[Harpmaker]

: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.

 

[Harpmaker]

Very, very interesting stuff Robert! :T

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.

 

[Harpmaker]

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. :T 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.

 

[Harpmaker]

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. :hail:

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! :T:T

 

[Harpmaker]

With the risk of beeing expelled from this forum ...

Not likely! :bigsmile:

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.

From a pure physics point of view this is correct, but when we stay within the parameters of real screen values (a mirror makes a horrible screen :bigsmile and keep the industry-standard magnesium carbonate reference target (which is a very bright white as well as a perfect diffuser); the answer is no, we can't have a screen show more total reflection than the reference; but we can have a screen that shows more on-axis reflection.