Gain vs energy

[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?

[mechman]

Robert,

Just a quick note. I'm gonna have to digest what you're saying here and get back to you after church. I may need a bit of clarification as well. Expect more later.

mech

[custard]

robert_1967 wrote:

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)

[mechman]

robert_1967 wrote:

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).

Correct

robert_1967 wrote:

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.

Correct. Look at Black Widow.

robert_1967 wrote:

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.

Silver Fire is a bad screen in my view. As for light being 'blocked' I'd say no. It's just not being reflected that way. It's an excellent example of "polyurethane gone wild" in my eyes! The polyurethane is more than likely ruining what little reflection it would pick up from the mica. And concentrating what little it can add to the on axis gain. Is that making sense?

robert_1967 wrote:

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.

Oh I think I see what your trying to quantify now, the total light from all angles with reference to MgCO. I don't think that would be a good quantifier for a screen because it would be a total energy number and I'd guess 90% of theater users wouldn't care about that last 30% of light lost. But I think I see your point and I think it is something we could do. Maybe do something for 0-60degrees and wash out the last 30 degrees? We'd have to figure out which angled measurements to include. So if I'm following what you're saying, take the gain from each angle and divide by the number of measurements for a total energy equivalency. Is that right? Bud over at the other forum was a big energy guy. I never really thought it was necessary as the current standards explained things quite well in my mind. But I'm open to it! I would guess the highest number would be the standard (magnesium carbonate) and anything that lines up close to it would be good. And maybe we could have a 30 degree enrgy chart and a 60 degree energy chart - mainly because I think the High Power may be better served this way.

robert_1967 wrote:

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?

Nothing is ever blocked. It's either absorbed or reflected.

robert_1967 wrote:

2/ Why is the totally reflected amount of energy not used as a "performance index" for a screen? RI=Reflection Index

Don't know. Are we gonna start something:? I nominate you! You have the data. Now let's hash out a HTS standard.

robert_1967 wrote:

3/ Is it possible, in theory, to get a screen that reflects MORE energy in total compared to the ref?

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!

[Harpmaker]

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.

[mechman]

Robert,

You may have to expand on your energy formula for both Harp and I. I was just playing around with the numbers and there's a couple of ways to do things. Let us know how you would calculate the energy based upon gain.

I'm still not sold on this because I think gain relates this.

[robert_1967]

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

[Harpmaker]

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.

[mechman]

Robert,

I'm with harp on the pondering for awhile. I don't have enough time at the moment to digest this. Right now I'm a bit busy trying to keep you up late again tonight. Check the web page out again later. I'm adding all of the readings from the pj bulb at 100 and 70 IRE. Maybe you can take a nap right now?

I'd like to add that it does seem very intriguing!

[custard]

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.

[robert_1967]

custard wrote:

robert,
first of all well done with the calculations

Thank you. I'm happy to contribue if possible to this think tank.

custard wrote:

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.

[custard]

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.

[robert_1967]

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.

[custard]

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.

[custard]

robert_1967 wrote:

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!

[custard]

robert_1967 wrote:

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.

[Harpmaker]

robert_1967 wrote:

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.

[robert_1967]

custard wrote:

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?

[custard]

robert_1967 wrote:

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

[robert_1967]

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

[custard]

sorry robert

i'll chuck the readings

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.

[robert_1967]

custard wrote:

sorry robert

i'll chuck the readings

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 . I bow for your wisdom Its only from discussion and challanged thought we progress. I am ashamed if I have put you off in any way .

[mechman]

Wow! This has developed into something way above my pay grade!

[robert_1967]

mechman wrote:

Wow! This has developed into something way above my pay grade!

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.

[Harpmaker]

robert_1967 wrote:

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.

First, I am simply in awe of what Robert and Custy are doing here.

I don't mean to "straddle the fence", but sometimes you have to see the big picture before you can examine a portion of it clearly. I think we may really be on to something here that will be a major aid to the entire projection screen industry! This is big stuff!

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.

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.

Please keep it up, you guys are doing great!