way the data was gathered.

The HP is retro-reflective so the PJ should be at the same level as the viewer to produce the brightest screen.

Sadly, I will have to admit that higher mathematics to me is counting over 20, but I am enjoying watching you guys work on the problem of gain data interpretation; and it is a problem. We can compare our resulting gain curves with those of commercial screens, but even those companies don't really tell you anything other than "higher gain equals a brighter image". I think there is much more info to be gotten from this data. For instance, the SILVER and Silver Fire screens hot-spotted, but none of the other screens did.
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Old 02-25-09, 02:32 AM Thread Starter
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Robert

Join Date: Feb 2009
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Posts: 93
Re: Gain vs energy

Quote:
custard wrote: View Post
yep, the total light figure is not relevant to the viewers at all.

my only reasoning for looking at these calculations was to show that a screen cannot reflect more than 100% of the light.
I apologize for my poor English if I gave anyone the impression that I was promoting the idea of a screen that contradicts the laws of nature. Custard is of course very correct that a screen can never reflect more than the PJ's output. My figures above that indicate something more than 100% is a relative figure when the SUT (Screen Under Test) is compared to the Magnesium block.

My efforts lie in the attempt of augmenting the GAIN parameter to actually include some useful information.

Now to the topic of retroreflectiveness vs (whatever the other one was called).
Assuming that the SUT is homogenous in the X and Y axis. In other words, the screen behaves identically regardless if we rotate it 90 deg or even have it up-side-down. Assuming this, then we can emulate the placement of the PJ by using a PJ but we tilt it 90 deg. Placing the PJ, tilted, on one far side or even outside the width of the SUT will represent a cieling mount. Now using the same equipment you allready have you now can get a curve describing wheter it is a retroreflrctive or other type of screen. If it is retroreflective you should get the peak when you are measuring under the PJ. If it is (the other type) you should get a peak at the proper reflection angle. If you can do some curves I might come up with an idea how to convert it into a factor. Perhaps R-index. R-index may vary from -1 to 1. -1 is an ideal retroreflective screen. 1 is an ideal reflective screen (mirror). 0 would then be the ideal lambertian screen.

A few hypothetical results: (RI = Reflective index)

Black Widow, 0.88:0.87:0.87, RI 0.5
S-I-L-V-E-R, 1.37:1.18:1.01, RI 0.8
Winter Mist 0.94:0.94:0.94, RI 0.1
DL Highpower, 2.69:2.28:1.95, RI -0.7
DL Perlecent , 1.46:1.33:1.22, RI -0.4

Any thoughts on this before I move on to a way of quantifying Hotspotting?
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Old 02-25-09, 05:25 AM
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custy

Join Date: Jun 2008
Location: walsall, uk
Posts: 184
Re: Gain vs energy

Quote:
robert_1967 wrote: View Post
I apologize for my poor English if I gave anyone the impression that I was promoting the idea of a screen that contradicts the laws of nature. Custard is of course very correct that a screen can never reflect more than the PJ's output. My figures above that indicate something more than 100% is a relative figure when the SUT (Screen Under Test) is compared to the Magnesium block.
as i have spent over a day trying to calculate and quantify how much light is reflected by MgCo in relation to the dalite hp and other screen samples i would like to show some of my formula.

everyone/anyone - feel free to correct me/help me with this as i probably havn't calculated everything right.

to calculate all gain at one angle

gain=G
angle=A

perimeter of circle = 2 x pi x R

R = sin A x G

where R = radius of circle made by angle A at given gain G

therefore perimeter = 2 x pi x(sin A x G) = total gain at that angle A

to calculate total gain at all angles
total gain at all angles = the sum of 'total gain at angle A' from 0 to 90.

total gain at all angles = the area under curve (INTEGRAL) of x,y graph
where x= angle, y = total gain at angle A

trapeziod rule to calculate area under curve in excel gain spreadsheet.

results abit later
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Old 02-25-09, 06:42 AM Thread Starter
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Robert

Join Date: Feb 2009
Location: Sweden
Posts: 93
Re: Gain vs energy

You are correct as far as I can see . Very good presentation of your reasoning . I am not contradicting you in any way. I agree that taking all spacial coordinates into account we will get different results. We might even get the result that the pure Magnesium reflects most energy as it is Lambertian in its nature and has almost GAIN 1 at extreme angles, which in line with your own reasoning, would generate a large contribution to the total reflected light.

But other than from a academic point of view, why pursue this line of reasoning? We agree, didn't we , that our target is to come up with a better GAIN figure that gives the user more value and understanding of the relevant screen properties, i.e. in the line of sight of the viewer. Or have I missed something? In that case I blame my juvenile innocence

Last edited by robert_1967; 02-25-09 at 06:54 AM.
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