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Discussion Starter · #1 ·
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.

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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Discussion Starter · #7 · (Edited)
Very interesting thoughts guys.

Custard, well I am just questioning if the Magnesium Ref sample reflects the same amount light energy as a perfect mirror. And looking at my calculation result below, the DL High Power proves my point.

Ok. Hard data.
Look at DL High Power. Even to the naked eye one can easily see that the integral from -75 to +75 degrees far exceeds 150 units (in lack for a better word). Why 150? Well if you draw a line at gain 1 from -75 to +75, the area is 150. I took data from your spread sheet and put it into my rudimentary model. (Linear approximation between samples).

This is my results on total reflected light based on -75 to +75 degrees measurements:
Ref sample: 150
DL Highpower: 233
Black Widow: 130
Silver Fire: 97
S-I-L-V-E-R: 125
Winter Mist: 139
Veil : 113
Parkland Polywall: 141
DL Mat: 149
DL Cinevision : 127
DL Perlecent : 154
Carada brilliant white : 164
Elite Cine White : 151
Wilsonart Designer White : 158

So we actually have 5 screens reflecting more light than the ref sample with DL High Power being outstanding.

Now. Lets add the quality of viewing cone. Is -75 to +75 degrees a relevant angle? I’d suppose not. Therefore I have done the calculations on +/- 30 deg and +/- 45 deg. I have also related it to the ref sample in accordance with normal GAIN procedures (to get away from the 150 figure).

Result is as follows. Screen name followed with the amount of reflected light in relation to the ref sample in +/- 30 deg and +/- 45 deg.

Ref sample, 1,1
Black Widow, 0.87, 0.87
Silver Fire, 0.95, 0.80
S-I-L-V-E-R, 1.18, 1.01
Winter Mist 0.94, 0.94
Veil, 0.77, 0.77
Parkland Polywall, 0.97, 0.96
DL Highpower, 2.28, 1.95
DL Mat, 1.01, 1.01
DL Cinevision, 1.08, 1.00
DL Perlecent , 1.33, 1.22
Carada brilliant white, 1.21, 1.16
Elite Cine White, 1.04, 1.04
Wilsonart Designer White, 1.21, 1.16

So. Maybe a better way of describing GAIN may be to include the 30 and 45 deg accumulated reflected light. In other words the GAIN of Black Widow should be 0.88:0.87:0.87, meaning that straight on zero degrees we have 88% reflection. On 30 degrees we have an ACCUMULATED reflection from zero-30 of 87%. On 45 degrees we have an ACCUMULATED reflection from zero-45 of 87%.

The new list gets to be:
Black Widow, 0.88:0.87:0.87
Silver Fire, 1.04:0.95:0.80
S-I-L-V-E-R, 1.37:1.18:1.01
Winter Mist 0.94:0.94:0.94
Veil, 0.77:0.77:0.77
Parkland Polywall 0.98:0.97:0.96
DL Highpower, 2.69:2.28:1.95
DL Mat, 1.01:1.01:1.01
DL Cinevision, 1:15:1.08:1
DL Perlecent , 1.46:1.33:1.22
Carada brilliant white, 1.26:1.21:1.16
Elite Cine White, 1.04:1.04:1.04
Wilsonart Designer White, 1.26:1.21:1.16

This way of representing GAIN gives relevant data to the consumer. It answers the question, how much light does it reflect in relevant angles? And indirect, we also get a feeling for the view cone.

So in my humble opinion, from a strict reflection point of view, I nominate Wilsonart Designers White and Carada brilliant White with idendetical (1.26:1.21:1.16) in GAIN, to be my best screen chiose if you are in a need to "increase" your ammount of reflected light of any reason.

Does this make any sence :coocoo:

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Discussion Starter · #11 ·
first of all well done with the calculations :clap:
Thank you. I'm happy to contribue if possible to this think tank.

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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93 Posts
Discussion Starter · #13 · (Edited)
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.

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Discussion Starter · #18 ·
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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Discussion Starter · #20 · (Edited)
You are correct as far as I can see :yes:. Very good presentation of your reasoning :T. 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 :scratch: , 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 :innocent:

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Discussion Starter · #22 ·
sorry robert :hide:

i'll chuck the readings :innocent:

to give you an idea mgco3 is coming up tops with the carada for 90 to -90 degrees with an an assumption that the value at 90 degrees is equal to 75 degrees. HP is showing less from what i remember.

i'll stop now. i wont pursue this anymore.
No no, you have successfully made it very clear that from a physical and strict scientific point of view, reflected light energy is something other than what the viewer perceives. It was I, who in my eager to simplify the reality put up several boundaries and made false claims about reflected energy that you so correctly reacted on. All credit to you Custard :T. I bow for your wisdom :yes: Its only from discussion and challanged thought we progress. I am ashamed if I have put you off in any way :sweat:.

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Discussion Starter · #24 · (Edited)
Wow! This has developed into something way above my pay grade! :nerd: :dizzy:
LOL :).

But really, mech and of course all other out there, what do you think about the HTS suggestion?

GAIN X:Y:Z => X=Peak Gain at 0 degrees, Y=percieved acumulated reflected light from 0-30 degr, Z=percieved acumulated reflected light from 0-45 degr. (all figures related to the magnesium block)

RI => Reflective Index. Range from -1 to +1. -1 equals 100% retroreflective and +1 is a mirror. Zero is a ideal lambertian screen.

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Discussion Starter · #28 ·
Happy that you enjoy our artithmetics :bigsmile:

Basically, what you could do is 10 deg incremental measurements 0-60 deg if that is enough in your opinion.

The easy way out is to do this for every 10 deg interval:
Gain 0 minus gain 10. This gives us the delta.
Divide delta with 2.
Add the half delta to Gain 10. This gives us the average Gain between 0 and 10.
Multiply this average with 10, as the interval between measurments is 10.

Repeat this between all measurements and incrementally add the results.
Then you get the area under the gain curve which could represent an acumulated persieved light reflection of the screen from 0-60 deg.

Custard, I thought excel had some tools for integrals but I cant find any. Can you suggest better, more accurate ways of estimate the integral of the curve based om measurements from mech?

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Discussion Starter · #29 ·
As it now stands, a screen's gain figure is almost meaningless since all it tells you is maximum gain and gives no hint of other screen attributes; and even a gain-curve won't tell you if a screen is retro-reflective or specular reflective.
Very true. But we do have presented an idea about the retro/specular stuff above.

Perhaps something that should be taken into account in these proceedings is the "half gain angle", the angle at which the maximum gain figure is reduced to half it's value. If I remember correctly, this is the angle that commercial screen manufacturers use to come up with their viewing cone figure. I don't know if that angle should be taken into account in these formulae or simply given as a separate calculation.
I agree, but imo that is a very poor and blunt instrument to caracterize a screen. As you all have seen firsta hand the shape of the curve between zero and the point of 50% can vary dramatically. If you look at the loudspeaker industry the frequency range of a speaker is defined as between the two frequencys were it falls 3dB. But the 3dB rule does not say one word about how "flat" it is between. Lets not fall into the same trap.

Cust, any ideas on this? I do think it would be nice to have the 50% in there somehow...but how...:scratch:

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Discussion Starter · #34 ·
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 :p

Lets keep the focus on our discussions on user-value-issues.
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