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

Old 02-22-09, 03:58 AM Thread Starter
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Robert

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

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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Old 02-22-09, 10:44 AM
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custy

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Re: Gain vs energy

Quote:
robert_1967 wrote: View Post
Is it possible, in theory, to get a screen that reflects MORE energy in total compared to the ref?
theoretically a material could reflect all light 100% that is emitted onto it without any absorption.
but the total reflection cannot increase above 100%.

i think the reference comes very close to the ideal as does titanium dioxide that you have mentioned previously.

the total light reflected would be proportional to the area under the gain curves. which in turn is reduced if the material is darker in color (absorbs more light)
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Old 02-22-09, 04:04 PM
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Don

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Posts: 3,772
Re: Gain vs energy

Quote:
Quote:
:robert_1967 wrote:
3/ Is it possible, in theory, to get a screen that reflects MORE energy in total compared to the ref?
Mech replied: If one were to use a 30 degree energy value I'd guess the high power would. But that's without me looking at the numbers.

I definitely think this may warrant further discussion! Or I could very well be cuckoo... or both!
I have a bad head-cold that is playing hob with my thinking ability, so I'm not quite getting the gist of this thread yet; but to the above question I would say the answer is no for TOTAL reflected energy. Now if you limit the "viewing angle" then you can easily get gains over a Unity Reference. A Unity Reference is a material that perfectly diffuses the light hitting it so it is reflected back equally at all angles; this surface will have the same brightness when viewed from any angle. As the target increases in reflective qualities (either specular or retro-reflective) the TOTAL reflected light won't change much, if at all, but the viewing cone will shrink; the more reflective (mirror-like) the surface, the more narrow the viewing cone. This action continues until we reach the point where the target is actually a front-surface mirror that will reflect the light striking it at the same, but opposite, angle and has maximum "gain", but minimum viewing cone.

Silver Fire is a good example of a "screen mix gone wrong". The theories behind this mix are interesting, but simply don't work. More will be said on this at a later date, but for now, it is not neutral in color, it has too much gloss and the very reason behind it's supposed "extra" performance (RGBY color components) simply doesn't make sense when viewed from either an artistic or scientific view. A neutral gray is a neutral gray no matter what pigments it is mixed from. The author of this mix has recently stated that the "blue push" of the mix is actually a good thing in that it absorbs more ambient light than a neutral gray screen of the same shade would; that too is wrong.
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Old 02-23-09, 07:52 AM Thread Starter
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Robert

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

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
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
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
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

Last edited by robert_1967; 02-23-09 at 08:27 AM.
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Old 02-23-09, 09:31 AM
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Don

Join Date: Oct 2007
Location: Central PA
Posts: 3,772
Re: Gain vs energy

Very, very interesting stuff Robert!

Those of us who are "arithmetically challenged" like myself will have to ponder of this awhile.

Something that may have an impact on your figures is that these values are taken with a 1 degree spot-meter. I think this is the main reason the Unity Reference seems to be absorbing light. We simply aren't measuring all the light being reflected.

The measuring procedure is to not only line up the light meter "left and right", but to also align it "up and down" so that the meter is reading the highest reflective value the screen will produce.

The High Power screen is the only retro-reflective screen in this group and it behaves differently than specularly reflective screens. It would be interesting to try to quantify that difference.
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Old 02-23-09, 01:46 PM
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custy

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Re: Gain vs energy

robert,
first of all well done with the calculations

i've given this abit of thought and i think there is abit of a problem with just using the integral to find the area under the curve and then relating that to total light/energy reflected.

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.

the area under the curve, or the integral of the gain curve will provide values which are 2-dimensional,
while the total energy reflected should be a 3-dimensional value.

or to put it differently, we are only taking the 'x' and 'y' axis into account and not the 'z' axis.

i'll try and draw a diagram to show why i think that there is alot more light energy at larger angles than is shown on the gain curves.

i will also try and explain this abit further when my brain starts remembering what it was taught all those years ago.
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Old 02-24-09, 05:59 AM Thread Starter
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Robert

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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

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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

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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

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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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